Tag Archives: Energy efficiency

Reducing Environmental Impact with Coatings

Images courtesy Sto Corp.

Images courtesy Sto Corp.

by Rankin Jays, MBA

A quick review of the new 2012 International Building Code (IBC) is evidence enough the environmental lobby continues to grow. Broadly speaking, the new code requires more insulation, a tighter envelope, improved ducts, better windows, and more efficient lighting. As it becomes understood the planet cannot sustain the environmental impact associated with meeting a growing energy demand, energy conservation needs to improve.

However, the code is merely the minimum acceptable standard and it still leaves choices—especially the option to make a bigger individual contribution toward energy savings. The professional community recognizes the opportunity to influence these choices on an even larger scale. Architecture 2030—a non-profit, non-partisan, and independent organization—was established in response to the climate change crisis in 2002. According to the group:

Buildings are the major source of global demand for energy and materials that produce by-product greenhouse gases (GHG). Slowing the growth rate of GHG emissions and then reversing it is the key to addressing climate change.1

The U.S. Green Building Council (USGBC) launched Leadership in Energy and Environmental Design (LEED) in 1998 as a voluntary, market-driven program to recognize environmental stewardship and social responsibility in building design, construction, operations, and maintenance. The knock-on effect was to focus the building supply chain on the industry’s products, how they were made, efficiency, and where and how they were brought to market.

Buildings are the problem and buildings are the solution. Inadequate insulation and air leakage are leading causes of energy waste in most projects, and coatings selection can play a big role in energy saving opportunities.2

Cool roofs
According to the U.S. Department of Energy (DOE), cool roofing is the fastest growing sector of the building industry, as owners and facility managers realize the immediate and long-term benefits of roofs that stay cool in the sun.3 The Oak Ridge National Library (ORNL) have explored the energy efficiency, cost-effectiveness, and sustainability of cool roofs and have developed a calculator that computes the reduction in energy consumption by substituting a cool roof for a conventional roof. Cool roofs can create a cooler interior space in buildings without air-conditioning, making occupants more comfortable, reducing carbon emissions by lowering the need for fossil-fuel generated electricity to run air-conditioners, and potentially slowing global warming by cooling the atmosphere.4

Cooler building surface temperatures reduce energy demand.

Cooler building surface temperatures reduce energy demand.

Cool (i.e. white) flat roofs have been a requirement in California since 2005, while it has been relatively easy to get building owners to adopt this it was not without incentives such as federal tax credits for approved roofing systems.5 The cool roof requirement was extended to include sloped roofs in certain Climate Zones in 2009 as part of the California’s Title 24, Building Energy Efficiency Standards. Further, roofing systems meeting LEED’s Solar Reflectance Index (SRI) criteria could qualify for LEED-New Construction (NC) v2.2 Sustainable Sites (SS) credit 7.2, Heat Island Effect–Roof.

If you are installing a new roof or reroofing an existing building, a systems approach to providing an energy-efficient roof should be taken with a cool roof considered.

Simply put, traditional dark-colored roofing materials strongly absorb sunlight, making them warm in the sun and heating the building. White or special ‘cool color’ roofs absorb less sunlight, staying cooler in the sun and transmitting less heat into the building. This reduces the need for cooling energy if the building is air-conditioned, or lowers the inside air temperature if the building is not cooled.

Steven Chu, PhD, has been talking about the benefits of white roofs since being appointed as U.S. Secretary of Energy. In 2010, he mandated all new roofs on Energy Department buildings be either white or reflective. In a statement, he noted the cooling effect white roofs have on buildings, especially air-conditioned ones, as well as their ability to drastically lower energy costs—an estimated $735 million per year, if 85 percent of all air-conditioned buildings in the country had white roofs.

“Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,” Chu said.

White roofs can also reduce the urban heat island effect. This is a phenomenon caused by all the dark, heat-absorbing surfaces in urban areas. A study by the Lawrence Berkeley National Laboratory’s (LBNL’s) Heat Island Group6 showed increasing the reflectivity of road and roof surfaces in urban areas with populations of more than one million would reduce global carbon dioxide (CO2) emissions by 1.2 gigatons annually—the equivalent of taking 300 million cars off the road.7

IR-reflective pigment coatings
Infrared (IR) reflective pigment technology in coatings were first used more than 30 years ago, although full commercialization has only been quite recent.8 The technology and entry costs are relatively lower now than in the past, but the manufacturing process and quality control remains specialized within the scope of only a small number of manufacturers.

