Energy Efficient Building Systems Using EPS Insulation
by W. James Whalen, P. Eng
Construction Canada Magazine - July 2004, Vol. 46, No. 4
Molded expanded polystyrene (EPS) insulation has been used in building construction projects for over 50 years. Two energy-efficient systems relying on EPS are insulating concrete forms (ICFs) and structural insulated panels (SIPs). Both are recognized as innovative product solutions used to construct building envelopes, and are gaining wide acceptance by leaders in sustainable design.
Natural Resources Canada's (NRCan's) Office of Energy Efficiency (OEE) discusses advanced wall systems such as ICFs and SIPs on their website.1 Both systems are recognized as capable of improving the energy performance of structures and conserving natural resources
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A wall constructed using an ICF system provides a monolithic insulation layer without relying on wood studs (which result in thermal bridges).2 For calculating thermal resistance-for comparisons with the prescriptive requirements of Canada's model national energy codes-one need not take into account the anchors, ties, associated fasteners and other minor structural members completely penetrating the building envelope, provided the insulation is installed tight against the penetration's outline.
SIP systems are a type of panelized construction involving pre-fabricated wall sections. They use an advanced wood framing system whereby the members are typically spaced 1220-mm (48-in.) o.c., in comparison with 406-mm to 610-mm (16-in. to 24-in.) o.c. for wood-frame walls. A SIP wall system saves wood and significantly reduces the number of thermal bridges through a wall.
EPS insulation offers numerous advantages for buildings and their occupants. For example, the material's closed-cell structure provides excellent resistance to moisture absorption. A study performed by the Energy Materials Testing Lab (EMTL), which exposed the insulation to simulated extreme winter conditions, demonstrates EPS does not absorb appreciable moisture when installed in well-constructed roofs (see CC January 2004, "The Benefits of EPS Roof Insulation"). The study also finds EPS picks up only a small amount of moisture-in the order of 0.2 per cent by weight-even under conditions characteristic of prolonged, cold, damp winters.
In comparison to other common building materials, EPS insulation also has moderate vapor permeability-a characteristic varying with thickness (See Table 1, note 2). However, where water vapor permeance is a design issue, the insulation manufacturer should always be consulted for additional information.
Stable thermal-resistance value
EPS is non-toxic and inert, and free of CFCs (chlorofluorocarbons), HCFCs (hydro chlorofluorocarbons) and formaldehyde. Its closed-cell structure contains no captive blowing agent, so the material's thermal resistance (or R-value) remains constant. In this respect, an important distinction can be made between EPS and other rigid foam plastic insulation products where thermal resistance values decrease with the blowing agent's dissipation (i.e. thermal drift).
As other foam plastic insulation manufacturers adopt requirements for eliminating the HCFC blowing agent, they must also adjust their raw materials and manufacturing processes. The raw materials used in the EPS insulation manufacturing process, on the other hand, have remained consistent over its 50-year-plus history with constant improvements in the manufacturing process, including vacuum-mould technology. This technology involves a vacuum during the molding process, resulting in an approximate 50-per cent reduction in steam needed for the block molding process, and the homogenous fusing of the foam throughout the finished EPS block.
The National Research Council (NRC) of Canada used EPS as a reference material in developing a test procedure for predicting long-term thermal performance of cellular plastic insulation retaining a blowing agent (other than air) for over 180 days.4 In a supplementary NRC study, the thermal performance of EPS insulation remained constant over a two-year period in field conditions simulating a roofing application.
ICF and SIP system performance
EPS is used as below-grade foundation and floor insulation, exterior insulating sheathing board and roof insulation in various residential/commercial/industrial assemblies. It is also commonly used as the insulation component in exterior insulation finish systems (EIFS). In many cases, using the material as a component in energy-efficient building systems is an effective method of harnessing its proven performance properties. This is especially true in its use as the insulation component in ICF and SIP systems.
