January 5, 2017
By Amanda Sinnige and Kevin Day, LEED AP
Energy efficiency, green construction, increased insulation, net-zero—all these terms imply the same expectation: to improve the performance of buildings and minimize their impact on the environment by reducing greenhouse gas (GHG) emissions, conserving natural resources, and maximizing the service life of all building systems—all while maintaining comfortable and functional buildings. This is a tall order, but in an age where our impact on the environment can be measured by the legacy left for future generations, design/construction professionals have a responsibility to ensure every building constructed minimizes its ecological footprint. In other words, net-zero buildings are not ‘nice to have’ but an urgent necessity.
To understand how to meet the requirements of energy efficiency codes, it is helpful to review the history of energy code development for buildings in Canada, and to examine the concept of thermal bridging. It is also important to be mindful of the requirements of individual locales, since these vary by the provincial code adoption cycle. Ultimately, all these factors show how exterior insulation and finish systems (EIFS)—the original continuous insulation—can be used to successfully meet the requirements of building and energy codes.
Energy consumption of buildings
Engineering and management firm Morrison Hershfield aptly describes the impact of building energy usage in its Building Envelope Thermal Bridging Guide:
Space conditioning, primarily heating, is one of the largest components of energy use in commercial, institutional, and residential buildings in B.C. Building envelope thermal performance is a critical consideration for reducing space heating loads and will be an increasingly important factor as authorities strive for lower energy consumption in buildings. (For more information, consult the Building Envelope Thermal Bridging Guide – Analysis, Applications, and Insights by Morrison Hershfield Ltd. .)
According to Natural Resources Canada (NRCan), the residential sector accounted for 17 per cent of national energy use in 2013, with the commercial/institutional sector accounting for 10 per cent (Figure 1). (Further reading on these statistics is available at www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/energy/pdf/trends2013.pdf.) Total secondary energy consumption for all sectors was 8924 PJ. In the same year, space heating in the commercial/institutional sector accounted for 55 per cent of energy consumption, as shown in Figure 2.
Considering these statistics, reducing thermal bridging is more than a good idea—it is critical to reducing the impact buildings have on the natural environment.
History of energy codes in Canada
Energy codes and guidance documents have been available in Canada for longer than most people know. Now the National Energy Code of Canada for Buildings (NECB) is being adopted in many jurisdictions, it can no longer be relegated to a ‘nice-to-have’ or ‘best practice’ ideal.
According to a presentation delivered by Heather Knudsen of the National Research Council of Canada (NRC) in 2014, the need for energy efficiency guidelines for government buildings was first introduced in 1974. At the initial meeting of the Standing Committee on Energy Conservation in Buildings in November 1976, it was decided prescriptive requirements would be developed based on American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings. The first edition of “Measures for Energy Conservation in New Buildings” was published in 1978, with the second—including a new section for houses—released in 1983. Québec was the only jurisdiction to adopt the measures. In 1990, the Ontario Building Code (OBC) included insulation levels for houses from this 1983 document. (This historical information was taken from “National Energy Code of Canada for Buildings [NECB],” a presentation by Heather Knudsen, P.Eng., at the Manitoba Energy Code for Buildings [MECB] Training Day in September 2014. More is available at www.firecomm.gov.mb.ca/docs/necb_overview_sept2014.pdf.)
In 1997, the first national energy codes were published—one for buildings, and one for houses. The Model National Energy Code for Buildings (MNECB) was referenced in the OBC, and was used in numerous programs, such as Leadership in Energy and Environmental Design (LEED). This code used a prescriptive path for compliance, as well as an ‘engineered’ performance path with computer modelling. Performance requirements varied depending on both the fenestration-to-wall ratio and the energy source.
The next version of NECB was published in 2011, including changes such as a trade-off compliance path, increased performance requirements, and energy-neutral criteria. The improvement in energy requirements across all sectors after introduction of these changes averaged 26.2 per cent.
The newest version of the NECB was published in 2015. Due to provincial code cycles, this version has yet to be adopted across the nation. However, the NECB 2011 has been adopted by several jurisdictions, including:
The NECB 2015 pertains to all buildings apart from farm buildings and those covered by part 9—the latter are addressed in the National Building Code of Canada (NBC). Although the material presented here refers primarily to the NECB, energy efficiency concepts relating to exterior walls apply to all buildings.
Continuous insulation and thermal bridging
As code requirements increase, the benefits of using continuous insulation (CI)—such as cost-effective placement, minimal thermal bridging through opaque wall areas, and mitigation of condensation potential—are being recognized. However, the effect of thermal bridging has neither been adequately recognized, nor managed to reflect the actual thermal performance of wall assemblies by accounting for all of the thermal bridging inherent in standard wall construction.
As cited earlier, the most comprehensive document published on this matter to date is the thermal bridging guide produced by Morrison Hershfield and BC Hydro, which contains a comprehensive list of details with effective thermal properties evaluated using 3D modelling. According to the Building Envelope Thermal Bridging Guide:
It has become more and more evident that the thermal performance of the building envelope can be greatly affected by thermal bridging. Thermal bridges are localized areas of high heat flow through walls, roof, and other insulated building envelope components. Thermal bridging is caused by highly conductive elements that penetrate the thermal insulation and/or misaligned planes of thermal insulation. These paths allow heat flow to bypass the insulation layer and reduce the effectiveness of the insulation.
