Specifying Thermal Insulation
Canadian Standard Developments

by W. James Whalen, P. Eng
Construction Canada Magazine - November 2005

Ten years ago, Gerald R. Genge Building Consultants Inc. published a report that provided an extensive review of Canadian thermal standards. The Study of Thermal Insulation Standards for Residential Construction addressed the uniformity of thermal insulation standards (both in terms of content and format) and evaluated standards and test procedures against end-user needs. It also suggested parameters and evaluation criteria for measuring insulation performance.

The Genge study was submitted in March 1995 to the Canadian Coordinating Committee for Thermal Insulation Standards and Quality (CCCTISQ), a group comprising representatives from insulation manufacturers, end-users, testing bodies and consultants. One of CCCTISQ’s primary goals was to re-focus Canadian thermal insulation standards to ensure they were technically relevant, provided required information and were consistent.

This committee evolved into the Thermal Insulation Systems: Standards & Quality (TISSQ) consortium through the addition of Underwriters’ Laboratories of Canada (ULC), as the standards development organization, and a technical liaison group that includes the National Research Council of Canada (NRC) Thermal Insulation Laboratory. The consortium’s mission reflected the goals previously established by the CCCTISQ: “to improve the quality of Canadian standards for thermal insulation and to implement a more efficient system for the writing of these standards.”

Significant changes have occurred over the last 10 years in Canadian thermal insulation standards. This article identifies some of the related accomplishments and looks at possible future improvements that would identify performance parameters and evaluation criteria for foam plastic insulation within energy-efficient construction.

Current status
Beginning in 1996, Canadian thermal insulation standards were consolidated at ULC as the first step towards improving uniformity in terms of format and content. The accomplishments over the last nine years include the development of eight thermal insulation standards as noted in Table 1. The list includes numerous standards that replaced documents referenced in the 1995 National Building Code of Canada (NBC), as well as standards developed for products not previously addressed by the code.

To standardize the format and content of these new standards, ULC S 771, Template for Thermal Insulation Material Standards, was published in 2001. Similarly, CAN/ULC S 773, Standard for Thermal Insulation Terminology, was developed to provide accurate and consistent terms for the Canadian thermal insulation industry.

	To ensure an energy-efficient home, design professionals need thermal insulaltion standards to address attributes that can predict performance, such as comparable long-term thermal resistance (LTTR) values and compressive resistance and moisture properties under typical conditions.

A significant accomplishment related to the foam plastic insulation standards was the creation of a test procedure for predicting long-term thermal resistance (LTTR) for cellular plastic insulation manufactured with the intent to retain a blowing agent, other than air, for longer than 180 days.¹ CAN/ULC S 770-03, Standard Test Method for Determination of Long-term Thermal Resistance of Closed-Cell Thermal Insulating Foams, defines LTTR as the thermal resistance value measured after a five-year storage of a foam plastic insulation in a laboratory environment. This procedure provides a means for predicting the LTTR based on an accelerated laboratory test that estimates the change in the thermal resistance of an insulation material by means of slicing and scaling.

This test procedure is applicable to cellular plastics such as extruded polystyrene (XPS), sprayed polyurethane foam (SPF) and polyisocyanurate (polyiso) insulation. Although moulded expanded polystyrene (EPS) is also a closed-cell foam plastic insulation, the LTTR procedure is not applicable since the material is not manufactured with the intent to retain a blowing agent (other than air) for more than 180 days.

Problems with performance predictions
While the development of these new and revised thermal insulation standards demonstrates a step forward, the material properties specified in the standards do not provide a great deal of design assistance to designers and specifiers (with the exception of thermal resistance values). For instance, the other material properties specified in all foam plastic insulation standards are:

• compressive strength;
• flexural strength;
• dimensional stability;
• water absorption; and
• water vapour permeance.

The test methods referenced to determine these material properties are intended to provide a means of comparing different foam plastic thermal insulations. While the information is meant for use in specifications, product evaluations and quality control, it is unsuitable for predicting end-use product performance.
Given the material properties currently specified in thermal insulation standards, design professionals often must depend upon the assistance of industry experts to determine the appropriate material properties for specific end-use requirements.

Compressive strength
Compressive strength is typically specified based upon ASTM International D 1621, Standard Test Method for Compressive Properties of Rigid Cellular Plastics, or ASTM C 165, Standard Test Method for Measuring Compressive Properties of Thermal Insulations, to determine a value at yield or 10-per-cent deformation, whichever occurs first. However, when the compressive resistance characteristic of a foam plastic insulation is needed for design purposes, the design value must be based upon limitations that consider the type and duration of load application.

Flexural strength
Similarly, flexural strength values specified in foam plastic insulation standards are ‘breaking strengths.’ These values provide a relative measure when comparing similar products, but they do not provide the design professional with a value that can be used in actual product applications.