Combining the IR reflective pigmentation with the performance of current polymer coatings technology can produce a long-lasting coating offering significant energy-saving potential along with numerous other benefits. The higher solar reflectance increases the coating lifecycle by reducing thermal expansion and contraction of the substrate. The cooler surface temperature reduces polymer degradation within the paint film; reduced energy demand carries the obvious economic and environmental advantages. Additionally, they also make a positive contribution toward the reduction of the urban heat island effect.

The primary purpose of IR-reflective coatings is to keep objects cooler than they would be using standard pigments. These coatings can reduce the heat penetrating the building though the roof and exterior walls, lowering the load on the air-conditioning system and thereby increasing a building’s energy efficiency. An overview of the basics behind this technology is described on the Eco Evaluator website, stating:

These thermally emissive/reflective coatings offer a range of applications such as on roofs and walls of buildings. These coatings will adhere to a variety of materials such as composite roof shingles, metal roofs, and concrete tile roofs as well as stucco, plywood, and concrete block walls. When considering thermally emissive/reflective cool coatings be sure to look for metal oxide and infra-red emissive pigments. These ingredients are necessary to block ultra violet rays and reflect infrared radiation.9

Infrared (IR) reflective coatings are gaining in popularity as exterior design incorporates more vibrant and saturated colors.

Infrared (IR) reflective coatings are gaining in popularity as exterior design incorporates more vibrant and saturated colors.

In 2005, ORNL produced a lengthy study on the efficacy of IR reflective exterior wall coatings and found they can offer up to 22 percent savings on cooling energy costs when compared to a regular architectural coating of the same color. Overall effectiveness depends on the darkness of the coating color and how exposed the surfaces are to direct sunlight.

Radiant heat barriers
Passing on the whole exterior repaint is an option—a radiant heat barrier in the attic space, primarily designed to reduce summer heat gain and decrease cooling costs, can be considered. The barrier consists of a highly reflective material that ‘bounces’ radiant heat and reduces the radiant heat transfer from the underside of the roof to the other surfaces in the attic, such as air-conditioning ducts.10

Air barriers
A report from the National Institute of Standards and Technology (NIST), “Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use,” confirms continuous air barrier systems can reduce air leakage by up to 83 percent and energy consumption for heating and cooling by up to 40 percent.

In new construction where we may have been accustomed to seeing a building ‘wrap,’ air barriers are now commonly fluid-applied air and moisture barriers, providing a continuous and fully adhered membrane across the sheathing’s entire surface with obvious durability advantages gained from having a chemical and mechanical bond between the air barrier and the substrate.

Liquid technology also allows for faster, easier application of the air barrier and reduces the risk of improper installation as they are spray-, brush-, or roller-applied to the surface. The exception would be where mesh, fabric, or transition products are embedded and sealed within the fluid applied products.

As building codes continue to evolve with an emphasis on energy efficiency and sustainability, the value of air barriers is becoming much more apparent. In fact, research has proven air barriers actually play a larger role in energy efficiency than exterior continuous insulation.11


This image shows a spray application of a vapor permeable fluid applied membrane.

Niche or not?
With the exception of cool roof coatings, why have the rest of these technologies not amounted to much more than niche products? There is perhaps a large amount of skepticism following early entrants in the market that made outlandish claims of paint’s insulating qualities that were revealed as scams.

For skeptics out there, look no further than the stripes on a zebra for a lesson on reducing radiant heat. The black and white pattern on these animals can reduce the animal’s surface skin temperature by 8 C (17 F). The temperature differences over the black and white stripes result in differential air pressure, which produces minute air currents that cool the surface.

As an example of biomimicry of this natural phenomenon, the concept was commercialized by Daiwa House in Japan where the interplay of black and white on the façade reduced the summer indoor air temperature by 4.4 C (8 F).

It should be noted, cool roof and IR coatings will only have an impact where cooling costs are higher than heating costs. In higher/cooler latitudes there could be a heating cost penalty during the winter as a result of using these coatings. Following the zebra’s example they are only provided with an insulating layer of fat beneath their black stripes since the tissue below the reflective white stripes does not need it.

Coatings are in no way meant to replace insulation, but they can make an effective contribution in reducing the downstream environmental impact by reducing energy usage. With new coatings in the market, and more coming in every day, these products are contributing to energy savings and reducing energy dependency.