ICF systems exploit EPS insulation's strength and constant thermal performance in the construction of reinforced concrete walls providing a quiet, secure and energy-efficient building envelope. The energy efficiency results from a solid concrete wall construction clad uniformly with EPS insulation over interior/exterior wall surfaces. ICF walls have significantly lower air leakage and higher effective R-values than other construction methods.
Various ICF systems are on the market, but the ones gaining widest acceptance are modular, interlocking forming systems comprising two EPS insulation panels connected with molded plastic or metal web connectors. The space created between the panels is filled with concrete on-site, which results in an insulated, monolithic, uniformly thick concrete wall.
The effective R-value for walls constructed with ICF systems varies based on the thickness of EPS insulation layers on the interior/exterior faces of the ICF block (typical values, however, range between R-22 to R-24). The term 'thermal mass' is used to describe a material's ability to store significant amounts of thermal energy and delay heat transfer through a building component. The ideal climate for taking advantage of thermal mass has large daily temperature fluctuations. Additional information on thermal mass effect as it relates to ICF systems in various geographical locations is available from various sources, including the Portland Cement Association (PCA).
For their part, SIPs consist of oriented strand board (OSB) structurally laminated to an EPS insulation core. These systems are designed for long-term performance with specific attention paid to panel-joining methods to ensure airtight construction, strength and security. SIP system manufacturers have developed structural design charts for wind, snow and seismic load resistance capacity meeting the reliability targets of Canadian Standards Association (CSA) O 86-01, Engineering Design in Wood, using limit states design (LSD) methods.
SIPs are available in various thicknesses for wall and roof assemblies. Table One provides effective R-values for typical assemblies, including framing members at 1220-mm (48-in.) o.c.
Insulation properties
The EPS insulation used in ICF and SIP systems meets the Canadian national standard, Underwriters Laboratories Canada (CAN/ULC) S 701-01, Thermal Insulation, Polystyrene, Boards and Pipe Covering. Table Two provides material properties for the two EPS insulation types typically used in SIP and ICF systems. The former typically specifies product meeting Type 1, whereas the latter usually relies on Type 2.
Over the long term, an ICF system is a key component in energy-efficient walls. Its short-term, primary role, however, is its function as a concrete forming system, where EPS' mechanical properties provide the required capacity. (It must resist the initial hydrostatic pressure exerted during concrete placing/vibration.)
Thermal resistance is a key material property for SIP performance. However, since OSB skins are structurally laminated to the EPS insulation core material, the systems have access to additional inherent properties unspecified within CAN/ULC S 701, such as tensile and shear strengths, and modulus of elasticity. This provides SIPs with the required strength for resisting long-term structural loads.
Effective thermal resistance
Wall/roof assemblies built with ICF or SIP systems provide a higher effective thermal resistance than other construction methods, such as wood-frame construction that typically includes framing members at 406-mm or 600-mm (16-in. or 24-in.) o.c. It is important to distinguish between the 'effective' R-value of a wall/roof assembly calculated using methods detailed in the 1997 MNEC versus 'nominal' R-values.
Minimum thermal insulation requirements in provincial building codes are nominal values based on the center-of-cavity R-value at a point in the wall/roof cross-section containing the most insulation. In wood-frame construction, this nominal value typically indicates the thermal insulation required between framing members. A building assembly's 'effective' R-value, on the other hand, refers to the complete assembly, including the effect of thermal bridges, such as wood framing members.
ICF walls have a monolithic layer of insulation over the interior/exterior faces of the assembly. Therefore, the effective R-value for an above- or below-grade wall assembly built with an ICF system is greater than the effective value for a wall built using wood-frame construction methods-no framing members act as thermal bridges (Figure 1).
SIP systems use fewer framing members than conventional wood-framed wall/roof assemblies. Framing members for SIP systems are spaced at 1220-mm (48-in.) o.c. rather than the 406 mm (16 in.) typical of wood-frame construction. As such, the effective R-value for above-grade SIP wall/roof assemblies is significantly greater than for typical wood-frame construction methods (Figure 2).
