EIFS and sustainable design

by Elaina Adams | January 1, 2013 8:03 am

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By Dale D. Kerr, M.Eng., P.Eng., BSSO, and Tom Remmele, CSI
Exterior insulation and finish systems (EIFS) can economically provide energy efficiency and reduced carbon dioxide (CO₂) emission levels. (An earlier version of this article appeared in the August 2007 [2]issue of The Construction Specifier, the official publication of the Construction Specifications Institute [CSI]). However, without durability as the cornerstone of sustainable design, most other ‘green’ attributes of products or systems are lost. Fortunately, with proper installation and integration, these cladding assemblies also offer long-term performance and durability.

From an architectural perspective, EIFS offer the ability to replicate almost any architectural style or finish material, coming in myriad shapes, colours, and textures. Low in cost and lightweight, they can be installed over existing buildings—this reskinning allows design/construction teams to reuse the original shell instead of demolition and introduction to the waste stream.

Further, a building’s overall energy performance and interior environment can be greatly improved by placing the insulation on the outside of the building. This strategy minimizes thermal bridging and helps keep the structural members at a consistent temperature, improving their expected longevity.

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By keeping the temperature of structural members constant, they are less susceptible to the movement and stress caused by temperature swings that could lead to cracking in concrete, masonry, and stucco walls. (In turn, this cracking could lead to water penetration and degradation, such as spalls or corrosion.)

Additionally, with sufficient insulation outboard of the structure, a dewpoint is eliminated and the potential for condensation from vapour diffusion is minimized. Mould, corrosion of metal fasteners and framing members, and deterioration of batt insulation and its R-value are a few of the potential effects of condensation that can be avoided.

Traditional, or ‘face-sealed,’ EIFS assemblies have typically consisted of five components:

• insulation board;
• adhesive and/or mechanical fastener to attach the insulation board to a substrate;
• reinforcing mesh for impact resistance;
• base coat to embed the reinforcing mesh and provide weather resistance; and
• decorative and protective finish coat.

While traditional or face-sealed EIFS were associated with some water intrusion issues in the residential industry, it is important to note the materials themselves were not the root cause. As buildings were made tighter and more energy-efficient, they became somewhat less forgiving of poor workmanship and water damage became more frequent.

Windows (and their installation) have also been a source of leakage into walls. This, combined with poor construction practices and tighter building envelopes, can affect durability, regardless of the cladding—brick, stone, EIFS, concrete, wood, or vinyl siding.

New generation of EIFS
In response to these water intrusion issues, building wraps or asphalt-impregnated sheathing paper and felts were installed behind EIFS to provide moisture protection to the wall structure. These wraps are relied on for providing water resistance, but they are often punctured and/or have the potential for tearing and mislapping during installation. As they are not fully adhered, they are also susceptible to billowing under wind load, which affects the wall’s pressure equalization performance.

Further, where sheathing paper, felt, or building wraps are used, mechanical attachment of the EIFS becomes necessary, as the specialized adhesives do not stick to sheet goods. Mechanical fasteners create thermal bridges, rendering EIFS less thermally effective. (The fasteners can cause ‘ghosting’ through the finished wall surface.)

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Newer EIFS products can overcome the limitations of traditional moisture protection and mechanical fasteners. These materials incorporate a fluid-applied waterproofing membrane and air barrier directly applied to the sheathing behind the EIFS wall covering (Figure 1). Rather than simply a cladding, these systems can be considered a complete exterior wall assembly, providing multiple building envelope functions.

Weather barrier
Most exterior wall problems are caused by water, primarily rain. When water gets into the wall system and wets the assembly’s materials, it can accelerate deterioration of those materials and create conditions conducive to mould growth, compromising indoor air quality (IAQ).

When the wall is designed to prohibit rainwater penetration, durability is drastically improved. In an EIFS wall, the lamina (i.e. base coat, mesh, and finish coat) acts as the initial defense against rain. Any joints in the exterior wall system, such as those between dissimilar materials, must be designed to resist rain penetration. Joints and flashing should be designed and constructed to slope toward the outside of the wall to prevent gravity flow of water inwards. Where appropriate, two-stage joints, drip edges, and capillary breaks should be incorporated to avoid inward water movement.

Water-resistive barrier
Incorporating a secondary means of controlling rainwater penetration—a water-resistive barrier (WRB)—can be beneficial in both preventing damage during construction, and keeping the building interior dry even before the lamina cladding is installed. In other words, this improves the wall’s long-term durability.

In the case of some newer EIFS styles, fluid-applied waterproofing applied to the substrate serves as the WRB; its purpose is to stop water getting past the lamina and insulation.

Newer proprietary EIFS products also provide an air cavity behind the insulation. Depending on the manufacturer, this may involve use of slots cut into the insulation and/or vertical ribbons of adhesive. Regardless, such air cavities provide a drainage space—should water get through the outer EIFS surface at a crack, it flows downward via gravity. Flashings installed strategically at floor lines and at the wall’s base direct the water back outside the wall where it cannot damage internal components.