1 Visit www.architecture2030.org/2030_challenge/the_2030_challenge. (back to top)
2 Visit www.ornl.gov/sci/roofs+walls/insulation/ins_01.html, Department of Energy. (back to top)
3 For more on cool roofing, see “Rethinking Cool Roofing: Evaluating Effectiveness of White Roofs in Northern Climates” by Craig A. Tyler, AIA, CSI, CDT, LEED AP, in the November 2013 issue. (back to top)
4 Visit www1.eere.energy.gov/buildings/pdfs/cool_roof_fact_sheet.pdf. (back to top)
5 Visit www.energy.ca.gov/2008publications/CEC-999-2008-031/CEC-999-2008-031.pdf. (back to top)
6 For more, see Lawrence Berkley National Laboratory 2009, Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets. (back to top)
7 Visit inhabitat.com/having-white-roofs-would-save-the-u-s-735-million-per-year/. (back to top)
8 For more on IRCCs, see our web-exclusive article, “Reflecting on the Versatility of IRCCS,” by Lynn Walters at www.constructionspecifier.com. (back to top)
9 Visit www.ecoevaluator.com/building/energy-efficiency/heat-reflective-paints.html. (back to top)
10 Visit www.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/. There is a great fact sheet from Oak Ridge National Laboratory with more information on radiant heat barriers. (back to top)
11 See, NISTIR 7238, “Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use.” (back to top)

Rankin Jays is a product manager (coatings) for Sto Corp. He joined the company this year to oversee the coatings product line, introducing new products such as architectural coatings. Jays’ experience with coatings goes back nearly 30 years, starting as a paint maker while at Victoria University in New Zealand. He received his MBA from Massey University. Jays can be contacted by e-mail at rjays@stocorp.com.

Impact of Advancements in Model Energy Codes: The Value of Energy Conservation

There are several statistics, trends, and implications related to energy consumption and conservation that can be quite eye-opening.*

Economic impact

  • annual national energy bill for buildings is more than $415 billion;
  • average household spends $1900 a year on energy;
  • improving energy efficiency by 50 percent has an annual value of $950 for the average household; and
  • during the nominal 75-year lifespan of a typical home, $950 a year in energy savings has a ‘present worth’ value of $18,500.

Resource impact

  • commercial and residential buildings account for 41 percent of U.S. energy consumption—a number higher than for industry or transportation;
  • most energy consumed in buildings is produced by fossil fuels (i.e. non-renewables like coal, oil, and natural gas), which can compete with a national security interest to conserve these resources and reduce dependency on foreign sources; and
  • if all U.S. households were to apply even a modest R-3 of continuous insulation (ci) to walls, the estimated energy savings is equivalent to 70 large oil tankers per year, the total energy produced at five large nuclear power plants per year, or removing 7 million vehicles from use (which equates to 2.5 billion gallons of gasoline not consumed each year).

Environmental impacts

  • burning of fuels to produce energy releases air pollutants including sulfur dioxide, nitrogen oxides, carbon monoxide, and particulates having consequences including smog, acid rain, respiratory disease, and many other negative human health and ecological effects;
  • energy consumption or losses from buildings generate 1.2 billion tons of carbon dioxide (a greenhouse gas [GHG]) into the atmosphere; and
  • if all U.S. households were to apply the aforementioned R-3 of ci, air pollutants could be reduced by 30 million tons per year (or 2.5 percent of the total).

* This information comes from the U.S. Energy Information Administration’s (EIA’s) 2009 annual energy review, a New York State Energy Research and Development Authority (NYSERDA) report, Comparison of Current and Future Technologies,” and a 2000 Franklin Associates paper, “Plastics Energy and Greenhouse Gas Savings Using Rigid Foam Sheathing Applied to Walls of Single Family Residential Housing in the U.S. and Canada.”

To read the full article, click here.

Impact of Advancements in Model Energy Codes: What’s the effect on insulation?

Images courtesy PIMA

Images courtesy PIMA

by Jared O. Blum

In response to a national interest in, and policies for, conservation of energy, model energy codes are striving to advance the way commercial and residential building envelopes are insulated. The effect on how design professionals specify materials for thermal management will be substantial.

The International Code Council’s (ICC’s) 2012 International Energy Conservation Code (IECC) calls for a 30 percent increase in building energy savings as compared to the 2006 code. This represents the single largest efficiency increase in the history of the model energy code.