According to a 2001 NRCan report, space heating and cooling accounts for 52 per cent of total energy consumption for commercial/institutional buildings, and 60 per cent for residential buildings7. ICF and SIP construction's higher effective R-values significantly reduce heat transfer compared to other construction methods resulting in lower energy consumption for heating/cooling.
Staying airtight
Air leakage test procedures are often used to determine the energy efficiency of new building construction, as unintentional air escape can be one of the biggest sources of heat loss. The air leakage rate is quantified in terms of air (volume) changes per hour (acph), and is commonly assessed via a blower door test. A review of national trends in air leakage for Canadian houses found rates vary widely for different construction methods, as illustrated in the accompanying chart (Figure 3).8 These trends reflect air leakage characteristics for housing built using wood-frame construction.
A Cement Association of Canada (CAC) case study reviewed air tightness for a 362-m2 (3900-sf) bungalow, constructed using an ICF system for above/below-grade walls in comparison to energy-efficient design requirements.9 The air leakage rate was found to be 0.22 acph, indicating a very airtight structure, and confirming significant reduction air leakage offered by ICF construction in comparison with other wall construction types.
Similarly, SIP's closed-cavity design results in significant air leakage reduction. A Northwest Territories Housing Corp. (NWTHC) demonstration house, constructed using a SIP system, achieved an air leakage test result of 0.49 acph.10
An ICF or SIP structure's air tightness also depends on other building components to maintain an energy-efficient design. Due to these types of structures' low air leakage characteristics, it is critical to design building ventilation systems that maintain indoor air quality (IAQ) and humidity control.
Code compliance for methods not in the code
ICF and SIP product development is supported by extensive research and testing to ensure long-term performance. However, these building systems are not currently described specifically in Canadian national/provincial building codes. Alternative construction methods not mentioned in the codes are permitted when their suitability can be proven. One method of demonstrating this equivalent performance is through technical evaluations.
The Canadian Construction Materials Center (CCMC) is a part of the National Research Council's (NRC's) Institute for Research in Construction (IRC). It provides a national evaluation service for innovative materials, products, systems and services supported by provincial/territorial building regulatory bodies. CCMC has developed technical evaluation guides that provide criteria for establishing ICF/SIP equivalent performance to methods described in code requirements. Based on these guides, CCMC evaluates specific products to develop evaluation reports.
Current evaluation reports for ICF systems are found on the CCMC website11 under Master Format (MF) Section 03131, Technical Guide for Modular, Expanded-Polystyrene Concrete Forms. CCMC evaluates the function of the ICF system primarily for forming capacity to establish equivalent performance with respect to National Building Code (NBC) requirements in Part 4 ("Structural Design") and Part 9("Housing and Small Buildings"). Additionally, CCMC reviews design requirements for the monolithic, reinforced concrete walls cast in the ICF system.
ICF manufacturers may use engineering design tools, such as finite element analysis simulation and optimization methods, to develop required component properties for the EPS insulation and connector ties. The next step in the product development process is to perform finished product testing to ensure adequate strength during concrete placing operations. In addition to the manufacturer's product development testing, CCMC requires a forming capacity test by an accredited testing laboratory.
For SIP systems, current evaluation reports are found on the CCMC web site under MF Section 07432, Technical Evaluation Guide for Stressed Skin Panels (with Structural Ribs) for Walls and Roofs. Equivalent performance for SIP systems in comparison to stick-frame construction methods is established with respect to NBC Part 4 ("Structural Loads & Procedures and Design Requirements for Structural Materials") and Part 9 ("Wood-Frame Construction and Heat Transfer, Air Leakage & Condensation Control").
