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Sound Thoughts on Door and Frame Assemblies: Exploring differences between STC and STL ratings

All images courtesy MegaMet Industries

All images courtesy MegaMet Industries

by Edward Wall Jr. and Allan C. Ashachik

When sound control acoustic door assemblies are selected, the usual way is to specify a sound transmission coefficient (STC) rating in accordance with established standards. Derived from testing at a series of frequencies within the range of human hearing, STC is a single number assigned to a door assembly that rates its effectiveness at blocking sound transmission. This sounds simple and logical, just like hourly ratings on fire doors, but the situation is far more complicated.

The challenge with having a catch-all solution in the form of specifying the ‘right’ STC comes down to the range of sound. For example, if a project concerns a high school band’s practice room, the noise that needs to be reduced comes from instruments ranging from the low-frequency (pitch) of a bass drum to the high pitch of woodwinds or chimes. For this application, STC would be appropriate since sounds from many frequencies all need to be blocked or reduced.

However, selecting the right door for a mechanical equipment room at the same school is quite different. Low pitch and constant machinery noise needs to be filtered out. Using the STC rating system for this opening could be much more expensive than necessary to be effective. Fortunately, there is another metric more suited to these situations—sound transmission loss (STL).

The STC rating is actually derived from an average of STL performances. Since STC relies on testing data that establishes the reductions at each individual frequency, the data can be used to determine the STL needed at a specific frequency or frequency range without additional testing.

Setting the stage
This article is not intended as a lengthy discussion of all aspects of sound control, designs, gaskets, or installation. Rather, it seeks to clarify some misconceptions about STC and suggest using alternate values and standards when specifying acoustic door and window assemblies for a particular sound control purpose or requirement.CS_October2014.indd

The authors believe STL is the definitive method of specifying acoustic assemblies, and better accomplishes what the sound-deadening qualities are to be required for a specific opening. On a practical level, this means the building owner gets what he or she really needs, often for less money. To make this argument clear, six myths must be examined.

Myth 1: “An STC rating in accordance with ASTM E90 is all that needs to be specified.”
It is important the reader be a least somewhat familiar with some of the ASTM standards applicable to lab testing and rating of sound control assemblies.

To that end, ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, describes the test chamber, testing method, frequencies to be reported, and other lab requirements. However, it does not contain the method of establishing the rating. A second standard like ASTM E413, Classification for Rating Sound Insulation, or ASTM E1332, Standard Classification for Rating Outdoor-Indoor Sound Attenuation, needs to be included.

ASTM E413 is used to define the 16 frequencies at which sound transmission losses in decibels are measured. It also establishes the sound insulation contour values of those frequencies and the sound transmission loss values for each corresponding frequency. From this, a reference contour can be created to which actual test data can be graphed and compared. Interestingly, the profile of this reference contour remains constant for all graphs and is shifted up or down on the graph to obtain a single STC rating (Figure 1).

ASTM E1332 is used to calculate an outdoor/indoor transmission class (OITC) and covers a range from 80 to 4000 Hz. This standard has an extended lower range of frequencies for which the results are calculated rather than graphed. The additional frequencies are intended to measure STL in decibels for outdoor to indoor sound exposure resulting in a different OITC rating. The calculations generally result in a somewhat lower single rating than does ASTM E413 for STC.

In order to convey the purpose of this article, two fictitious ASTM E90 test results—derived from two different examples—are shown in Figure 2. The columns listed show the 16 STL numbers achieved at each frequency of the ASTM E413 test. Ratings are at random and do not necessarily represent a specific door assembly or manufacturer—however, these sample numbers are not unusual.

Sample 1 would be typical of a less-expensive door assembly with an STC of about 40 while Sample 2 would represent an assembly costing two to four times as much with an STC of over 48. As the image illustrates, depending on the frequency of sound, one can save the client a lot of money by specifying the less-expensive door.












Myth 2: “A higher STC rating is always better, regardless of cost. Therefore, one should always specify an STC rating higher than what the client needs—just to be safe.”
To understand how those STL values relate to real-world conditions, the reference charts of common volume sources and approximate frequencies are provided as examples in Figure 3. Simplistically, to reduce the volume from a busy office with mostly male employees to that of a private office, the assembly should be capable of at least an STL of 40 at a middle frequency range. The lower cost Sample 1 would be sufficient in lieu of the more costly Sample 2 usually specified.

To reduce the noise from a bass drum or low-frequency vibrations, the maximum STL should be concentrated in the corresponding frequency range. Here, Sample 2 would be the better choice. Other noise sources should be evaluated accordingly and the correct door assembly chosen to meet the best STL at a certain frequency range. At higher-frequency ranges, Samples 1 and 2 are not really much different in performance, but substantially different in cost.

Neither ASTM E413 nor ASTM E1332 establishes an STC (OITC) value of the ‘perfect’ acoustic door assembly. To evaluate test results to a single number, they must be compared to this contour. The key to this comparison is referred to as the ‘deficiency’—any measured sound transmission loss (STL) variation below the contour. The STL measurements above are not considered variations. Unless otherwise noted, ASTM E413 limits these deficiencies to a maximum total of 32, and a maximum of eight at any single frequency.

For projects like this IMAX movie theater in Brimingham, Alabama (or the Nashville Sympohny on page 96) choosing a door with the proper acoustical ratings is critical.For projects like this IMAX movie theater in Brimingham, Alabama (or the Nashville Sympohny on page 96) choosing a door with the proper acoustical ratings is critical.

For projects like this IMAX movie theater in Brimingham, Alabama choosing a door with the proper acoustical ratings is critical.

Acoustical doors are available in a wide range of sizes for a wide range of applications, such as this Georgian power plant.

Acoustical doors are available in a wide range of sizes for a wide range of applications, such as this Georgian power plant.

Myth 3: “STC is a single number completely reliable to describe performance.”
Unlike fire door assemblies rated based on a certain time and temperature curve, the method of calculating STC by test data and deficiencies from a sliding reference contour can result in different ratings. The test lab will generally use the most advantageous graph in the test report. This will be the one with the highest STC or OITC rating that falls within the parameters of the deficiencies. This rating, however, may not be the one with the lowest total of deficiencies or the one closest to the reference contour. With that in mind, one can see STC expressed as a ‘single’ number does not necessarily mean it is the ‘only’ number available.

The five graphs in Figure 4 show how the STL remains constant while the reference contour is shifted up or down to determine STC. It is important to remember the STC is the point at which the reference contour (not the STL contour) intersects at 500 Hz. This means even though the STL at frequencies is identical in the five graphs, the sample could have multiple STC ratings depending on the variation parameters. For example, the maximum STC (complying with ASTM E413) of the assembly is 43 (with 30 deficiencies) in the graph in Figure 4a. If an STC of 44 is attempted—as shown in Figure 4b—the result is a failure at 42 deficiencies and nine deficiencies at 160 Hz.

The highest STC values with the lowest total deficiencies are:

  • STC 42, with 21 deficiencies as in Figure 4c;
  • STC 41, with 14 deficiencies as in Figure 4d; or
  • STC 40, with eight deficiencies as in Figure 4e.

STC ratings below 40 result in a lower number of deficiencies when the sound transmission coefficient is the only determining factor. This should demonstrate the rating method has far less reliability than what is associated with fire door ratings where the time and temperature curve is more consistent.

STCDoors_Figure 4a-4e

A: In this two contour chart, the cyan is STC 43 with 30 deficiencies, while the dark blue represents STL 41—both are at 500 Hz, as are all of the other Figure 4 graphs. B: Cyan is STC 44 with 42 deficiencies, and dark blue is STL 41. C: Cyan reprents STC 42 with 21 deficiencies, and dark blue remains as STL 41. D: The cyan line plots STC 41 with 14 deficiencies; dark blue is STL 41. E: Cyan is STC 40 with eight deficiencies; dark blue is STL 41.

























Myth 4: “It is fine to continue putting STC-rated door assemblies in Section 08 10 00.”
Under MasterFormat, Sections 08 11 13–Hollow Metal Doors and Frames, 08 12 13–Hollow Metal Frames, and 08 13 13–Hollow Metal Doors, are intended to describe common applications of swinging hollow metal (e.g. steel) doors and frames. Not all manufacturers capable of fabricating hollow metal doors and frames are also capable of fabricating acoustic door assemblies, especially those over STC 35. They may also not have the up-to-date testing data and technology to fabricate such specialized products. This could lead to a litany of exclusions or qualifications at bid time; difficult to manage and compare for any distributor or general contractor.