For walls, a continuous insulation (ci) system is featured as a solution in recent model energy codes because it effectively addresses these challenges. When it comes to commercial roofs, significant savings can be attained by upgrading insulation to provide an R-value meeting current code standards and practice.

Light frame and mass wall systems with continuous polyisocyanurate (polyiso) insulation for code-compliant commercial building construction.

Light frame and mass wall systems with continuous polyisocyanurate (polyiso) insulation for code-compliant commercial building construction.

Continuous insulation in walls
In American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2007, Energy Standard for Buildings Except Low-rise Residential Buildings, ci is defined as:

insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior, exterior, or is integral to any opaque surface of the building envelope.

Of course, this insulation approach is not new—it has been commonly used for many years on various types of low-slope roofing assemblies. Since 20th century construction practices were developed during periods of ample and cheap energy, its use on both residential and commercial building walls has lagged behind its energy-saving potential. This situation is changing through the emphasis of higher-performing wall assemblies in newer model energy codes. Like any construction material, continuous insulation must be properly specified to ensure its intended performance and appropriate use.

Materials: function and versatility
As shown in Figure 1, ci can be used with various wall structural systems and cladding materials such as:

  • cement board;
  • portland cement stucco;
  • wood lap;
  • brick veneer;
  • stone; and
  • vinyl siding.

In these applications, the primary function of continuous insulation is to provide code-compliant or better energy conservation performance. Additionally, properly qualified and installed ci products can serve other important functions for exterior wall assemblies, including air barriers and water-resistive barriers (WRBs). When laminated to structural materials, ci can even provide structural functions such as wall bracing. (The designer should refer to the manufacturer’s data for code-approved capabilities.)

R-value is the measure of resistance to heat flow through a given thickness of material; the higher the R-value, the greater that resistance.

R-value is the measure of resistance to heat flow through a given thickness of material; the higher the R-value, the greater that resistance.

Various code-compliant foam plastic insulating sheathings and other types of materials are available to address ci applications on walls. The most common foam plastic insulating sheathing products are manufactured and specified in accordance with ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, or ASTM C1289, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board.

Material types include polyisocyanurate (polyiso) foam, expanded polystyrene (EPS), and extruded polystyrene (XPS). Each product type has different thermal properties (which affect required thickness), costs, and capabilities (Figure 2). Model building code requirements for foam plastics are found in Chapter 26 of the International Building Code (IBC).

Modern energy and building code requirements
Continuous insulation provides one of the most thermally efficient ways of complying with modern energy codes. It mitigates avoidable heat loss due to thermal bridging in walls and roofs not continuously insulated (Figure 3). Modern energy code requirements for walls feature the use of continuous insulation as shown in Figure 4.

When using continuous insulation to meet or exceed the applicable energy code, certain matters of building code compliance should also be considered.

Many ci products can be used as a water-resistive barrier behind cladding, offering water protection and thermal performance in one product. (Design professionals should refer to manufacturer installation instructions and code-compliance data.) Alternatively, WRBs can be separately applied to walls with continuous insulation.

Continuous insulation minimizes thermal bridging and provides favorable economic and performance benefits over use of cavity insulation alone in exterior walls.

Continuous insulation minimizes thermal bridging and provides favorable economic and performance benefits over use of cavity insulation alone in exterior walls.

Wind pressure resistance
For code compliance guidance on wind pressure resistance of foam sheathing materials, one should refer to the American Chemistry Council’s (ACC’s) Foam Sheathing Committee Technical Evaluation Report (TER) 1006-01, Prescriptive Wind Pressure Performance of Foam Plastic Insulation used as Insulating Sheathing in Exterior Wall Covering Assemblies,1 along with the manufacturer’s installation instructions and design data.

It is important to verify the wind pressure resistance of other wall assembly components—including framing and siding—because testing has shown they may not be as strong as the foam sheathing material itself under wind pressure loading.

Cladding (siding) attachment
Various proprietary and standard fasteners and connection strategies can be used for attachment and support of cladding materials when installed over continuous insulation. For guidance, refer to the Foam Sheathing Committee’s Tech Matters, “Guide to Attaching Exterior Wall Coverings through Foam Sheathing to Wood or Steel Wall Framing.”

This document features solutions for direct attachment of cladding through foam sheathing and use of furring placed over and attached through foam sheathing. Both these practices minimize thermal bridging through ci due to cladding connections. Design professionals should also refer to the cladding manufacturer’s installation requirements. For example, such documentation will list minimum siding fastener size, how penetration into framing should be maintained, and whether longer fasteners are required.