In the November 2016 issue of Construction Canada, an article by John R.S. Edgar entitled, “Improving Continuous Insulation,” examined the impact of thermal bridging on the effective thermal resistance (R-value or RSI) of CI in depth.
“The Morrison Hershfield research has shown this thermal bridging effect can reduce the effective R-value of the ‘clear wall’ by more than 30 per cent,” Edgar wrote. (John R.S. Edgar’s full article, “Improving Continuous Insulation,” was published in the November 2016 issue of Construction Canada. For more, visit the magazine website www.constructioncanada.net/improving-continuous-insulation.)
When CI is truly continuous (i.e. when it involves no thermal bridging), its benefit is fully realized. EIFS, designed and installed as a high-performance cladding solution, is the only continuous insulation and cladding system where thermal bridging is effectively eliminated. Most EIFS are anchored with adhesive, with no thermal bridging—unlike other claddings incorporating clips, anchors, support shelves, or girts.
“The contribution of details that are typically disregarded can result in the underestimation of 20 to 70 per cent of the total heat flow through walls,” according to the Building Envelope Thermal Bridging Guide, but this is not a concern with EIFS.
As a result of the evolving thermal requirements in the NECB, the critical path is the accounting for thermal bridging of assemblies that are not CI. No longer can an insulation riddled with structural penetrations be given its full value in designing for code conformity.
Keeping in mind the effects of thermal bridging, the new reality of the NECB must next be considered.
Meeting the requirements of the NECB
The NECB 2015 provides three paths for compliance. These are:
The prescriptive path provides specific performance criteria for each element in the building, including efficiencies for HVAC equipment as well as the maximum thermal transmittance values (U-values) for building envelope assemblies (i.e. walls, roofing, and fenestration).
The simple trade-off path applies to the thermal transmittance of above-grade building assemblies. With this path, the U-value of one assembly can be higher than permitted under the prescriptive path, while another is reduced—provided the overall U-value will not be greater than when following the prescriptive path. Vertical assemblies can only trade off with other vertical assemblies, and horizontal assemblies with horizontal.
The simple trade-off path thus allows for window-and-door-to-wall ratios (FDWR) to be increased, as long as the overall transmittance of the vertical assemblies does not increase as a result.
The performance path uses computer modelling to simulate the performance of the whole building. It requires the total energy consumption of the building not to exceed that of one constructed to the requirements of the prescriptive path.
Prescriptive path: Thermal performance
Figure 3 summarizes the prescriptive requirements for thermal performance of above-grade wall assemblies, extracted from Table 188.8.131.52 in the NECB 2015, providing maximum allowable U-values. It is more common for R-value or RSI to be the unit of measure used to evaluate thermal performance of building assemblies—the inverse of U-value.
Figure 4 provides an overview of the equivalent requirements for minimum overall thermal resistance, or the effective RSI required of wall assemblies. These are not nominal values, as would be assigned by considering only the frame-cavity thermal resistance.
Since the building industry is more familiar with R-values than RSI values, Figure 5 summarizes these values by climate zone. The imperial equivalent of RSI is as follows:
R-value (hrlsf F/Btu) = RSI X 5.678 (m2K/W)
It is important to restate that the RSI and R-values in Figures 4 and 5 are the effective values for wall assemblies, taking into consideration thermal bridging as discussed previously.
Using NRCan software called HOT2000, Figure 7 was developed to identify effective R-values of various wall assemblies with and without expanded polystyrene (EPS) as the CI. (Other software is available to calculate effective R-values as accurately, such as THERM—available at windows.lbl.gov/software/therm/therm.html.) These values include air films—an important factor, as indoor and outdoor air films on the surface of a wall marginally increase its thermal resistance. This table is by no means comprehensive, but is nonetheless a valuable tool to demonstrate the effect of framing on the overall thermal performance of the wall.
The yellow-highlighted row shows the effective R-value without stud cavity insulation and with only continuous insulation on the exterior. With 150 mm (6 in.) of EPS (RSI 0.68/25.4 mm [R 3.85/in.]), stud cavity insulation is not needed in Climate Zones 4, 5, or 6. This eliminates condensation risk in the stud cavity. This space could be used to run building services without concern of freezing or air barrier breaches (assuming the air barrier is on the sheathing, as would be required for EIFS).
In contrast to an un-insulated steel stud cavity wall, an insulated 150-mm (6-in.) steel-frame wall with R-20 batts does not meet the minimum required R-value of RSI 3.17 (R-18) for Climate Zone 4, and would not be acceptable for Climate Zones 5 to 8 either. This is because of the extent of thermal bridging through the steel framing—the effective R-value is only RSI 1.39 (R-7.92). However, by adding 57 mm (2¼ in.) of EPS, the minimum RSI/R-value requirement can be met for Climate Zone 4.