Dimensional stability
Dimensional stability values can be misinterpreted to mean dimensional changes in a material subjected to temperature ranges in its end-use application. However, the test method used to determine compliance with values in material standards exposes a relatively small specimen of the product to extreme temperatures in an oven for seven days. The dimensional stability values from this type of exposure would only be relevant to a designer when full thickness exposure to extreme temperatures is anticipated.

Water absorption and vapour permeance
Perhaps the most misused material properties in foam plastic insulation standards are the water absorption and vapour permeance properties. Water absorption values are determined using a laboratory test that submerges a test specimen beneath a head of water—a rare condition for most thermal insulation applications.

The vapour permeance values provide a rate of transmission through unit area of material induced by a vapour-pressure difference through a specific material thickness under specified conditions of temperature and humidity. As such, the values are not a material property that can be used for design requirements.

Design properties for product applications
Thermal insulation standards must continue developing to address design properties used to predict performance in a building environment. For example, foam plastic insulation standards need to offer

• comparable long-term thermal resistance values for different types of thermal insulation;
• compressive resistance properties under specified conditions related to intended use; and
• moisture properties for typical thermal insulation applications.

The development of the aforementioned LTTR procedure has been a step forward, but the test’s precision and bias must still be addressed to ensure the values used by designers reflect actual performance.

Figure 1

Figure 2

Some European thermal insulation standards have adopted values for compressive resistance characteristics that address compressive creep under specified conditions of loading and temperature. In addition, the recently developed ASTM D 6817-02, Standard Specification for Rigid Cellular Polystyrene Geofoam, includes compressive resistance values at one- and five-per-cent deformation to address applications where the product can be subject to either short- or long-term loads.

Foam plastic insulation is also commonly used as a component in energy-efficient building systems. For example, building systems such as insulating concrete forms (ICFs) and structural insulated panels (SIPs) typically combine a foam plastic insulation with other elements to provide an energy-efficient finished structure.

ICF systems typically consist of modular blocks, incorporating two moulded EPS insulation panels as the interior and exterior faces, connected by perpendicularly placed plastic or metal ties that yield the desired wall thickness. The required EPS mechanical properties relate to the short-term forming capacity of the ICF system. Since the required properties are beyond the scope of those specified in thermal insulation standards, the Canadian Construction Materials Centre (CCMC) has developed the Technical Guide for Modular Expanded-polystyrene Concrete Forms. The resource provides a means to confirm forming capacity based on an analytical approach, with testing of assembled product to confirm end-use performance.

Similarly, SIP systems typically consist of an EPS insulation core with structural oriented strand boards (OSB) laminated to the exterior faces of the insulation. Again, the required performance properties of the SIP system demand knowledge of material properties beyond the scope of those specified in thermal insulation standards. For this reason, CCMC has developed the Technical Evaluation Guide for Stressed Skin Panels (with Structural Ribs) for Walls and Roofs—a similar resource to the aforementioned ICF guide.

One property generally recognized for ICFs and SIPs is the effective thermal resistance of the in situ system. Wall and roof assemblies built with these energy-efficient systems provide a higher effective thermal resistance (i.e. R-value) than other construction methods.

It is important to distinguish between a wall or roof assembly’s ‘effective’ R-value—calculated using the methods detailed in the 1997 Model National Energy Code for Buildings (MNECB) and the 1997 Model National Energy Code for Houses (MNECH)—and its ‘nominal’ R-value. Thermal insulation requirements in provincial building codes are nominal values based upon the centre-of-cavity thermal resistance at a point in the wall or roof cross-section containing the most insulation. In wood frame construction, the nominal R-value of a building assembly typically indicates the amount of thermal insulation required between the framing members. The effective R-value of a building assembly, on the other hand, is the resistance of the complete assembly, including the effect of any thermal bridges in the assembly, such as wood framing members (Figure 1).

Building systems such as insulating concrete forms (ICFs) and structual insulated panels (SIPs) typically combine a foam plastic insulation with other elements to provide an energy-efficient finished structure.

Table 2 - A Guide to EnerGuide for Houses

Air leakage and moisture considerations
Unintentional air leakage can be also one of the biggest sources of heat loss in many buildings—its related test procedures are often used to determine the energy efficiency of new building construction. A building’s air leakage rate is quantified in terms of one-volume air changes per hour (acph). ICF and SIP building systems have been shown to provide much more airtight construction than other traditional materials—this performance characteristic could not be predicted using material properties currently specified in thermal insulation standards.

With ICFs, concrete is poured between two layers of expanded polystyrene (EPS), creating basement walls ready for gypsum wallboard and with a higher effective R-value than conventional finished walls without the need for a vapour retarder, studs and batt insulation.

A July 2002 report published by the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) provides moisture properties for a full range of materials typically used as building insulation.² The equilibrium moisture content (EMC) of foam plastic insulation is of interest when its wetting and drying characteristics are to be considered as a component within a wall assembly (Figure 2).

