Tag Archives: B3010.50–Low-slope Roofi ng

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.

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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.

Conclusion
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 ronutzler@live.com.

Minimizing Risks with Solar Roofs

Photo courtesy GAF and Protech Roofing Service

Photo courtesy GAF and Protech Roofing Service

by Michael Russo

Commercial rooftops are an attractive platform for the installation of solar photovoltaic (PV) electricity-producing systems. These low-slope roofs offer an economical and sustainable structural foundation for renewable solar energy.1

For example, one of the largest roof-mounted PV systems in North Carolina has been online for several months at the Old Dominion Freight Line vault logistics facility in Thomasville. Approximately 7700 solar panels completely cover the warehouse’s 14,864-m2 (160,000-sf) roof and produce 1.8 megawatts (MW)—enough power to offset more than 90 percent of the building’s annual energy costs, according to Jayna Long, manager of sustainability at Old Dominion.

The roof on Old Dominion Freight Line’s vault logistics facility in Thomasville, North Carolina, features nearly 7700 solar panels. The panels produce enough power (i.e. 1.8 megawatts) to offset more than 90 percent of the building’s annual energy costs. Photo courtesy Old Dominion Freight Line Inc.

The roof on Old Dominion Freight Line’s vault logistics facility in Thomasville, North Carolina, features nearly 7700 solar panels. The panels produce enough power (i.e. 1.8 megawatts) to offset more than 90 percent of the building’s annual energy costs. Photo courtesy Old Dominion Freight Line Inc.

Success stories like Old Dominions are becoming increasingly common nationwide. However, it is important to remember a roof’s function is, first and foremost, to protect the building’s contents and occupants from the elements. In this regard, design professionals need to anticipate the potential risks associated with the installation of a roof-mounted PV system. This sort of due diligence is particularly important when installing these arrays on existing warranted roofs.

To help in these industry efforts, members of the Single Ply Roofing Industry (SPRI)—the trade association representing sheet membrane and component suppliers to the commercial roofing industry—have developed ‘PV-ready’ roof assemblies and guidelines designed to provide maximum protection for the roof as well as maintain its warranty coverage.2 

Ask the right questions
The installation of a PV system on an existing warranted roof raises many important questions for the roofing professional and building owner. For example, will the roof accommodate the added weight of the PV array? Logistically speaking, before owners decide on a solar-power system, they need to determine whether their roofs are sturdy enough to support the additional loads of the solar array.

An average solar panel and support system typically adds a minimum of 14.6 to 19.5 kg/m2 (3 to 4 lb/sf) to the existing roof. It is the design professional’s responsibility to ensure this additional weight does not exceed the load limits determined by the building’s designer.

From an economic (i.e. lifecycle cost) point of view, it makes sense the existing roof membrane’s service life will come close to matching the projected service life of the PV system. If not, a complex and costly reroofing project may be required long before the solar panels need replacement. Generally, the underlying roofing system must provide the same minimum investment horizon—generally at least 25 years—to realize the full potential of the rooftop PV system.

In La Jolla, Calfornia, the National Oceanic and Atmospheric Administration’s (NOAA’s) laboratory replacement project included 826 stand-up solar panels that complicated the roofi ng process immensely. Photo courtesy GAF and The Aerial Image

In La Jolla, Calfornia, the National Oceanic and Atmospheric Administration’s (NOAA’s) laboratory replacement project included 826 stand-up solar panels that  complicated the roofi ng process immensely. Photo courtesy GAF and The Aerial Image

Most PV arrays require penetrating the roof membrane. Even non-rack-type systems can include electrical conduits and wiring that may need to be flashed in a professional manner. It is essential the responsibility for this flashing work rests with the designer or roofing contractor and not the electrical or PV contractor.

It is also important to ensure the positive drainage designed into the existing roof system is not compromised. Using a tapered insulation system or the relocation/addition of new roof drains are two possible solutions, but they both tend to be cost-prohibitive for the property owner. Additionally, an existing drain partially covered by a solar array will make it difficult to clean out.