The correct section to specify acoustic door assemblies is 08 34 73–Sound Control Door Assemblies, as this incorporates the latest in acoustic door assembly standards (e.g. American National Standards Institute/ National Association of Architectural Metal Manufacturers Hollow Metal Manufacturers Association [ANSI/NAAMM HMMA] 865, Metal Doors and Frames) that describe qualifications, details, and requirements for this specialized product. This ensures the project benefits from the expertise of manufacturers who are familiar with sound control and have conducted a sufficient number of tests in various configurations.

Myth 5: “STC-rated assemblies can do everything other doors can do.”
In order to perform the specialized performance functions required of STC-rated assemblies, the internal construction of doors must be of sufficient mass or innovative design. In some cases, this may conflict with other performance requirements such as fire ratings, universal accessibility, security, life safety, or wind loads.

Documents such as the aforementioned HMMA 865—or HMMA 850, Fire-rated Hollow Metal Doors and Frames, and Steel Door Institute (SDI) 128, Guidelines for Acoustical Performance of Standard Steel Doors and Frames—contain design or other information useful in determining which performance functions are the most important to the project. For example, an STC-rated door assembly also required to have a 1 ½-hour fire rating might be located in an area where a 20-minute fire rating suffices. An STC-rated door assembly where the entire project is also specified as meeting accessibility needs may be in a critical sound-control room where the accessibility is not the main function.

Qualified manufacturers of these specialized products should be well-equipped to discuss and resolve such conflicts so the specifier can decide which is the most critical to the individual opening.

The windows and door for this West Point recording studio needed to meet certain sound requirements.

The windows and door for this West Point recording studio needed to meet certain sound requirements.

West Point University Recording Studio STC Windows











Myth 6: “The STC of the installed opening will have the same STC as the lab test.”
Documents like HMMA 865 and SDI 128 quite clearly dispute this myth. When tested in a lab according to ASTM E90, the instrumentation, room size, calibrations, ambient conditioning, humidity, or other factors—in addition to the installation of the test samples—must be controlled within established parameters. Pre-test inspections and adjustments are common. Such stringent controls are not feasible at the project site.

Although there are accepted standards for ‘field testing’ of STC, the results of such tests could be five to 10 points less than the lab-tested STC.

To be clear, this article does not intend to propose totally replacing the historic STC rating method. It does, however, introduce the option of specifying acoustic assemblies by using a sound transmission loss method at a certain frequency or range of frequencies for special situations. It is important to remember—unlike the STC rating method, the STL lab-tested data does not change.

Edward Wall Jr. is the president of MegaMet Industries, located in Birmingham, Alabama. He was nominated to the technical committee and then the executive committee of (NAAMM’s) Hollow Metal (HMMA) division. Wall is now closing in on two decades of manufacturing hollow metal and developing specialty door products. He can be reached at

Allan C. Ashachik is an independent consultant, providing services to steel door and frame manufacturers. Since entering the industry as a pencil and T-square detailer in 1968, he has been involved in all aspects relating to steel doors and frames from detailing to final quality assurance in acoustic, windstorm, detention, and fire-protective applications. Ashachik is the 2006 recipient of the A. P. Wherry Award, issued by the Steel Door Institute (SDI) to recognize individuals who have made outstanding contributions to the progress of standard steel doors. He can be reached via e-mail at

Car Dealerships and LEDs: Implement Sustainability and Reduce Costs

All photos courtesy Optec LED Lighting

All photos courtesy Optec LED Lighting

by Jeff Gatzow

When car dealerships try to outshine each other through the use of bright light on their lots, much of the illumination is wasted off the lots’ parameters. While these lights serve a dual purpose of attracting potential customers and as a 24/7 security system, they also devour energy.

There are more than 17,000 automotive dealerships in North America. On average, they use up to 18 percent more energy than a typical commercial building annually. Consuming $1.9 billion dollars in energy costs a year, lighting can represent up to 45 percent of those costs as dealerships emphasize marketing their inventory and differentiating their facility from the competition. This amount can add up to thousands of dollars in annual energy costs for a typical dealership.1

Optimized illumination performance enhances the appearance of vehicles.

Optimized illumination performance enhances the appearance of vehicles.










Saving opportunities
Reducing energy costs is a major consideration for dealerships, which is their third-highest overhead expenditure.2 In 2006, the National Automobile Dealers Association (NADA) formally endorsed the Environmental Protection Agency’s (EPA) EnergyStar Challenge by asking its 20,000 members to reduce annual energy use by 10 percent or more. EPA estimates if auto dealers cut their consumption by this amount, nearly $193 million would be saved and more than one million tons of greenhouse gas (GHG) emissions would be prevented.3

In 2007, NADA and Energy Star launched a joint Energy Stewardship Initiative to help auto dealers improve the energy efficiency of their facilities and operations. The initiative provides data, tools, and other strategies for dealers to implement improved energy practices and technologies at their facilities. Since this launched, more than 800 dealerships have improved the efficiency of their facilities by reducing energy use by 10 percent or more annually.4

Automakers have been climbing aboard the ‘green’ bandwagon for years, with low-emission, high-mileage vehicles that appeal not only to customers looking to save fuel, but also to buyers eager to participate in what is perceived to be an environmental solution. Now, dealerships are following suit. However, dealerships with large parking lots, numerous buildings, and 24-hour demand for light have energy challenges.

LED technology
One potential technology for car dealerships is the light-emitting diode. Light-emitting diodes (LEDs) differ from traditional light sources in the way they produce illumination. In an incandescent lamp, a tungsten filament is heated by electric current until it glows or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.

An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called a positive-negative (p-n) junction. When connected to a power source, current flows from the p-side (i.e. anode) to the n-side (i.e. cathode), but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).

All light sources convert electric power into radiant energy (i.e. visible and invisible light) and heat in various proportions. Incandescent lamps emit primarily infrared (IR), with a small amount of visible light and heat. Fluorescent and metal halide sources convert a higher proportion of the energy into visible light, but also emit IR, UV, and heat.

As a relatively new technology, LED luminaires currently cost more to purchase than traditional fixtures lamped with high-pressure sodium or metal halide light sources. However, the reduction in relamping expense and increase in energy savings typically lower overall lifecycle cost by about 50 percent.

According to information from the report “Unlocking Energy Efficiency in the U.S. Economy,” a comprehensive lighting retrofit eliminates overall energy costs by up to 75 percent, with the upfront costs recaptured in less than three years.5

Exterior LED luminaire technology has turned the corner from specialty applications to general illumination. Powering this important change is a combination of performance improvements in the core technologies, introduction of a wide range of well-designed products, and continued cost improvements.

The design of LED luminaires is a new world compared to traditional light fixture design. Optical, thermal, and power supply characteristics have a drastic effect on the longevity, performance, and affordability of light fixtures using LEDs.

The generation of luminaires using LEDs dictates the need to harness and manage as much of the light energy as possible. Misdirected illumination usually means wasted light, requiring the need to engineer even more initial light to reach target deliverable light levels. Of course, generating a greater amount of light means higher costs and more heat generation, and if poorly managed, can reduce fixture life.

To minimize the number of LEDs used its important to employ high-performance engineered optics, which allow for more efficiently captured and managed light. The result is superior light distribution with less waste. LED luminaires using high-quality optics are far better at improving light uniformity than any other technology available today.

The prognosis is positive. LED luminaires’ efficacy continues its overall upward progression, doubling in the past two years among tested solid state lighting fixtures. Further, color quality is also steadily improving, making exterior LED luminaires a viable alternative to traditional sources.

The bottom line for LED lighting systems is they have the potential to save a substantial amount of energy costs for lighting over the lifetime of a project. In addition to the energy savings, the long life of LEDs in well-designed systems will result in significant reductions in both labor and material costs for maintenance.

These photos show Gary Force Toyota’s lot illuminated with traditional metal halide fi xtures. A total of 63 of the 1000- W fi xtures were replaced with 240-W light-emitting diode (LED) luminaries for dramatic energy savings.

These photos show Gary Force Toyota’s lot illuminated with traditional metal halide fixtures. A total of 63 of the 1000- W fixtures were replaced with 240-W light-emitting diode (LED) luminaries for dramatic energy savings.











National dealership sustainability initiatives
In 2010, Ford introduced its Go Green Dealer Sustainability Program at three of its dealerships; the auto-maker is now planning to make changes at all 3500 dealerships nationwide. The initial three facilities—one in Florida, one in New York, and one in Nevada—implemented a comprehensive assessment and evaluation of their impacts, primarily from an energy consumption standpoint. Lighting was a key element of the retrofits, aimed at addressing both the quantity and the quality of the onsite lights.6

Ford continues to expand Go Green, as participants can now receive an energy assessment through the Ford Electric Vehicle (EV) Program. The goal of the Go Green program is simple: collaborate with dealers to implement cost-effective ways to improve the energy efficiency of their facilities. Going forward, it will continue to be a key component of Ford’s Dealer Electric Vehicle Program as the company expands its model offerings. As part of the certification process to sell EVs, Ford EV dealers undergo an energy assessment to identify opportunities to reduce their overall carbon footprint and lower their energy expenses.7

Additionally, in 2013 the Go Green energy assessment became an integral component of the U.S. Ford facility renovation program. The company’s goal to renovate more than 700 U.S. Ford Motor Company branded facilities during the next few years presented a tremendous opportunity for green technology implementation within the dealer network.