A product’s EMC is based upon the fact molecules of water are constantly leaving and returning to the material’s surface. When the same number of water molecules return to or leave the surface of a material (and said material thus neither gains nor loses water), then an equilibrium condition exists. If a material tending to high EMC is exposed to variable temperature and relative humidity (RH), it can take up water, only to give it off later—this cycle can be repeated many times. For instance, the mass fraction of water in wood can be 30 per cent or more, depending on the wood’s freshness and the atmosphere in which it is kept. The mass fraction of water in wood that has reached equilibrium at 20 C (68 F)/55 per cent RH is only 10 per cent. If this wood were brought into an environment with 40 C (104 F)/90 per cent RH, it would take up moisture from the air until its water content was 19 per cent.

The mass fraction of water in EPS plastic insulation at equilibrium is less than one per cent. After the moisture content of EPS insulation has attained its equilibrium value under given conditions, changes may take place as conditions alter, but these would not exceed 0.15 per cent of the material’s mass. In other words, EPS insulation cannot affect the internal climate of a closed-wall system as is the case with cellulosic materials, which release moisture content when exposed to a drier atmosphere and gain it from a more humid one. In this respect, EPS insulation can be said to be passive.

	Adding comfort to a home often starts from below the ground up: when used for basements, ICFs cost-effectively help families enjoy more usable living space that is warm in winter, cool in summer and energy-efficient year round.

Sustainability, software and rating programs
Builders and owners continue to move toward greater emphasis on energy efficiency and environmental awareness, as demonstrated by the popularity of concepts such as the Built Green™ Alberta framework for residential applications. These types of programs typically use hygrothermal modeling to predict the performance of the building envelope over time.

Natural Resources Canada (NRCan’s) EnerGuide for Houses program is a framework for gauging the energy efficiency of residential construction; it is intended as an objective, standardized tool. A home’s energy efficiency level is rated on a percentage scale of 0 to 100. A rating of 0 represents a home with major air leakage, no insulation and extremely high energy consumption, while a rating of 100 represents an airtight, well-insulated, sufficiently ventilated house that requires no purchased energy. (Table 2)

The energy efficiency of a proposed residential construction can be initially predicted based upon modeling using HOT 2000™, a computer model employed to predict heating and cooling costs. This program depends upon accurate information on thermal resistance values for building components.

Similarly, the Leadership in Energy and Environmental Design® (LEED®) rating system for commercial buildings provides a recognized standard for the construction industry to assess the sustainability of designs. Originally developed by the U.S. Green Building Council (USGBC), LEED has since been adapted to specific concerns and requirements of this country by the Canada Green Building Council (CaGBC).

Under LEED, points are earned for building attributes considered environmentally beneficial (e.g. energy efficiency and durability). Energy efficiency must meet requirements established under the Commercial Buildings Incentive Program (CBIP), a program established by NRCan to encourage design of energy-efficient commercial buildings. While the program uses EE4 software to assess the energy performance of building design, buildings and their systems are extremely complex.³ As such, simulators can achieve different results on the same building due to assumptions made about the performance of its components.

Additionally, one adaptation of the Canadian version of LEED has been the inclusion of a point based upon demonstration of durability of a building design.⁴ A key measure of durability could be an assessment of the moisture performance of the components used in building design. WUFI-ORNL/IBP is a menu-driven PC program that allows realistic calculation of the transient coupled one-dimensional heat and moisture transport in multi-layered building components exposed to natural weather.⁵ It is based on material properties related to vapour diffusion and liquid transport in building materials.

Canadian thermal insulation standards must develop further to address the needs of building designers. As well, the development of additional knowledge on design properties will allow insulation manufacturers to continue developing products meeting the demands of construction projects focused on energy-efficiency and sustainability.

Notes
1. This refers to ULC S 701, Standard for Thermal Insulation, Polystyrene, Boards and Pipe Covering, ULC S 704, Standard for Thermal Insulation, Polyurethane and Polyisocyanurate Boards, Faced, and ULC S 705.1, Standard for Thermal Insulation—Spray-applied Rigid Polyurethane Foam, Medium Density: Material Specification.
2. See A Thermal and Moisture Transport Property Database for Common Building and Insulating Materials: Final Report from ASHRAE Research Project 1018-RP.
3. For more on the commercial energy analysis software, visit buildingsgroup.nrcan.gc.ca/ee4.
4. For more information, see “LEED and Durability: How sustainable is CaGBC’s new credit?” by Douglas Webber, P.Eng., LEED AP, and Aaron Skeates, B.Eng. (Construction Canada, May 2005).
5. Visit www.ornl.gov/sci/btc/apps/moisture.

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 Centre (CCMC) on developing technical evaluation guidelines for structural insulated panels (SIPs) and insulating concrete forms (ICFs). He can be contacted via e-mail at jwhalen@plastifab.com.

Reprinted with permission of Construction Specifications Canada, 120 Carlton St., Suite 312, Toronto, ON M5A 4K2, from Construction Canada.