Roof system wind and fire code approvals have always been active topics within SPRI and the roofing industry at large. The increasing popularity of PV and vegetative roofs add another layer of complexity when attempting to meet codes and standards. In 2010, American National Standards Institute (ANSI) approved the first of three standards for vegetative roofs—ANSI/SPRI VF-1, External Fire Design Standard for Vegetative Roofs—which will also be included in the 2015 edition of the International Building Code (IBC). Further, a second SPRI vegetative roof standard was approved by ANSI in 2010—ANSI/SPRI RP-14-2010, Wind Design Standard for Vegetative Roofing Systems, which provides design guidelines associated with wind uplift and stone ballast scour.

It is likely the roofing industry will also need to investigate and standardize wind and fire code designs for rooftop PV systems. In the meantime, roofing professionals must use care when installing a PV array over an existing roof carrying FM Global (FM) Class 1 or Underwriters Laboratories (UL) Class A wind and/or fire requirements. This would also include any insurer or code body that specifies these two standards. In new construction applications, code compliance is the responsibility of the designer of record. When installing a PV array on an existing roof, specifiers should consult the roof system manufacturer to ensure existing codes are met.

Existing roof system manufacturer guarantees are an equally important topic. On older roofing systems, there may be various manufacturers represented. Even with the popularity of today’s single-source system guarantees, these documents must be evaluated in detail with the appropriate approvals given by the issuer of the guarantee.

An average solar panel and support system typically adds a minimum of 14.6 to 19.5 kg/m2 (3 to 4 lb/sf) to the existing roof. Photo courtesy GAF

An average solar panel and support system typically adds a minimum of 14.6 to 19.5 kg/m2 (3 to 4 lb/sf) to the existing roof. Photo courtesy GAF

Roof system durability
Roof durability directly affects the sustainability of any roof system; it has become a major factor in the choice of the entire assembly. At the same time, the potential benefits of the rooftop PV system itself offer long-term energy independence and environmental sustainability. Since the unique challenges of matching PV systems to compatible roofing systems are so important, the building owner needs assurance the combined rooftop PV system is designed, installed, and maintained for optimal economic and environmental benefit.

With the installation of rooftop PV, the roofing system becomes more than just a roof—it becomes a permanent platform for the continuous operation, service, and maintenance of the PV system. That is why the roofing system should be designed to minimize the need for major repairs or replacement that could compromise the continuous operation of the rooftop PV.

Many commercial PV roofing installations are financed using long-term Power Purchase Agreements (PPAs). These financial arrangements are made between a third-party that owns, operates, and maintains the PV system and a host who agrees to place the system on his or her property and purchase the system’s electric output for a predetermined period. Obviously, the continuous, undisrupted generation of solar power is critical to the fulfillment of the PPA terms. As a consequence, the margin of safety required in the design, installation, and maintenance of the roof may likely exceed normal expectations and minimum standards for commercial assemblies. In this case, the minimum standards would include roofing systems guaranteed for at least 20 years.

Raised-panel and membrane-integrated PV systems often cover most of the roof surface, and both systems require regular inspections and maintenance. Fortunately, today’s PV racks can be changed out fairly easily, which can be quite advantageous. Indeed, the frequent need for solar roof inspections and maintenance means the amount of foot traffic on these systems may be far greater than the traffic generated by an occasional piece of HVAC equipment on the roof.

Today’s raised panel PV racks can be changed out fairly easily, which can be a big advantage when performing regular roof maintenance.

Today’s raised panel PV racks can be changed out fairly easily, which can be a big advantage when performing regular roof maintenance.

Therefore, the chance of sharp tools dropping onto the roof surface or impact damage from heavy traffic or equipment installation is increased. This is why enhancing the puncture resistance of membranes used with rooftop PV systems can be so important. Solutions may include protective coverboards when practical, or other options for existing roofs, such as roof walkway pads.

In fact, some roof system manufacturers require:

  • an approved insulation board with a minimum thickness and compressive strength;
  • the addition of an approved coverboard to enhance insulation protection; and/or
  • an approved protection/separation sheet installed between the PV components and the membrane.