CCMC evaluation of SIP structural design requirements ensures equivalent performance in comparison to wood-frame alternatives. (Extensive testing is required to ensure structural performance when subjected to typical load conditions.) Testing also assesses the durability of the adhesive bond between the laminated skins and the EPS insulation core material, and identifies key components providing condensation/air leakage control.
Other benefits
Construction using ICF and SIP systems is also advantageous for trades installing other parts of the wall assembly. The systems are modular, so connection surfaces are located at standard spacing, which simplifies the installation of surface finishes, such as gypsum wallboard, stucco and siding. ICF/SIP air tightness also offers noise abatement; in particular, the ICF concrete walls' mass provides additional reduction in sound transmission.
Using prefabricated systems reduces the number of subcontractors and installation steps, as they are manufactured to precise design specifications and can result in significant savings in construction time on-site, extending the building season. There are also benefits in terms of durability and structural integrity; as engineered building solutions, both systems are designed to provide excellent resistance to extreme loads caused by high winds, snow loads and seismic events (where applicable).
When ICFs are used to construct foundation walls, their monolithic insulation layer protects concrete from temperature extremes. They also reduce job-site labor costs, as the forms do not need to be removed (as is the case with other wood/metal forms used in cast-in-place concrete) and carpentry crews can be trained in the system quite easily. Ultimately, the installation cost differential can be quite small-where finished basements are desired, the disparity is even lower as ICF walls are ready for interior finishing.
Closing remarks
Architects/engineers (A/Es) must select the building system with the best combination of the desired properties based on empirical test data and knowledge of past performance. EPS insulation offers versatility in meeting various application requirements, and both ICF and SIP systems are a viable alternative for constructing wall/roof assemblies for buildings designed to achieve energy-efficiency objectives.
Notes
1. Visit http://oee.nrcan.gc.ca/r-2000/english/public.
2. Article 3.2.1.2. of the Model National Energy Codes (MNEC) for Canada addresses continuity of insulation.
3. Tye, R.P. and C.F. Baker. Development of Experimental Data on Expanded Polystyrene Roofing Insulation Under Simulated Winter Exposure Conditions. The Energy Materials Testing Laboratory, 1984.
4. CAN/ULC-S770-03, Standard Test Method for Determination of Long-Term Thermal Resistance of Closed-Cell Thermal Insulating Foams, published by Underwriters' Laboratories of Canada.
5. Bomberg, Mark and Mavinkal Kumaran. Procedures to Predict Long-Term Thermal Performance of Boardstock Foam Insulations. National Research of Canada, 1995.
6. Thermal Mass Performance of Wall Systems (CD-026.), available from the Portland Cement Association, June 2001.
7. Improving Energy Performance in Canada: A Report to parliament under the Energy Efficiency Act 1997-99. Natural Resources Canada, 2000.
8. Improving Energy Performance in Canada: A Report to parliament under the Energy Efficiency Act 2000-01. Natural Resources Canada, 2002.
9. Kensington Showcase Home Report. Cement Association of Canada, 2001.
10. "Building with Structural Panels." About Your House: North Series 1. Canada Mortgage and Housing Corp., 2001.
11. CCMC listing of evaluation reports are available online at www.nrc.ca/ccmc.
W. James Whalen, P.Eng., is the technical marketing manager at Plasti-Fab Ltd. in Calgary. He is a member of Construction Specifications Canada (CSC) and has worked extensively with the Canadian Construction Materials Center (CCMC) on developing technical evaluation guidelines for structural insulated panels (SIP) and insulating concrete forms (ICF). Whalen is a member of various ASTM International and International Standards Organization (ISO) committees, and is also part of the Underwriters Laboratories Canada (ULC) Thermal Insulation Standards Steering Committee, which is responsible for the review/approval of all national standards related to thermal insulation. He can be reached at (403) 569-4312 or jwhalen@plastifab.com.
Reprinted with permission of Construction Specifications Canada, 120 Carlton St., Suite 312, Toronto, ON M5A 4K2, from Construction Canada.