Ford is not the only car company with sustainable dealership initiatives. Nissan Green Shop Activities include various environmental efforts that take place at Nissan Motor dealerships across the globe, including reducing waste, recycling, and energy saving endeavors. The program was introduced in April 2000 as an environmental management system for all Nissan dealerships.

Something that dealerships in these programs implemented is energy-efficient lighting, which provides one of the quickest paybacks.

Funding assistance
Recently, many dealers moved quickly to take advantage of the Internal Revenue Service (IRS) Section 179D tax incentive, which expired last year. This is the section of the tax code that provided a benefit for businesses, architects, engineers, and contractors when they built or renovated an energy-efficient building.8

If the building project did not qualify for the maximum Energy Policy Act (EPAct) $1.80 per square foot immediate tax deduction, there were tax deductions of up to $0.60 per square foot for each of the major building subsystems—lighting, heating, ventilation, and air-conditioning, and the building envelope.9

Utility companies around the country are encouraging these efforts by offering energy-efficient lighting upgrade and replacement rebates, some of which cover up to 50 percent of installation costs for retrofits. Most utility rebate programs are offered on a first-come, first-served basis until funding is exhausted or the program is discontinued, so it is important for customers to get applications in early.

There are two types of utility rebate programs:

  • prescriptive rebates offer a fixed, predetermined dollar amount for each fixture replaced; and
  • custom rebates are based on the total energy savings of a specific lighting retrofit.

Custom rebate programs offer payments for both actual energy savings (kilowatts saved per hour) of upgrading to more efficient lighting technologies and reductions in peak demand (kilowatts) achieved in the first year after implementation.

Prescriptive rebates, however, do not account for the energy savings gained by reducing the number of fixtures through a redesign. Utilities in almost every state offer some rebates for light emitting diode systems. Details on these programs are aggregated in the federal DSIRE database and individual utility sites.10

The photos to the left show Gary Force Toyota’s lot after the replacement. The installation of LED luminaires enhances the appearance of the vehicles. The new exterior lighting allows the dealership to decrease operating expenses.

This photo shows Gary Force Toyota’s lot after the replacement. The installation of LED luminaires enhances the appearance of the vehicles. The new exterior lighting allows the dealership to decrease operating expenses.

Energy-effi cient LED area lights transform Gary Force Toyota’s parking lot and are virtually maintenance-free.

Energy-efficient LED area lights transform Gary Force Toyota’s parking lot and are virtually maintenance-free.










LEDs in action
Established in 1973, family-owned Gary Force Toyota is part of three award-winning auto dealerships. Based in Bowling Green, Kentucky, the dealership is committed to incorporating sustainable products into the facilities.

Exterior luminaires
As a long-established business, the owners and management team knew they could make a strong environmental statement while also attracting customers. Car dealership lots use a tremendous amount of energy and install many light fixtures to illuminate the cars outside at night.

Gary Force Toyota sits on a 0.8-ha (2-acre) lot with a 210-car inventory, and an 1858-m2 (20,000-sf) showroom and repair shop. The dealership recently replaced 63 of the old 1000-W metal halide fixtures in the exterior lot with the same number of 240W LED luminaires. The dealership also replaced six 250W metal halide wall packs with six 60W LED wall packs.

The impetus for the LED retrofit was the dramatic energy savings. Previously, the dealership was spending almost $30,000 annually on utility costs, however, with the new luminaires, their energy costs will be reduced to approximately $6620. Additionally, every three months, about

12 of the metal halide fixtures needed maintenance, costing $26,400 in maintenance over five years. Now, the new LED luminaires are virtually maintenance free with a five-year warranty.

After seeing the product, learning about the energy savings—greater than 70 percent over the metal halide—and determining the dealership would have just a two year return on investment (ROI) on the LED lights, it was an easy decision. The Tennessee Valley Authority also provided an incentive of $21,700 for upgrading the fixtures to LED.

The LED luminaires provide consistent light levels, reduce hazardous waste disposal, and provide dramatically more efficient light distribution than the metal halide fixtures.

“The new exterior LED lighting allows us to drive down operating expenses, present our cars in the best light, and contribute to the greening of our community,” said Dave Stumbo, owner and vice president/general manager.

Both employees and customers have noticed the bright, white lights and have commented about how much easier it is to see the cars, anywhere in the lot.

“We installed the LED luminaires because they pay back in so many ways,” continued Stumbo. “Additionally, we are so impressed with how well these LED luminaires are performing at Gary Force Toyota we upgraded the exterior lighting at our Acura pre-owned dealership in Franklin, Tennessee.”

Additionally, the lights did not disturb surrounding businesses or residential areas. Many LED fixtures are designed for full cut-off. This means little to no light is emitted above the horizontal plain, therefore minimizing light pollution. To curtail light trespass (i.e. light extending beyond property lines and other boundaries) it is important to use fixtures with the right distribution patterns for the required area.

There are numerous factors contributing to dealerships’ sustainability efforts, such as manufacturers’ national initiatives, consumers’ increased concerns about environmental issues.

An environmentally conscious car dealership seems to be contradictory term. However, the bottom line is that by living and working sustainably dealerships can reduce energy costs, increase their brand/dealership’s recognition, and attract more customers.

Renovations such as LED lighting retrofits or the installation of light-emitting diode luminaires uring new construction are an excellent way for car dealerships to begin achieving their sustainability objectives.

1 For more, visit (back to top)
2 See E Source Customer Direct’s “Managing Energy Costs in Auto Dealerships” at (back to top)
3 See note 1. (back to top)
4 Visit Auto Remarketing’s “NADA Encourages Dealers to take Survey on Energy Use,” article at (back to top)
5 For more, see “Unlocking Energy Efficiency in the U.S. Economy” at (back to top)
6 For more, see Matthew Wheeland’s “For Expands Efficiency Efforts to its Dealers’ Lots,” at (back to top)
7 For more, visit (back to top)
8 For more, see Dean Zerbe’s article, “179D Tax Break for Energy Efficient Buildings—Update,” at (back to top)
9 See Charles R. Goulding, Charles G. Goulding, and Rachelle Arum’s article online at Dealers Move Quickly to Complete Tax Incentive LED Lighting Projects.pdf. (back to top)
10 To access the database visit (back to top)

Jeff Gatzow is national sales and marketing manager, lighting with Optec LED Lighting. He has worked in the LED luminaire industry for over 10 years, and prior to this he worked in the illuminated signage/brand identity industry. Gatzow can be reached by e-mail at

A Look at Cool Roof Options

All photos courtesy Viridian Systems

All photos courtesy Viridian Systems

by Ron Utzler

Within the built environment there are many avenues to energy savings. The energy efficiency of a building is affected by everything from lighting and windows, to insulation and reflective roofing. This article focuses on low-slope roofing materials that represent reflective roofing options.

Reflective roofing is typically a method of using light-colored surfacing that reflects more of the sun’s heat than it absorbs. A reflective value is the portion of light reflected, measured from 0 to 1, with higher values representing cooler surfaces. These values are measured with sophisticated, calibrated equipment under controlled conditions.

Providing roofs with a reflective surface is not a new concept. For example, asphalt coatings with leafing aluminum pigment have always promoted the benefit of reducing interior temperatures while slowing the oxidation of the waterproofing membrane. This reduces the load of air-conditioning systems and improves the occupant’s comfort, while extending the service life of the roof membrane.

However, the term ‘cool roofing’ was more recently coined with the increased focus on the reduction of energy consumption. As with any movement, there are opportunities for entrepreneurs to provide support and related services. Everything from third-party testing laboratories to new programs for certification have been evolving.

There are federal

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agencies, for example, that have decided all roofing in certain regions must meet Energy Star’s cool roofing requirements. The U.S. Environmental Protection Agency (EPA) established the voluntary Energy Star program which requires a roofing membrane to have an initial reflectance of .65 and a three-year-aged reflectance of .50 to be considered Energy Star rated. So, design teams should consider available roofing options in compliance with cool roofing requirements.