In the OBC—specifically, in SB-10, Energy Efficiency Requirements (and SB-12, Energy Efficiency for Housing)—there are tables of calculated solutions with CI for each of the three Climate Zones in the province. The tables provide prescriptive solutions to meeting the overall maximum U-values mandated by the code.
Figure 8 provides an excerpt of the insulation values contained in the OBC Tables SB5.5-5, SB5.5-6, and SB5.5-7, keeping only information pertaining to above-grade walls. CI is typically exterior insulation not interrupted by studs or other framing, including floor slabs. It can include, for example, EPS, extruded polystyrene (XPS), polyisocyanurate (polyiso), or other rigid insulation. Figure 9 summarizes R-values for EPS at varying thicknesses, using Figure 8 and Figure 9, it can be demonstrated R13 batt insulation between the studs, along with 95 mm (3 ¾ in.) of EPS, will meet the prescriptive requirements of steel-framed walls in Climate Zone 6.
In addition to the thermal characteristics of wall assemblies, critical consideration must be given to airtightness. Sections 3.2.4, Air Leakage, and 184.108.40.206, Opaque Building Assemblies, of the NECB require all opaque building assemblies to include an air barrier.
An integral part of EIFS is the liquid-applied air- and water-resistive barrier (WRB). Although this is not a requirement of either the Canadian Construction Materials Centre’s CCMC Technical Guide (The Technical Guide for Exterior Insulation and Finish Systems [EIFS] was published by the National Research Council of Canada [NRC] in 2006) or the Underwriters Laboratories of Canada (ULC) CAN/ULC-S716.1, Standard for Exterior Insulation and Finish Systems (EIFS) – Materials and Systems, many EIFS manufacturers test their WRB for airtightness properties—another feature of EIFS that, when designed and installed as a high-performance cladding system, easily surpasses the requirements of the the NECB in all Canadian climate zones. (For properties and test results of specific WRBs, it is best to consult the manufacturer.)
A key consideration for air barriers is the interconnection of the planes of airtightness from roofs to walls, walls to fenestration/doors, and walls to below-grade foundations. A robust design requires a would-be builder to manage the transition of materials and trade contractors at every interface of a building’s envelope. Air leakage testing for building commissioning is a growing method of validating building performance. (For information on standards for airtightness testing, visit the National Air Barrier Association at www.naba.ca and the Air Barrier Association of America at www.airbarrier.org/whole_building/index_e.php.) Though this testing was first devised as a method of certifying R-2000 homes in the 1980s, recent developments in Canada Green Building Council (CaGBC) and U.S. Green Building Council (USGBC) circles, ASHRAE, and building science consultants are working toward standardizing methods and processes as part of the evolving business of commissioning building envelopes for commercial, institutional, and multi-residential projects. (This information was taken from the “Building Science Roundtable” in February 2016, edited by Ted Kesik.)
Meeting code requirements with EIFS
Stretch codes are pushing the minimum requirements for building energy performance, meaning thermal performance is increasing. (Upcoming code changes can be viewed at www.nrc-cnrc.gc.ca/eng/solutions/advisory/codes_centre/public_review/summary.html.) Concurrent to code evolution, understanding and accounting for thermal bridging is becoming commonplace. Building designers specifying EIFS as a high-performance cladding solution can meet the NECB more effectively, economically, and ecologically than with other cladding choices. (More information can be found in “Sustainable Cladding Choice Equates to High-performance Building Envelopes,” an article released in Construction Canada’s January 2016 issue. It can be found at www.constructioncanada.net/sustainable-cladding-choice-equates-to-high-performance-building-envelopes.)
As summarized by Edgar, a truly continuous insulation improves the longevity and performance of the building by eliminating thermal bridging and, therefore, also condensation, air movement, and building movement induced by thermal shock. A high-performance, EIFS-clad wall assembly incorporates an integrated air barrier, and where an increased window-to-wall ratio may be needed, EIFS’ insulation thickness can be increased to accommodate. EIFS has the additional advantage of providing distinct exterior finishes, which can be made to look like masonry, stone, metal, or other appearances while providing the benefits of CI with an air barrier. EIFS is CI, and lacks thermal bridging. Combined with its versatile appearance and service life of 50 or more years, this makes it invaluable in meeting the requirements of the country’s energy codes.
Amanda Sinnige is the manager of technical services for Dryvit Systems Canada, having joined the company in early 2015. She has worked in the field of building science for the past 26 years, concentrating her efforts on the energy performance of buildings, sustainable construction and renewable energy, and the impact of these on the performance of the building envelope. She can be reached via e-mail at email@example.com.
Kevin Day, LEED AP, is the vice-president of sales and marketing for Dryvit Systems Canada. He is the chair (and past-president) of the Exterior Insulation and Finish Systems (EIFS) Council of Canada, and a past-president of the Ontario Building Envelope Council (OBEC), winning its 2014 Anthony A. Woods Award. Day is regarded as a leading expert on EIFS, and is widely recognized for his extensive cladding engineering experience. He is a frequent contributor to Construction Canada. He can be reached at firstname.lastname@example.org.
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