For this table, wall R-values are shown as cavity insulation alone or as XX + X where the first number is the cavity insulation R-value and the second is for continuous insulation. (Continuous insulation R-values are shown in red.) The commercial Wall R-values are based on all commercial building use groups, except R (residential) which may require additional continuous insulation depending on climate zone.

For this table, wall R-values are shown as cavity insulation alone or as XX + X where the first number is the cavity insulation R-value and the second is for continuous insulation. (Continuous insulation R-values are shown in red.) The commercial Wall R-values are based on all commercial building use groups, except R (residential) which may require additional continuous insulation depending on climate zone.

Fire performance
Foam plastics are held to a comprehensive set of fire performance requirements that include various types of tests and criteria to address flame spread, smoke development, and ignition protection. By far the most significant code requirement that applies to walls with continuous insulation (foam plastics) is the National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components. This flame spread test uses full-scale, multi-story wall assemblies.2 In general, compliance with NFPA 285 is not required for buildings meeting limitations for Type V construction or one- and two-family dwelling construction.

Moisture vapor retarders
It is important to ensure ci is specified together with moisture vapor retarders in such a way that moisture vapor is properly managed. Recent building code improvements (i.e. 2009 IBC Section 1405.3, Vapor Retarders) ensure adequate R-value is provided in different climates to prevent condensation by keeping walls warm (i.e. above dewpoint) and to ensure vapor retarders are used in a manner that promotes seasonal drying capability.

Energy codes and the roof
One of the best and simplest ways to achieve a high degree of energy efficiency is by increasing the levels of insulation on the roof. In fact, for long-term energy savings, the commercial roofing market provides a significant multiplier effect to accelerate energy efficiency efforts. For every new roof installed on a building, approximately three additional ones are installed on existing buildings to replace older, less energy-efficient assemblies.

More than 370 million m2 (4 billion sf) of flat roofs are retrofit annually, with untold other existing roofs waiting for their turn.3 If all these commercial roofs were upgraded to meet the requirements of the 2012 IECC, energy savings would be significant.

Published by Polyisocyanurate Insulation Manufacturers Association (PIMA) and the Center for Environmental Innovation in Roofing, Roof and Wall Thermal Design Guide provides information regarding the prescriptive thermal value tables in the 2012 IECC and the references to these tables in the 2012 International Green Construction Code (IgCC). The guide translates this information into simple and straightforward roof and wall R-value tables covering the most common forms of commercial opaque roof and wall construction.

For example, R-values for the 2012 IgCC and IECC for “roofs with insulation entirely above deck” are determined by reducing the overall roof assembly U-factor by 10 percent, and converting the assembly U-factor to the corresponding insulation R-value. Resultant R-values in the table (Figure 5) are rounded to the nearest 0.5 R-value.

In 2013, both ICC and ASHRAE adopted language making it clear once and for all the R-value required for new building construction also applies where “the sheathing or insulation is exposed” during reroofing. For attics and other roofs, the rated R-value of insulation “is for insulation installed both inside and outside the roof or entirely inside the roof cavity.” This information can be found in Figure 6.4

R-values for roofs with insulation entirely above deck, as set out by the building codes.

R-values for roofs with insulation entirely above deck, as set out by the building codes.

R-values for insulation installed inside and outside the roof, or entirely inside the roof cavity.

R-values for insulation installed inside and outside the roof, or entirely inside the roof cavity.

Construction detailing
It is important to provide workable and complete construction details for walls and roofs with ci to ensure a constructible and functional assembly relating to many of the topics discussed in this article. Construction details to consider include:

  • envelope component attachments;
  • integration of flashing and WRB;
  • integration of furring (if used) around wall penetrations and flashing;
  • attachment of cladding to wall framing through ci or to furring;
  • details for cladding attachments through ci at inside and outside corners; and
  • installation detailing per NFPA 285 tested assembly when required. Some useful detailing resources or concepts can found from various sources. Proprietary cladding systems may also include details for accommodation of continuous insulation.

The advancement of model energy codes represents another step forward in ensuring a reduction in energy consumption, which in turn helps stabilize or even decrease utility costs.