Cool roof systems are beneficial in climates where a building’s interior requires more cooling days, as opposed to heating days. Whether the goal is to reduce energy cost or improve the environment, building owners and specifiers must make educated decisions about roofing needs. To still have a cool roof, they need to be familiar with the available options, along with advantages, disadvantages, and cautions. This article contains a general overview of the low-slope roof system categories that can be installed with at least the initial reflectance to be considered a cool roof.

A fully adhered modifi ed-bitumen (mod-bit) membrane is being installed with hot asphalt. The worker at the left is ‘sugaring’ loose granules into the asphalt at seams to produce a uniform refl ective fi nish.

A fully adhered modified-bitumen (mod-bit) membrane is being installed with hot asphalt. The worker at the left is ‘sugaring’ loose granules into the asphalt at seams to produce a uniform reflective finish.

A white polyvinyl chloride (PVC) single-ply membrane provides a highly refl ective, cool roofi ng assembly.

A white polyvinyl chloride (PVC) single-ply membrane provides a highly reflective, cool roofing assembly.










Single-ply membrane systems
As the name indicates, single-ply membrane assemblies are synthetic sheets in various combinations of compounds with or without reinforcement options, and installed in a single layer held in place by mechanical fasteners, adhesives, or some form of ballast. Most, if not all, of these membranes are available in white, and will provide the reflectance required to be considered a cool roof. Naturally, to take advantage of this reflectance, the membrane will either be adhered or mechanically fastened. A ballasted system may still qualify as a cool roof, depending on the color of the ballast itself.

Advantages of this assembly include:

  • application of one membrane will generally result in lower material and labor cost;
  • these membranes are typically available in bright white and their smooth surface provide the highest level of reflectance;
  • non-ballasted applications result in a smooth surface generally easier to visibly locate leak sources caused by defects or damage; and
  • in many cases, these membranes are manufactured with a gloss finish or clear film to provide a surface that resists dirt pickup, providing a self-cleaning attribute that can help maintain higher reflectance over time.

A disadvantage of this roof type is a single layer of waterproofing is more vulnerable to physical damage, resulting in wet insulation and interior leaks, depending on the deck type. For example, a structural concrete deck can hold more water in the system above the deck before it builds up to a break in the deck, allowing water to leak into the building. Unfortunately, this can cause more insulation damage from a single puncture because the leaks may go undetected until water enters the building’s interior. Of course, this concern for an unknown leak is based on the deck type and therefore applies to all systems, once the membrane’s waterproof integrity is broken.

Additionally, the anticipated useful life of a single-ply membrane is generally considered less than multiple-ply assemblies. This is most often viewed as an attribute of the mass (thickness) of the waterproofing membrane, which decreases over time by oxidation.

The amount of traffic on the membrane surface will also add a wear factor. Strategically placed walk treads helps can help.

When specifying these systems, it is important to keep in mind the membranes can be extremely slippery when wet. Further, because they are white means rainwater, dew, frost, and snow will be slower to evaporate. If someone is required to spend any length of time on a white membrane on a sunny day, wearing sunglasses is important.

Design teams should also be aware some membranes may have a short history of service in their current formulation. If a formula is changed to address a newly discovered performance issue, the alteration could produce a completely different, unanticipated problem after real exposure.

The local conditions of a particular roof exposure must also be considered. For example, if the roof will be exposed to chemical fallout from a manufacturing process, the chemical content and concentrations involved must be determined, so a membrane with the best resistance to those exposures is specified. The membrane supplier should be able to provide a chemical resistance chart for its product.

The photos above show a completed built-up roofi ng (BUR) system and light-colored gravel assembly.

The photos above show a completed built-up roofing (BUR) system and light-colored gravel assembly.










Modified bitumen membrane systems
The modified-bitumen (mod-bit) membrane systems include sheet membranes made with asphalt typically modified with rubber or plastic compounds and reinforced with either glass or polyester mats. Typically, the surface ply is manufactured with light-colored mineral granules embedded.

Historically, these granules typically provided an initial reflectance value of .25 to .27 on a scale of 0 to 1. However, as the drive for energy savings grew, manufacturers developed brighter granules, or other methods to increase the product’s reflectivity. Some of these methods include the embedment of other synthetic white chips, rather than granules, or factory-coating the sheet with a brighter white coating.These brighter versions have raised the reflectance values to .70 to .80.

Such systems emerged in the United States in the 1980s after years of use in Europe, and have grown in popularity. Originally, the asphalt-based systems seemed a natural progression for contractors who were used to installing hot-applied built-up roofing (BUR) systems. They have reached a level of development where they are dependable membranes that also provide redundancy of plies.

Advantages of the mod-bit membrane systems are that they are typically installed in hot asphalt, cold-applied adhesive, heat welding or self-adhered, providing various options for the project’s needs. For example, getting hot asphalt to the top of a high-rise building may not be practical, but pails of cold-applied adhesive can be delivered to the roof. Also, maintenance and minor repairs can generally be completed with readily available asphalt materials.

An important attribute to the surface’s performance, the granulated membrane refers to the quality of the granule embedment. This is a key standard of quality that will determine how long the membrane weathers and wears before the mineral granules are dislodged and accumulate in the gutters and drain sumps. Referring to ASTM D4977/6164, Standard Test Method for Granule Adhesion to Mineral-surfaced Roofing by Abrasion, granule loss should not be greater than 2 grams. This value is not always reported in manufacturer’s product data sheets, but it is still an important feature to compare during the membrane selection process.

The consistency in granule color is not always able to be maintained by manufacturers. Slight variations from one production lot to another can show up on the same roof, leading to an inconsistent appearance in a finished project.

Since these systems are typically adhered with asphalt adhesives, it depends on the applicator’s expertise to avoid the unsightly appearance due to tracking the adhesive onto the finished surface, or uncontrolled bleed-out of adhesive at membrane laps. While the embedding of extra granules in the bleed out during application and applying white coating to tracked adhesive is often effective in providing a good finished appearance, this author is a proponent of post-coating the completed installation.

Due to the inconsistent shades of white previously mentioned and application aesthetics, the added initial cost to the project for the application of a quality acrylic elastomeric coating system can provide both immediate, and long-term benefits. It gives the immediate benefit of uniform appearance and maximum reflectivity, with the long-term advantage of an extended service life of the membrane. Even if the owner elects not to periodically recoat the surface, the initial coating can provide an additional five or more years of service as a sacrificial surfacing in the roof’s lifecycle.

The wide variety of membrane reinforcements and coating compounds means determining the right membrane for the given conditions will need to be an important aspect of the specification process. Design teams should factor in the anticipated amount of foot traffic on the roof system and include walk treads as a design element.

This highly refl ective fl eece-backed PVC is being fully adhered over a multiple ply asphalt BUR and seams are heat welded with an automatic hot-air welder.

This highly reflective fleece-backed PVC is being fully adhered over a multiple ply asphalt BUR and seams are heat welded with an automatic hot-air welder.

After coating a new modifi ed-bitumen membrane with white elastomeric coating provides a dual purpose—it provides a clean, uniform Energy Star system and adds fi lm thickness to extend the system’s service life.

After coating a new modified-bitumen membrane with white elastomeric coating provides a dual purpose—it provides a clean, uniform Energy Star system and adds film thickness to extend the system’s service life.













Built-up roof systems
As the name implies, built-up roofing (BUR) systems are assembled on the roof using multiple plies of reinforcement built-up with bitumen interply adhesives. Traditionally, BUR systems are surfaced with a flood coat of bitumen into which gravel is imbedded. While BUR is the oldest system, with a history long-term performance, it has fallen into disfavor with the rise in popularity of reflective cool roof systems. However, there are bright white gravels available for surfacing enabling the traditional BUR to qualify for cool roof status.

There has also been a rise in popularity in what is referred to as a ‘hybrid’ system. This combines the redundancy of reinforcement plies of BUR with the white granule surfacing of a mod-bit cap sheet. Traditional BUR with gravel provides a time-proven, durable system with a long lifecycle. Further, the gravel surface and number of plies provide traffic and puncture resistance.

Some disadvantages to these systems can include objection to the odor of hot bitumen at the project site and the ensuing potential complaints from the building occupants. However, there are fume-recovery equipment options, and there are cold-applied adhesive systems available.

In some high wind regions, gravel roofs may be resisted due to potential of gravel becoming projectiles. While this is a real concern for single-ply ballasted (i.e. loose-laid) roofs, the smaller gravel used to surface BUR roofs is typically adhered.

BUR roofs with gravel will generally weigh more than other membrane types, so the decks should be verified as capable of bearing the weight. If using hot asphalt or even cold adhesives, the surroundings and building occupancy should be taken into account and require a fume recovery or afterburner kettles for hot asphalt. Additionally, air intake vents should be covered during application.