Protection pads should be large enough and properly secured so they do not move during the roof membrane’s expansion and contraction.

Membrane types and thicknesses
A broad selection of roofing membranes and thicknesses are available for consideration when a PV installation is planned. Options include:

  • ethylene propylene diene monomer (EPDM), polyvinyl chloride (PVC), thermoplastic polyolefin (TPO), ketone ethylene ester (KEE), and smooth and fleece-back membranes;
  • atactic polypropylene (APP) and styrene-butadiene-styrene (SBS) modified-bitumen (mod-bit) membranes; and
  • certain types of ‘enhanced’ membranes engineered for use with PV—these may include special formulations designed to accommodate the additional heat generated by the PV array or other sources.

In approving the installation of a PV system upon an existing warranted roof and maintaining the warranty, membrane manufacturers may have PV system-specific requirements the existing roof must meet, such as:

  • limitations on the current age of the existing roof;
  • restrictions on the method of roof system attachment to the structural deck;
  • restrictions for a minimum approved roof membrane thickness;
  • pre- and post-solar system installation roof inspections; and
  • a requirement the building owner make any needed repairs at his or her expense.

It is generally best to contact the roofing manufacturer for help in deciding on the membrane, thickness, and/or existing roof requirements.

Paperwork and project documentation
Roofing manufacturers frequently require project documentation forms be completed before installing a PV system over an existing warranted roof to maintain warranty coverage. For example:

  • standard pre-installation notice with roof drawings;
  • PV post warranty alteration form;
  • completed inspection reports (before and after PV installation); and
  • overburden (O/B) waiver form completed by the building owner, wherein the owner describes the PV materials to be installed (i.e. the overburden), agrees to pay for their removal when necessary, and accepts responsibility to pay for repairs caused by the overburden removal and replacement.

There are various other general terms, conditions, and suggestions that should be considered when installing PV systems on existing roofs. For example, racks should have enough clearance above the membrane to allow for roof servicing and maintenance. Additionally, PV arrays should be set so all field seams and penetrations are accessible for repair, and areas should be staged for PV materials and installation.

In new construction applications, code compliance is the responsibility of the designer of record. When installing a PV array on an existing roof, specifiers should consult the roof system manufacturer to ensure existing codes are met.

In new construction applications, code compliance is the responsibility of the designer of record. When installing a PV array on an existing roof, specifiers should consult the roof system manufacturer to ensure existing codes are met.

Many roofing system manufacturers offer certain services to design professionals and building owners in addition to the sale of roofing system products. These can include:

  • solar products;
  • financial analyses to show return-on-investment (ROI) payback period for a planned solar installation;
  • specifications and details for the roofing and solar system installations;
  • solar roof layouts;
  • a single-source warranty for the roof system and the solar integration; and
  • warranty insurance that pays for the cost of overburden removal, if needed.

Conclusion
The unique challenges of matching PV solar arrays to compatible roofing systems are so important, the specifier must ensure the combined rooftop PV system is designed, installed, and maintained for optimal economic and environmental benefit.

There is no question partnering with a roof system manufacturer offering PV-ready roofing systems can be a benefit to specifiers. In the case of SPRI, it is important to remember, each member may have its own PV-ready program and no SPRI member may necessarily have all the previously mentioned program elements. The manufacturer of the roof system specified for the project should always be consulted before the installation of a PV system on a warranted roof.

Notes
1 An earlier version of this article appeared in the November/December 2013 digital edition of Carolinas Roofing, now called Roofing. (back to top)
2 For further information, see SPRI’s Technical Bulletin 1-13A, “Summary of SPRI Membrane Manufacturer Photovoltaic (PV) Ready Roof Systems and Services” at www.spri.org. The bulletin contains general guidelines from SPRI related to ‘PV-ready’ roof assemblies. (back to top)

Michael Russo is the former editor of Roofing/Siding/Insulation and has reported on the roofing industry for more than 30 years. He is a regular contributor to Roofing Contractor, Western Roofing, Professional Roofing, Multi-housing News, and various other construction-related publications. Russo can be reached at mrusso1983@zoominternet.net.