Whether for new construction or energy-efficient retrofits, new ways of thinking about insulation are leading to improved products, refined assemblies, and better outcomes. Photo © BigStockPhoto/Gina Sanders

Whether for new construction or energy-efficient retrofits, new ways of thinking about insulation are leading to improved products, refined assemblies, and better outcomes. Photo © BigStockPhoto/Gina Sanders

1 The group’s membership includes numerous foam sheathing manufacturers, along with the ACC’s Center for the Polyurethanes Industry (CPI), EPS Molders Association (EPSMA), Extruded Polystyrene Foam Association (XPSA), and Polyisocyanurate Insulation Manufacturers Association (PIMA). For more information, visit www.foamsheathing.org. (back to top)
2 For more information, refer to the Foam Sheathing Committee’s Tech Matters, “NFPA 285 Tested Assemblies Using Foam Sheathing,” and the specified manufacturer’s fire test data. (back to top)
3 This comes from a 2012 report, “Twenty-five Years of Polyiso: The Energy and Environmental Contribution of the Polyiso Insulation Industry 1987−2011” prepared by Tegnos Research for PIMA. (back to top)
4 Additional details on these wall and roof types, as well as others, can be found in the Roof and Wall Thermal Design Guide. Visit c.ymcdn.com/sites/www.polyiso.org/resource/resmgr/latest_news/icodesguide2012_snglpgs.pdf. (back to top)

Jared O. Blum is the president of the Polyisocyanurate Insulation Manufacturers Association (PIMA), the Washington-based North American trade association representing manufacturers of polyiso foam insulation. He can be reached via e-mail at joblum@pima.org.

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Out of Sight, Not Out of Mind: Specialty Insulations for Enhanced Moisture Protection

by Ram Mayilvahanan

Neither expanded nor extruded polystyrene (EPS nor XPS) are intended to provide the primary waterproofing or dampproofing on below-grade foundation walls or under slabs. However, rigid foam insulation can offer an additional barrier to ground water, especially those products designed with that goal in mind.

Two classes of products to consider for enhanced moisture protection are faced insulation panels and panels with pre-cut drainage grooves.

Rigid foam insulation is available with polymeric laminate facers virtually impervious to moisture. The thin factory-applied facer keeps water from entering the panel, and thereby away from concrete foundations and slabs.

In instances where a building sits on a high water table or the soil is otherwise regularly saturated, rigid foam insulation drainage boards can help reduce the hydrostatic pressure of the backfill on the foundation wall. Such boards have narrow, regularly spaced channels cut into the face of the foam. A factory-applied filtration facer installed over the grooved face keeps soil out of the channels so water continues to flow. One such widely available product can drain up to 62 l/min/meter (5 gal/min/ft).

To read the full article, click here.

Out of Sight, Not Out of Mind: Specifying thermal insulation below-grade and under-slab

All photos courtesy Insulfoam

All photos courtesy Insulfoam

by Ram Mayilvahanan

In the push to forge more energy-prudent buildings, design professionals are leaving no part of the envelope unexamined. Walls and roofs have always presented a clear target for better thermal performance. Somewhat less obvious are surfaces that are out of sight—below-grade foundation walls and floor slabs. Well-engineered insulation in these locations can provide significant energy savings.

What separates below-grade insulation types from one another? Moisture retention, R-value stability, and compressive strength are the key performance attributes to consider when evaluating and comparing different below-grade insulations.

Below-grade insulation enhances thermal performance in buildings and helps protect concrete from freeze-thaw damage.

Below-grade insulation enhances thermal performance in buildings and helps protect concrete from freeze-thaw damage.

Installing thermal insulation on below-grade foundation or perimeter walls and under slabs is important because un-insulated concrete provides a thermal and moisture bridge between the heated building interior and the relatively cooler earth surrounding the building, or through exposed slab edges to the outside air.

The U.S. Department of Energy (DOE) estimates insulating the exterior edge of slabs in slab-on-grade buildings can reduce winter heating bills from 10 to 20 percent.1 Likewise, the lack of insulation on below-grade foundations, crawlspaces, and under slabs accounts for up to 25 percent of a structure’s total energy loss, the Expanded Polystyrene (EPS) Industry Alliance reports.2

In addition to saving energy, installing thermal insulation on foundations and slabs helps:

  • improve comfort in below-grade and daylight basements;
  • reduce interior condensation on foundation walls; and
  • protect concrete from freeze-thaw cycling, thereby helping minimize cracking, spalling, and frost heave.

In below-grade and under-slab applications, rigid foam insulation reigns compared to other materials. Traditionally, specifications have called for extruded polystyrene (XPS) in these areas, but EPS can perform as well, while being less costly and offering more design flexibility.