With an ambient temperature of 27.7 C (82 F), note the surface temperature difference between a black surface (A), a standard granule surfaced modifi ed-bitumen (B), and a granule modifi ed-bitumen with an elastomeric white coating surface (C).

With an ambient temperature of 27.7 C (82 F), note the surface temperature difference between a black surface (A), a standard granule surfaced modified-bitumen (B), and a granule modified-bitumen with an elastomeric white coating surface (C).

SPF systems
Sprayed-in-place polyurethane foam (SPF) systems combine two chemical components—isocyanate and resin—through specialized spray equipment. As the resulting liquid is applied to a substrate, it will expand 20 to 30 times its volume to form insulating polyurethane foam. The foam is generally applied in multiple passes of the spray gun resulting in layering 12.7 to 38 mm (½ to 1 ½ in.) per pass (or ‘lift’). A good applicator can control the lifts and construct a uniform taper to drains for proper water drainage.

Applications of SPF need to be surfaced to protect it from ultraviolet (UV) degradation, and to provide waterproofing, along with protection from physical damage and fire resistance.

The most typical surfacing is white elastomeric coating. A foam application is considered monolithic, as opposed to individual rigid insulation boards. This would reduce stress on the waterproofing membrane which could occur at the joints of rigid insulation.

Sprayfoam applications are considered self-flashing since each pass can be completed with a continuous movement from horizontal to vertical substrate. This reduces the chances of detailing errors in critical areas of stress.

The expertise of the applicator is crucial to the success of SPF systems. For example, if the component mixing is off ratio, the resulting foam would have different performance properties pertaining to rigidity or softness. Weather conditions during application are also crucial because of the way these products react to moisture. This can affect the foam’s surface texture, making effective coating application more difficult.

As demonstrated here, there are numerous roof systems that can qualify for cool roof ratings. The building owner’s individual needs and conditions will affect how the best system is selected.

It is important to keep in mind that no matter which roof system is selected; it will not perform as expected unless there is a proper evaluation of needs versus options, along with the appropriate budget. Additionally, detailed specifications with project-specific predesigned details need to be included. Finally, the installation should be contracted to a qualified applicator having experience with the specified system.

Ron Utzler has been involved in the technical aspects of commercial roofing systems for 35 years. He is currently technical director at Viridian Systems in Tallmadge, Ohio. Utzler can be reached by email at

Saving on Natatorium Energy Costs with Green Options

Photos courtesy Jarmel Kizel Architects and Engineers

Photos courtesy Jarmel Kizel Architects and Engineers

by Ralph Kittler, PE

When it comes to designing indoor swimming pool facilities, it is critical to ensure not only a healthy interior environment, but also energy efficiency. New technologies can provide both optimal natatorium environmental control and curtail utility consumption when specified.

Commercial dehumidifiers and 100 percent outside air ventilation system (OAVS) technology for indoor pools have significantly changed in the last decade. Consequently, a new or retrofitted natatorium HVAC system can potentially save millions of dollars in energy costs over the equipment’s 15 to 25-year lifecycle, depending on the sustainable options specified.

In short, today’s indoor pool HVAC equipment is not your parent’s dehumidifier. Current systems can come with:

  • reduced refrigerant charges of up to 85 percent;
  • lowered fan energy costs;
  • compressor heat recovery for ‘free’ pool-water-heating;
  • exhaust heat recovery for preheating outdoor air;
  • modulating controls for pinpoint temperature and humidity control;
  • glycol heat rejection to dry coolers; and
  • web-based microprocessor monitoring and alarms for maintaining daily pinpoint, real-time control by factory technicians.
In New Jersey, the Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center depends on its dehumidifi er to keep glass shared by the aerobics and aquatic areas free of condensation.

In New Jersey, the Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center depends on its dehumidifier to keep glass
shared by the aerobics and aquatic areas free of condensation.

The design team kept the aquatic center a focal point at HUMC Fitness and Wellness Center with ample use of glass separating it from the other areas.

The design team kept the aquatic center a focal point at HUMC Fitness and Wellness Center with ample use of glass separating it from the other areas.









The R-22 ban and dehumidifier retrofits
Thousands of units manufactured after the 1970s’ advent of the modern-day mechanical indoor pool dehumidifier will be reaching the end of their useful lifecycle within the next five years.

Most of these aging dehumidifiers operate using the hydrochlorofluorocarbon (HCFC) refrigerant R-22. According to the 1989 international treaty, Montreal Protocol on Substances that Deplete the Ozone Layer, this refrigerant has ozone-depleting potential. As a result of the treaty, R-22 is amid a world-wide manufacturing phase-out. The phase-out—which currently calls for 90 percent next year and 99 percent in 2020—has already spiked prices due to dwindling supplies. Price volatility is demonstrated by contractor charges ranging anywhere from $35 to more than $100 per pound of R-22.

Conventional natatorium dehumidifiers built during last 25 years can range from 45 kg (100 lb) to more than 317.5 kg (700 lb) of refrigerant. Therefore, a dehumidifier that leaks all, or even a substantial portion, of its R-22 refrigerant charge could represent significant cost for refrigerant replacement, not to mention damage the environment. This fact alone should get natatorium owners’ attention. However, the fact a refrigeration circuit will generally have at least one or two refrigerant leaks during its lifecycle should also be considered.

R-410A is the succeeding refrigerant to R-22. It is a less environmental-damaging hydrofluorocarbon (HFC)—due to its lack of chlorine—and used in most new dehumidifiers over the last five years, but it is also expecting a future phase-out and subsequent price increase.

Refrigerant price volatility, as well as the suspected danger to the environment, has prompted many HVAC manufacturers to look toward alternatives, such as substituting up to 85 percent of the refrigerant with glycol for heat rejection. Glycol is significantly less toxic to the environment. It operates under pump pressures versus the high pressures of compressors and refrigerants; thus, it is less likely to leak—when it does, glycol is not a vapor or ozone-depleting chemical.

The glycol-based units still have a small refrigerant charge of typically 10 to 20 percent of conventional dehumidifiers. These refrigeration circuits are necessary for dehumidification and optional natatorium space-cooling, however, they carry dramatically less leak liability and risk because they are ultra-compact and factory-sealed by expert technicians. The glycol is transported through polyvinyl chloride (PVC) piping to dry coolers for heat rejection. It also eliminates the potential of installation errors involving hundreds of pounds of refrigerant, expensive copper piping, and outdoor air-cooled condensers subject to contractor onsite workmanship.

In New Jersey, the new $24-million Hackensack University Medical Center’s (HUMC’s) Fitness and Wellness Center Powered by the Giants, employs a 70-ton, 23,000-cfm dehumidifier that uses 80 percent less refrigerant to dehumidify its 743-m2 (8000-sf) aquatic space. The dehumidifier substitutes glycol for the estimated 312 kg (690 lb) of R-410A refrigerant used by a similar-sized conventional dehumidifier. Specified by consulting engineer firm, Jarmel-Kizel Architects and Engineers, the 10,405-m2 (112,000-sf) facility’s step toward refrigerant independence complemented HUMC’s sustainable programs, such as its in-house Dierdre Imus Environmental Health Center—a not-for-profit children’s advocacy group dedicated to identifying, controlling, and preventing environmental toxic exposure.

The HUMC’s dehumidifi er’s use of glycol for heat rejection eliminated hundreds of pounds of refrigerant from the center. Compared to refrigerants, glycol is 95 percent less expensive and minimally environmentally-damaging in the event of a leak. Photos courtesy Seresco Technologies

The HUMC’s dehumidifier’s use of glycol for heat rejection eliminated hundreds of pounds of refrigerant from the center. Compared to refrigerants, glycol is 95 percent less expensive and minimally environmentally-damaging in the event of a leak. Photos courtesy Seresco Technologies

Direct-drive plenum fans connect the motor directly to the fan shaft, thus eliminating friction, noise, maintenance, and power transfer ineffi ciencies associated with traditional belt-driven fans. As a result, a direct drive plenum style fan uses considerably less energy.

Direct-drive plenum fans connect the motor directly to the fan shaft, thus eliminating friction, noise, maintenance, and power transfer inefficiencies associated with traditional belt-driven fans. As a result, a direct drive plenum style fan uses considerably less energy.


Retrofitting natatoriums
Whether it is an indoor pool for a small hotel or a large community center, specifiers should prepare for the coming deluge of the aforementioned dehumidifiers that will need replacement in the coming years.

A drop-in replacement with today’s technological improvements might appear feasible on paper, but the reality of mechanical room access may not accommodate a machine that is 2.4 x 3 x 9.1 m (8 x 10 x 30 ft) and arrives at the jobsite on a semi-truck flatbed trailer.