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Thermal barrier
By incorporating a thermal barrier within the building envelope, it is possible to minimize heat flow between the inside and the outside, allowing interior conditions to be maintained at a comfortable temperature.

In conventional frame wall construction, batt insulation is placed within the stud space to provide the thermal barrier. Improved thermal resistance is achieved by increasing the studs’ thickness, allowing thicker insulation to be used. However, as the studs are exposed to both the inside and outside environments, they conduct heat at a much higher rate than the insulation, creating multiple thermal bridges.

As the first two letters in the EIFS acronym suggest, insulation is applied to the exterior of the building frame, eliminating the multiple thermal bridges. The thickness of the insulation can be significantly increased to make even more dramatic increases to the R-value and the wall’s thermal efficiency.

Air barrier
Required by the National Building Code of Canada (NBC) since 1985, air barriers prevent air leakage through the building envelope, helping to stop exfiltration of heated air to the cold exterior and the infiltration of cold, untreated air to the interior. The result is a much more thermally controlled environment requiring less energy input to maintain.

Stopping air leakage prevents the second most common source of moisture in a wall assembly—condensation. In a cold climate like Canada, as warm humid air from inside a building moves through the envelope, air cools until it is no longer able to hold its moisture. The moisture condenses on the first cold surface within the wall assembly below the dewpoint of the air (often the back of the exterior sheathing).

A structural, durable, continuous, and air-impermeable barrier throughout the building envelope can prevent air movement across the envelope. The fluid-applied membrane of some newer EIFS assemblies meets all these requirements. Being fluid-applied makes certain any joints or gaps are filled, helping to ensure continuity. Where necessary, compatible sheet materials or sprayed foams can bridge larger gaps between different materials within the wall (e.g. junctions with windows or doors). As it is fully adhered to the substrate, the fluid-applied membrane becomes an integral part of it, assuming the strength of the substrate and the ability to resist pressure differences caused by wind, stack effect, or mechanical systems. The membrane is located on the interior side of the insulation in an EIFS wall, so it is protected from the exterior elements, helping ensure longevity.

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Avoiding the double vapour barrier
For conventional frame-wall construction in a cold climate, a polyethylene vapour barrier is typically installed behind the interior gypsum wallboard. Alternatively, special vapour barrier paint can be applied to the drywall surface. Some design professionals may be concerned the aforementioned air barrier/waterproofing membrane found in some newer EIFS assemblies could also function as a vapour barrier, creating a ‘double-vapour-barrier’ situation. While this may be a problem with some waterproofing and air barrier materials, the products used in EIFS are generally vapour-permeable and thus permit diffusion and drying. (It is always important for the design professional to discuss system properties with its manufacturer.)

The accepted definition of a vapour-retarding material is one with a water vapour permeance of 57.4 ng/(Pa•s•m²) or 1 perm. A 0.1-mm (4-mil) polyethylene product is 4.6 ng/(Pa•s•m²) or 0.08 perms, and No. 15 building felt is at about 325 ng/(Pa•s•m²) or 5.7 perms. Some EIFS water-resistive barriers have a vapour permeance equivalent to building felt, while others can be slightly higher or lower, depending on the manufacturer. As long as the EIFS water-resistive barrier has vapour permeability significantly higher than the interior vapour retarder, the ‘double vapour barrier’ does not exist. Consequently, it should not be a concern in a cold climate, provided bulk water is kept out of the stud cavity (which should always be the case in any durable wall design).

Conclusion
Exterior insulation and finish systems contribute to sustainable design in several ways:

• longevity and lifecycle analysis (LCA);
• reuse of existing building shells;
• optimization of energy performance;
• reduced carbon emissions; and
• components low in volatile organic compound (VOC) emissions. (The importance of a low-VOC product on the exterior is not only the health and safety of the applicators, but also the low carbon dioxide emissions.)

Further, as illustrated throughout this article, EIFS assemblies can be multifunctional and highly effective systems. As demonstrated by the effective R-value of these systems and the moisture protection they provide, EIFS can be an important component of an overall sustainable design strategy effective in achieving building envelope and operating efficiency.

Dale D. Kerr, M.Eng., P.Eng., is a principal at engineering firm, GRG Building Consultants. She has more than 20 years of experience in building science research, testing, failure investigation, and building repair. Kerr was the first to be recognized as a Building Science Specialist of Ontario (BSSO) by the Ontario Building Envelope Council (OBEC) and is a regular contributor to technical publications across North America. She can be contacted via e-mail at dkerr@grgbuilding.com.

Tom Remmele, CSI, is the director of technical services/R&D for exterior insulation and finish systems (EIFS) producer, Sto Corp. He has held technical management positions in the construction industry for more than 20 years. Remmele is a past Technical Committee chair of the EIFS Industry Members Association (EIMA) and is a member of the Construction Specifications Institute (CSI) and the ASTM Committee E6 on Building Performance. He has published numerous technical articles on EIFS, air barriers, stucco, and related topics in technical journals. Remmele can be contacted via e-mail at tremmele@stocorp.com.

For more on EIFS and sustainable design, click here[7].

Source URL: https://www.constructioncanada.net/eifs-and-sustainable-design/

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