Drip, dry, drip, dry
Moisture degrades a material’s ability to insulate. Below-grade insulation frequently contacts wetted soil, so the key is to select a material that does not retain moisture. How do XPS and EPS compare with regard to moisture retention?

EPS made in accordance with ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation (which governs both EPS and XPS), has very low moisture retention—it does not waterlog.

In-situ test results for below-grade insulation/

In-situ test results for below-grade insulation.

This means EPS releases moisture rapidly, quicker than XPS does. Over time, when soil is wetted and dried as the weather varies, EPS retains a lot less moisture than does XPS. A real-world evaluation by Stork Twin City Testing—an accredited independent testing laboratory—demonstrated this point. The lab examined sheets of EPS and XPS removed from a side-by-side installation after 15 years in service on a below-grade foundation in St. Paul, Minnesota. As summarized in Figure 1, the XPS was significantly wetter on extraction, with 18.9 percent moisture content by volume compared to 4.8 percent for the EPS. Further, after 30 days of ‘drying’ (to simulate practical temperature swings), the XPS still had elevated moisture of 15.7 percent, while the EPS had dried to 0.7 percent.

In cases where higher moisture shielding of foundations and slabs is crucial, EPS insulations are available with water-impervious facers and pre-cut drainage channels. (For more information, see “Specialty Insulations for Enhanced Moisture Protection”). These facers, which are factory-laminated to both sides of the EPS, make it almost impervious to moisture, and provide an enhanced level of moisture protection performance.

R-today, gone tomorrow
Beyond helping to keep water away from other building components, the degree to which exterior-applied insulations absorb moisture affects their R-value.

The aforementioned 15-year Minnesota in-situ testing also evaluated the R-value of EPS and XPS. The results showed the former retained 94 percent of its specified R-value, whereas XPS experienced a loss of almost half its R-value.3

Rigid foam insulation can be used on either or both the exterior and interior of below-grade foundation walls.

Rigid foam insulation can be used on either or both the exterior and interior of below-grade foundation walls.

A layer of foam insulation helps protect the water proofing on foundation walls during backfill.

A layer of foam insulation helps protect the water proofing on foundation walls during backfill.









In addition to the degrading effects of moisture on R-value, the aptly called ‘thermal drift’ of an insulator is another factor affecting insulating performance. EPS has long-term stable R-values, since it uses blowing agents that by design are already completely diffused at the time of manufacturing. In comparison, XPS uses blowing agents that diffuse from the foam’s cellular structure over the product’s life, thereby reducing its thermal performance with each day in the field. Thermal stability also gives EPS its ability to retain R-value through years of freeze-thaw cycling.

A simple way to check the long-term thermal performance of any insulation is to review the manufacturer’s warranty. Established EPS manufacturers typically warrant 100 percent of the published R-value for 20 years. By comparison, most XPS warranties typically cover only up to 90 percent of the published R-value in order to account for the degradation occuring in the field.

The International Energy Conservation Code (IECC) enumerates prescriptive R-value requirements for below-grade walls and slab-on-grade floors by climate zone. In the 2012 code, Table C402.2 (“Opaque Thermal Envelope Requirements”) has specific values, but it should be confirmed with the local building official.

When is strong too strong (or too expensive)?
A good below-grade insulation must be strong enough to withstand the pressure of the loads above it. For this reason, some EPS manufacturers provide a wide range of compressive strengths, from 69 to 414 kPa (10 to 60 psi)—this has made the material suitable for use as structural fill for highways and airport runways.

The compressive resistance of EPS is demonstrated in its use as geofoam in demanding structural void fill applications.

The compressive resistance of EPS is demonstrated in its use as geofoam in demanding structural void fill applications.

While the insulation strength is an important consideration, a common erroneous design assumption often leads to over-engineering for compressive resistance, which in turn adds unnecessary, and often very high, material costs. Over-engineering a building with 689 kPa (100 psi) below-grade insulation, when a 276 kPa (40 psi) board would have been adequate, can almost double the material cost.

Avoiding this error requires taking into account how the slab and sub-grade interact. Often, the assumption is made that concentrated loads applied to a slab (such as from a forklift or a vehicle) transfer directly to the sub-grade in a pyramidal prism shape. In reality, concrete slabs distribute loads evenly, which results in a lower compression strength needed for the insulation.