This was a situation confronting Ottawa-based consulting engineer firm, Goodkey Weedmark & Associates in nearby Kanata, Ont., during a $500,000-retrofit of the 25-year-old conventional indoor city recreation center into the new Kanata Leisure and Fitness Centre Wave Pool (KLFCWP).

The firm specified one large 2.6 x 3 x 7.3-m (8.5 x 10 x 24-ft) custom-manufactured unit, which was able to fit into a small mechanical room with no shipping door access thanks to a mechanical room’s mezzanine-level large exterior wall outdoor air louver. The dehumidifier manufacturer pre-planned the custom-built unit for breakdown into three 2.4-m (8-ft) long sections for shipping after the factory assembled and tested it under simulated natatorium operating conditions.

Mechanical contractor, T.P. Crawford (Gloucester, Ont.), rigged the three sections through the outdoor air louver, which was enlarged to 2.8 x 3-m (9.1 x 9.8-ft) for more access. The contractor then assembled and installed it inside the mechanical room. The louver’s opening then refitted for a new outdoor air damper/louver to comply with American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 62, Ventilation for Acceptable Indoor Air Quality—the standard’s outdoor air rates that had increased since the original building’s construction in 1986.

Instead of unit breakdown and assembly inside the mechanical room, a less-expensive and more reliable solution for cramped access and space in mechanical rooms has been developed. The solution is modular units designed to fit through 812-mm (32-in.) wide door frames. Once dollied into the mechanical room, the small horizontal footprint modular units are stacked and connections are quickly integrated to operate in tandem. Multiple pairs can equal the capacity of large units, but they consume considerably less floor space of large original dehumidifiers.

While they are mainly a logistics benefit and designed for retrofitting, the redundancy of two compressors, two coils, and two fans also offer energy-efficient staging that the larger unit with one compressor could never achieve. For example, during low-occupancy periods, staging off one of two small compressors instead of operating one large compressor sized for full occupancy can be a significant energy-savings.

Part of a retrofi t that netted the Wulf Recreation Center in Evergreen, Colorado, a 32 percent energy reduction under an energy performance contract, this replacement outdoor air ventilation system saves nearly $5000 in operational costs. Photos courtesy Wulf Recreation Center

Part of a retrofit that netted the Wulf Recreation Center in
Evergreen, Colorado, a 32 percent energy reduction under an energy performance contract, this replacement outdoor air ventilation system
saves nearly $5000 in operational costs. Photos courtesy Wulf Recreation Center

The Wulf Recreation Center’s new outdoor air ventilation system, does not use compressors, but does take advantage of Colorado’s dry, cooler mountainous climate to provide ideal indoor air quality to the pool. The system uses several state-of-the-art technologies including heat recovery, direct drive fans, and an on-board microprocessor controller.

The Wulf Recreation Center’s new outdoor air ventilation system, does not use compressors, but does take advantage of Colorado’s dry, cooler mountainous climate to provide ideal indoor air quality to the pool. The system uses several state-of-the-art technologies including heat recovery, direct drive fans, and an on-board microprocessor controller.














Considering outdoor air ventilation systems
Another sustainable consideration for either retrofits or new construction is an OAVS instead of a mechanical dehumidifier; however, the former is only viable in drier, cooler climates, such as mountainous regions or the northern United States. Using outdoor air in these geographical regions can reduce operating costs significantly, versus continually conditioning air with more energy-intensive compressor-based mechanical refrigeration circuits to maintain a natatorium’s desired 82 to 85 F (27.7 to 29.4 C) space temperature and 50 to 60 percent relative humidity (RH).

What make OAVS more conducive today versus a decade ago are many recent technology and control advancements combined with code changes mandating higher minimum amounts of outdoor air for indoor air quality (IAQ) reasons.

For example, today’s technological advancements were one of the reasons energy performance contractor, McKinstry in Seattle, Washington, was able to guarantee a 32-percent reduction as part of the retrofit of the 40-year-old Wulf Recreation Center in Evergreen, Colorado. The 3716-m2 (40,000-sf) center’s $540,000 retrofit—which included lighting, building envelope insulation, and digital controls—is saving the center $18,000 annually. New state-of-the-art indoor pool ventilation garners a significant portion of the savings. The two 6500-cfm outdoor air ventilation replacement systems for the 650-m2 (7000-sf) indoor pool is now saving a minimum of $4995 in operational savings and $12,704 in reduced therms annually, versus the former original gas-fired make-up air system, according to utility bills for the facility and an energy review McKinstry performed as part of its energy performance contract.

Integral to the savings are the two units’ heat recovery, direct drive fans, and an on-board microprocessor controller for pinpoint outdoor air modulation. Unlike the original supply/exhaust system, heat from the space’s exhaust air is now recovered via a glycol run around loop (GRAL) for pre-heating outdoor air. Using heat recovery helps raise outdoor air temperatures from –17.7 to 7.2 C (0 to 45 F) and reduces heating costs significantly.

As the Wulf Recreation Center demonstrates, an OAVS indoor swimming pool environment can be precisely controlled for much of the year, due partly to the technology advancements of outdoor air modulation controls.

While a well-designed OAVS can provide precise space conditions during drier, colder outdoor weather, this approach is not suitable for every facility. This is because there are periods when the space conditions may become warmer and more humid than desired, such as during mild weather and summer. For facilities where this period of time is short, or where the patrons would not mind elevated conditions during the warmer weather as a trade-off to the higher operating costs of running and maintaining a refrigeration circuit, OAVS is definitely a viable, sustainable option.

Whether an indoor pool is a prime candidate for the OAVS approach can be determined by software available from most dehumidifier manufacturers. The software calculates and models the expected space conditions throughout the course of a year, using local weather data input.

The use of outdoor air-modulating controls is another advantage of the new HVAC technology at the Wulf Recreation Center. By monitoring indoor and outdoor air conditions precisely, only the required amount of outdoor air is introduced to maintain the best possible pool space indoor air quality (IAQ), save energy, and comply with codes. Photo courtesy McKinstry

The use of outdoor air-modulating controls is another advantage of the new HVAC technology at the Wulf Recreation Center. By monitoring indoor and outdoor air conditions precisely, only the required amount of outdoor air is introduced to maintain the best possible pool space indoor air quality (IAQ), save energy, and comply with codes. Photo courtesy McKinstry

The dehumidifi er industry has innovated new designs featuring up to 85 percent less refrigerant than a traditional dehumidifi er. Instead of refrigerants and copper piping, the process uses glycol, heat exchangers, and polyvinyl chloride (PVC) piping, which signifi cantly reduces the environmental impact. Photo courtesy Seresco Technologies

The dehumidifier industry has innovated new designs featuring up to 85 percent less refrigerant than a traditional dehumidifier. Instead of refrigerants and copper piping, the process uses glycol, heat exchangers, and polyvinyl chloride (PVC) piping, which significantly reduces the environmental impact. Photo courtesy Seresco Technologies











Specifying high technology
The real game-changer in indoor pool HVAC energy savings has come with technology such as exhaust-air heat-recovery, dedicated duty direct drive fans, and microprocessor operational control and monitoring.

Perhaps the most energy-saving air comfort and efficiency development has been the modulating outdoor air control. These controls monitor indoor and outdoor air conditions precisely and introduce only the amount of outdoor air required to maintain the best possible indoor air conditions. Before these precise controls were developed, natatoriums might have provided more outdoor air than needed during ultra-dry winter conditions that resulted in indoor relative humidity (RH) levels dropping too low below the desired 50-percent RH. Low RH levels create an uncomfortable chilling effect on wet skin and also raise operational costs. Bringing in more outdoor air than needed results in more outside air and pool water heating requirements.

Another option is pool water heating via heat recovery from the refrigeration circuit’s compressors. However, the ‘free’ pool water heating option is sometimes omitted during product specification, especially in value engineering requests. It is also sometimes missed during contractor installation.

There are dozens of dehumidifiers currently operating in natatoriums throughout North America where this energy-saving feature is mistakenly bypassed unbeknownst to the building owner. Consequently, the facility needlessly pays for pool water heating via a separate conventional gas-fired or electric pool water heater originally intended to back-up the dehumidifier’s pool water heating or expedite it during a dump-and-fill.

Selecting a mechanical dehumidifier with pool water heating through heat recovery might raise the upfront capital cost, but the benefit over the long-term will result in thousands of dollars saved in energy costs, depending on the facility size.

ASHRAE 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, has taken the energy recovery requirement a step further by mandating heat recovery or a pool cover. Many states have adopted the standard into local code requirements.