For example, a typical case might involve a 100-mm (4-in.) thick concrete slab under a forklift load of 3629 kg (8000 lb) applied via a tire footprint of 0.04 m2 (60 sq. in.). If one assumes the load transfers through the slab at a 45-degree angle, the tire’s force would be distributed over approximately 0.16 m2 (250 sq. in.) of insulation, for a force of 220 kPa (32 psi).

A more accurate calculation involves using a formula for the Theory of Plates on Elastic Foundations:

W = F / 8√(KD)


  • W = slab deflection;
  • F = load on slab;
  • K = subgrade reaction modulus of insulation in lb/cu. in.;
  • D = EH3 / 12(1−u2);
  • E = modulus of elasticity of concrete in lb/sq. in.;
  • h = thickness of concrete slab; and
  • u = Poisson’s ratio for concrete (0.15).

The result of such a calculation for the previously stated scenario, and with a 50-mm (2-in.) thick layer of Type II EPS, for example, is a load on the insulation of only 17.2 kPa (2.5 psi)—well below the 58.6 kPa (8.5 psi) compression rating (at one percent deformation) of commonly available Type II EPS. Therefore, the EPS has plenty of strength for the applied load. As XPS is more expensive per inch than EPS, specification of a higher strength XPS would have unnecessarily increased the insulation costs.

Don’t be bugged
Sometimes concerns arise about rigid foam insulations used below grade providing a conduit for termites or carpenter ants to burrow through to reach the wood in a structure.

Typical below-grade installation.

Typical below-grade installation.

Following building code best practices in termite-risk regions can alleviate this concern. Local codes should be consulted for specific requirements. Additionally, some rigid foam insulations are available with non-toxic, inert additives that deter wood-damaging insects throughout the insulation’s service life.

Installing rigid foam insulation
In below-grade applications, rigid foam insulation is applied over the dampproofing or waterproofing using a polystyrene-compatible adhesive or mechanical fasteners (Figure 2). Applying a bead of polystyrene-compatible caulk or mastic to the top of the insulation board minimizes water infiltration behind it. Additionally, the waterproofing or dampproofing must be properly cured before insulation is installed.

For under-slab insulation, the rigid foam is typically installed over a gravel base, with a poly vapor diffusion retarder between the gravel and insulation. Additional insulation is applied along the slab edges, as this is a primary surface for heat loss. To avoid damage to the insulation, it is necessary to ensure removal of any jagged surfaces or irregularities in the substrate before installing the rigid foam panels.

In both applications, it is important to confirm all details with the insulation manufacturer and local authority having jurisdiction (AHJ).

Bottom line
Expanded polystyrene offers similar or better performance characteristics as extruded polystyrene across key below-grade and under-slab insulation attributes: moisture retention, R-value stability, and compressive strength. While XPS provides a higher R-value per inch of thickness, EPS matches the performance at a much lower cost, thanks to the latter having the highest R-value per dollar among rigid insulations. Additionally, because EPS can be designed in various sizes and compressive strengths, it provides a greater degree of flexibility than does XPS. These factors are making EPS the go-to product for building professionals to help design the right below-grade insulation solutions at the right cost.

EPS can offer myriad benefits when used in geofoam applications.

EPS can offer myriad benefits when used in geofoam applications.

Many building projects throughout North America have used EPS successfully on foundation walls and beneath slabs. For example, the project engineers for a 2012 expansion to the Cold Climate Housing Research Center in Fairbanks, Alaska, specified 300 mm (12 in.) of EPS under a 150-mm (6-in.) floor slab. They were able to use a thicker, yet lower-compressive resistance product than they had initially planned, which improved the thermal performance, at a lower cost than originally budgeted.

In an example of a hot-region project, the concrete contractor for the Starwood Hotel Finance Headquarters in Scottsdale, Arizona, installed 6040 m2 (65,000 sf) of faced EPS panels under the floor slab.

Whether selecting EPS or XPS insulation, to ensure appropriate performance, it is critical to check that the specific product has been manufactured per ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation.

1 See U.S. Department of Energy’s Office of Building Technology, “Slab Insulation Fact Sheet” at www.ornl.gov. (back to top)
2 See the EPS Industry Alliance’s “EPS Below Grade Series 103” Technical Bulletin at www.epsindustry.org. (back to top)
3 Ibid. (back to top)

Ram Mayilvahanan is the product marketing manager for Insulfoam, a division of Carlisle Construction Materials. He specializes in commercial building insulation. Mayilvahanan can be reached at ram.mayilvahanan@insulfoam.com.

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