ASHRAE 90.1 calls for a pool cover for commercial indoor pools using conventional pool heaters unless “over 60 percent of the energy for heating comes from site-recovered energy.” The pool water heating option for a compressorized unit easily satisfies this requirement, but could also help satisfy a local code requirement and help eliminate the need for a pool cover.

Using exhaust air to pre-heat outdoor air
ASHRAE 62, Standards for Ventilation and Indoor Air Quality, recommends all commercial buildings bring a prescribed percentage of outdoor air as mandated by local building codes.

For the northern United States and Canadian indoor pools, wintertime heating of cold outdoor air to at least 26 C (80 F) to match the pool air temperature is costly. Fortunately for natatorium operators, their facilities’ humid and warm exhaust air is extremely energy rich and ideal for energy recovery. This recovered energy can be used to preheat the code-required outdoor air via heat-exchangers.

Preheating outdoor air using recovered heat from the exhaust air can cut outdoor air-heating costs by 50 to 75 percent. The payback for this kind of pool dehumidifier option is often only a few months (and rarely more than a few years), which makes it a cost-effective investment.

Remotely located exhaust fans can also be outfitted with heat transfer coils piped to the dehumidifier. Natatorium exhaust air is an energy source specifiers and operators should always consider for heat recovery. Aging dehumidifiers manufactured before this feature was available should be reviewed for a more energy-efficient replacement.

Direct drive plenum fans with VFD
Another example of a new energy savings technology is the introduction of dedicated duty direct-drive plenum fans with variable frequency drives (VFD). These plenum fans are a different style of fan that delivers air more efficiently than the traditional centrifugal-style typically seen in traditional dehumidifiers.

Compared to traditional belt-driven fans, a direct-drive plenum fan with a VFD can amount to as much as 15 percent in fan motor energy reduction. Considering a pool dehumidifier’s fans typically operate 24/7, the savings over the equipment’s lifecycle can be significant. The payback is instantaneous since direct-drive plenum fans with VFDs have comparable price to belt-driven systems.

Unlike belt-driven fans, the direct-drive concept connects the motor directly to the fan shaft. Thus, it eliminates friction, noise, maintenance, and power-transfer inefficiencies associated with belt drives.

Remote monitoring
All the aforementioned energy-saving technologies are worthless unless they stay well-tuned, maintained, and monitored. Unmonitored systems can limp along well below their intended optimal operating conditions, unbeknownst to the building owner.

Some dehumidifier manufacturers have solved this dilemma with the development of on-board monitor/control microprocessors that can send the entire unit’s vital operating statistics to the factory via the Internet. These programs sometimes offer a free daily monitoring service and even have smartphone applications where an authorized user can get e-mail alerts or access a unit from anywhere. The manufacturer can alert the facility manager of any issues and help the local service contractor troubleshoot, set up, or adjust the unit to ensure optimal performance. In the event of an alarm, troubleshooting can be assisted by a factory engineer, which ensures a quick resolution to any problem.

Many of the aforementioned advancements in indoor pool dehumidification over the past decade are manufacturers’ catalog items, but they also must be understood and specified by the consulting engineers and contractors. Once the building is operating, specifiers as well as building owners can rest assured the facility is operating at an optimal efficiency and is using the least amount of energy possible in providing IAQ.

Ralph Kittler, PE, is a co-founder and vice president of sales/marketing at Seresco Technologies, an Ottawa-based manufacturer of conventional and reduced-refrigerant natatorium dehumidifiers, and outdoor air ventilation system natatorium HVAC systems. He has 24 years of experience in the HVAC industry and a degree in mechanical engineering from Lakehead University (Thunder Bay, Ont.). Kittler is an American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) Distinguished Lecturer and sits on the association’s Technical Committee 9.8 and 8.10. He can be reached via e-mail at

Seeing the Urban Forests for the Trees: Secondary benefits of our cities’ wood

Photo courtesy M MagazinePhoto courtesy M Magazine

by J. Gerard Capell, FCSI, AIA, CCS

A childhood treehouse, a place to hang a swing, or the support for a hammock in the cool shade—many of us can think back to these valuable memories that reflect the utility of trees in urban and suburban spaces. What if there were additional memories to be gained from the death and removal of those same trees? In a growing number of cities in the United States, urban forests are being recognized as a valuable, renewable resource for furnishings, paneling, flooring, or trim for residential or commercial spaces.

However, this transformation is neither straight forward nor simple. The process does not call for clear-cutting local parks—it involves the removal of trees that are diseased, storm-damaged, at the end of their natural lives, or need to be removed to make way for new development and street repairs.

Urban forestry is an industry resulting from the infestation of the emerald ash borer (EAB) that began in Michigan in 2002 and has now spread as far as Colorado, Georgia, and northeastern Canada. There are an estimated eight billion ash trees in the United States, and approximately 150 to 200 million have already died as a result of this invasive species.1 However, urban forestry is not limited to ash trees. In Milwaukee, the city cuts down and transports Norway maples, elms, honey locusts, basswood, and poplar—all of which are sent to a local mill for processing and are available for sale.

Emerald ash borers have been responsible for the felling of some 200 million trees. However, this wood could be repurposed in exciting ways. Photo © Leah Bauer, USDA Forest Service Northern Research Station

Emerald ash borers have been responsible for the felling of some 200 million trees. However, this wood
could be repurposed in exciting ways. Photo © Leah Bauer, USDA Forest Service Northern Research Station

City of Milwaukee workers loading a downed urban ash tree. Photo courtesy M Magazine

City of Milwaukee workers loading a downed urban ash tree. Photo courtesy M Magazine









Urban versus wilderness
Milwaukee is somewhat unique in that its department of forestry is responsible for cutting and trimming all city trees. The department can uniformly instruct the workers how to cut down the trees. The city also has a unique relationship with a local sawmill (Kettle Moraine Hardwoods), whose owner, Bob Wesp, has personally taught the workers how to look at a tree and keep in mind its usability as urban-cut lumber.

This might sound simple, but it is important to keep in mind the average city’s municipal employee is not a lumberjack from the Pacific Northwest with the skill and knowledge of how a mill will cut the tree into 1-by planks. For urban forestry, the first thing that needs to be done is to tell the workers the logs need to be as long as possible. Typically, tree service companies cut down trees into 915 to 1220-mm (3 to 4-ft) long logs that are small enough to fit into a Bobcat skip loader so they can be taken to the corporation yard where they will be ground into wood mulch. However, carpenters want trim that is at least 2.4 m (8 ft) long—preferably 3.1 to 3.7 m (10 to 12 ft) to eliminate mid-wall joints. Additionally, mills want a trunk or branch to be at least 254 to 305 mm (10 to 12 in.) in diameter for efficient sawing.

There are other things urban foresters must take into account. For example, by cutting too high up on the trunk or too close to the crotch of a pair of branches, one may unintentionally lose some really rich graining that will add a great deal of character to the planks. This is particularly the case for wood selected for furnishings where a unique grain pattern or coloration can make all the difference between just a piece of furniture and that special chair or table that can garner a higher price.

In regular forest-harvesting, the logs are placed on a 15 to 21-m (50 to 75-ft) tractor trailer. In urban forestry, a 25-m2 (30-cy) dumpster is the typical means of carrying the logs from the site to the mill, which means a log’s length is limited to a maximum length of about 7 m (21 ft) due to the dumpster’s length. The urban forester also needs a lift large enough to safely handle a 58 to 76-mm (20 to 30-in.) log that is 6.9 m (20 ft) long. Once the dumpster is full, it is transported to the mill.

tree crop

Emerald ash borer larvae scarring of the Cambrian layer. Photo courtesy

Rough-sawn and planed urban ash board. Photos courtesy J. Gerard Capell

Rough-sawn and planed urban ash board. Photos courtesy J. Gerard Capell















Meet the beetles
One of the first cities to undertake such efforts was Ann Arbor, Michigan, which was badly hit by the emerald ash borer. It is estimated that 7000 ash trees that lined its streets and yards were lost, and another 3000 were removed from the parks and surrounding nature areas, at a cost of at least $2 million. It is further estimated southeast Michigan lost upward of 30 million ash trees.2

EAB is believed to have come to the United States from Asia via packing crates and pallets. The beetle kills a tree by burrowing under the bark and depositing its larvae in the Cambrian layer, disrupting the tree’s ability to transport water from the roots to the leaves. Fortunately, the larvae do not damage the wood—this means if the tree is healthy and solid without rot or large splits, its lumber will be fine for higher-value uses.

The first method of EAB control was to clear-cut areas within 405 m (1320 ft) of the infested tree. Now, this radical surgery-management style is giving way to a controlled cut system such as that employed by Milwaukee in which insecticide is used to slow the EAB from destroying entire neighborhoods of trees, thereby giving the forestry department time to extend the devastation and tree replacement process out over a decade or more. The loss of so many trees within such a short time produced a significant volume of wood. Traditionally, such lumber was ground up for mulch, processed for bio-mass energy generation, or just sent to the landfill.

The Southeast Michigan Resource Conservation and Development Council (SEMIRCD) received a grant from the U.S. Department of Agriculture (USDA) to show there could be an economic benefit from the EAB problem and demonstrate markets for removed lumber.3 Through their efforts, numerous new markets for urban wood have been developed. For instance, an American Institute of Architects (AIA) Michigan award-winning project (Ann Arbor’s Traverwood Library) used reclaimed ash for flooring, wall panels, and ceilings. Structural columns utilized trees that were simply stripped and sealed leaving the scarred, rune-like patterns left by the chewing beetles.4 Similar efforts are now being employed in other cities, including Milwaukee.

Urban butternut (left) and urban red maple (right) sample panels.

Urban butternut (left) and urban red maple (right) sample panels.

Red Maple 1















From mill to shop
Once at the mill, a log may be set aside to dry, but because there might not be enough lumber to make up a pallet of one type, logs may have to wait until an adequate amount has accumulated. Unless there is a specific order for pieces of a specific size, a tree will be cut as ‘log-run,’ which is approximately 25 mm (1 in.)—or 4/4—thickness by random widths. This can be milled to 18-mm (3/4-in.) material that in turn can be used for most siding, flooring, and trim. Stair treads, mantels, and other special pieces need to be identified early so wider pieces with particularly good character can be cut at the same time. As this is log-run material, a pallet of lumber is not sorted or graded and the planks from a set of trees can range from FAS to No. 2 Common as defined by the National Hardwood Lumber Association (NHLA).

Another issue for urban lumber that is much more of a challenge is the greater likelihood that nails, wire, or bolts have been embedded in the tree. This means each log has to be magnetically scanned and cleared. Hitting even a small nail can ruin a blade, endanger workers, and result in downtime to make repairs. The mill operator in Milwaukee reported that from 30 to 35 percent of the urban trees it receives contain metal versus about two percent for trees coming from a standard forest preserve. They then have to pull those trees aside and search for the metal, and then remove it. If they cannot find the metal (or if there is too much of it), the tree may have to be discarded.

Once cut, hardwoods can take as long as 200 days to achieve 20 percent moisture content (MC) when just stacked with stickers (wood strips) between the planks. This is still a long way from the six to eight percent needed for interior use, so the wood must be put in a kiln, which takes two to four weeks to bring the wood to the desired moisture content. Then, the board can be shipped to a cabinet shop for fabrication.

If an owner or designer wants to use a particular stand of trees, the required time to turn those living trees into usable lumber for a carpenter or furniture-maker would be two to three months from the date of hewing the trees to have lumber stock ready to be milled into flooring, paneling, or trim. Most mills will have cut and dried urban lumber, but it is necessary to check to find out how much lumber is on hand so as not to delay the project.

Due to the need for a city to have a clear process to deliver its trees, most will probably have just one mill do the processing. Contractors and designers must connect with this firm, or work with another organization that has established a relationship with the mill to facilitate ordering and delivery. Groups such as Southeast Michigan Resource Conservation and Development Council in Michigan and Wudeward Urban Forest Products in southeast Wisconsin promote urban lumber use though education to the design and construction industry. More can be found on a state-by-state basis as businesses and cities look for an ecologically sound response to the losses in urban forests.

Once the lumber arrives at a cabinet shop, the real beauty of the wood emerges as the rough-sawn planks are trimmed, edged, and shaped into usable pieces. The hidden benefit of urban lumber starts to be realized at this time as richer colors and grain patterns emerge. However, since log-run lumber is not graded or sorted, splits, warping, and snapping at loose knots can easily claim upward of 50 percent of the lumber delivered from a pallet, adding to the cost to the fabricator in lost materials and time. The designer and owner may want to schedule a visit to the shop at this time to verify the design intent for the wood is being realized, especially when the piece is a feature element such as an entry wall or reception desk.

Urban ash trim at the University of Wisconsin–Milwaukee. Photographs courtesy Amy Hall

Urban ash trim at the University of Wisconsin–Milwaukee. Photographs courtesy Amy Hall










The green forest
Another clear benefit of using urban lumber is the ability to gain credits from sustainability programs. With the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program, credits can be easily claimed for Materials and Resources (MR) Credit 5, Regional Material Use.

MR Credit 7, Certified Wood, is a more problematic credit to obtain. The difficulty arises in the lack of an established recognition by the Forest Stewardship Council (FSC) of urban wood. At press time, FSC had announced there will be a motion offered at its General Assembly to be held in Seville, Spain, in the fall to ‘capture’ urban wood as part of the supply stream. Many issues will have to be resolved to establish the type of recognition, but this is a positive event that was not expected by many in the urban wood community for at least another three years.

The designer’s role through this process is that of educator and facilitator. They need to ensure the contractor (and the related subcontractors) is aware of this special product and that additional care may be required during bidding and fabrication. They also need to make certain owners are aware this unique, sustainable resource is available and can be an asset to the completed project. As mentioned, the designer needs to be much more hands-on to facilitate the proper use of the urban lumber. It is akin to working with a fine marble slab—the goal is to capture as much of the intrinsic drama and beauty possible from a natural and non-uniform material.

Specifiers have a key role in ensuring urban lumber is correctly specified and incorporated in the project. Typical sections that would be used are MasterFormat 06 20 00–Finish Carpentry, 06 41 00–Architectural Casework, and 09 64 00–Wood Flooring. A small but important addition to a standard master specification should be a brief definition such as:

Urban Lumber: Wood that is obtained from trees located in cities, towns or suburbs not harvested for their timber value, but removed because of insect, disease or circumstance.

This will help clarify the material, distinguishing it from salvaged lumber, which may be collected from an existing building, or from rivers and lakes.

This an example of urban ash stair treads.

This an example of urban ash stair treads.

Other key areas should be inserted into a specification section depending on the level of desired aesthetic control. They include:

  • samples of adequate size and length to show the range of acceptable color, grain, and acceptable flaws;
  • pre-fabrication meeting, where the designer, owner, contractor, and millworker meet to establish the quality of the finish work;
  • mockup approval of casework, paneling, or flooring to verify the desired quality level;
  • list of approved mills or suppliers that deal with urban wood near the project; and
  • clarification of the grade (or lack thereof) provided by the mill or supplier for the urban wood—NHLA grades are probably the best source for these, but there is no recognized grade for log-run material (it should be listed to give the cabinet shop an idea of what to expect).

Another important provision, especially for casework or stairs, is to use (AWI/AWMAC/WI) standards to define the expected quality standard of the completed work. These standards control the amount of grain and color-matching between members to ensure a uniform appearance is achieved (or not achieved, depending on the designer’s intent). This is especially the case when using wood such as ash that can have a broad variety of color and grain pattern within the same board.

When the designer is aware of the possibilities, a truly remarkable piece of casework or paneling can be achieved. By utilizing urban lumber, owners can attach a great story and add a unique component to any building.

From the disaster of emerald ash borer infestation emerges new opportunities to enrich urban spaces and provide new memories from city trees. Architects, contractors, and owners have the ability to use and promote this unique resource, but as with any ‘new product,’ the various parameters must be understood for its correct use to achieve the best results for all involved.

Provided design/construction professionals and urban forestry workers know the ideal criteria for board length, importance of identifying special cuts early, and the need to sort or grade material prior to delivery to fabricators to minimize waste results, urban lumber has great opportunity for richer character in the wood, making for a unique finish with a great back story.

1 This comes from Therese Poland and Deborah Therese’s April/May 2006 article in Journal of Forestry, “Emerald Ash Borer: Invasion of the Urban Forest and the Threat to North America’s Ash Resource.” (back to top)
2 See Marianne Rzepka’s August 22, 2010 article in the Ann Arbor Chronicle, “Seeds and Stems.” (back to top)
3 For more information, visit (back to top)
4 The project was profiled in Bradford McKee’s October 6, 2009 article, “Traverwood Branch Library,” which appeared in Architect. (back to top)

J. Gerard Capell, FCSI, AIA, CCS, is principal of Capell Design Associates in Milwaukee, Wisconsin, providing architectural design and specification writing services. His experience has broadly evolved from his work in California, Wisconsin, and Florence, Italy; this includes work as a rough and finish carpenter, architect, and specification writer on healthcare, education, civic, residential, senior living, retail, and industrial projects. Capell has served on CSI’s Certification Committee and Board, along with positions at the region and chapter level over his 28 years as a member. He can be reached at