Sheathings reach beyond the code

by Elaina Adams | March 1, 2012 11:12 am

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By Janelle Day, B. Arch. Sc.
The Canadian government recently suggested energy efficiency is an important tool for addressing climate change, promoting economic activity, and supporting energy security. (See the Natural Resources Canada (NRCan) report, “Government of Canada Recognizes Energy Star Leaders,” from June  2010. For more information, visit www.nrcan.gc.ca/media-room/news-release/37/2010-06/1435[2]). Further, it says Canada will aim to reduce greenhouse gas (GHG) emissions by 17 per cent below 2005 levels by 2020. Since 2006, the federal government has invested close to $10 billion in an effort to reduce GHG emissions; this is being reflected through investments in green infrastructure, energy efficiency, and the building industry.

New energy efficiency provisions for housing and buildings are included in the updated National Building Code of Canada (NBC). Scheduled to be released in the spring, it will continue to change the way we build in Canada. As this push for energy efficiency continues to grow, builders are looking for new innovative systems to help them meet the code’s new requirements and to reach beyond to higher voluntary energy efficiency levels of the next-generation Energy Star and R-2000 standards.

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Integrating the air barrier system
Builders have begun exploring systems that use exterior insulated sheathings (EIS) in wall assemblies to help them achieve higher levels of energy efficiency. When properly detailed, EIS becomes a part of an air barrier system that can effectively reduce air passage. An air barrier system controls the amount of air moving through the building envelope either inward or outward. To provide this control, the air barrier system must block all leakage openings and extend across intersections where interior walls meet an exterior wall, ceiling, floor, or roof.

To be effective, an air barrier system must:

• satisfy several requirements;
• be continuous;
• have sufficient structural strength to resist wind loads;
• be constructed using materials and components that are airtight; and
• be durable to last at least as long as the building.

New code requirements also demand all tape and caulking be compatible with the primary air barrier component. If an air barrier system does not meet these requirements, then the building may experience:

• moisture damage;
• cold drafts;
• high energy bills; and
• gradual deterioration over time.

EIS, together with gasketing and tape, has been shown to create an effective air barrier system, thereby avoiding these issues. Some of these innovative systems have also been evaluated by Canadian Construction Materials Centre (CCMC) and carry a listing and report attesting to system performance and durability.

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How it works
With an exterior insulating air barrier sheathing (EIAS) system, the sheathing is applied to part of the outside of the building frame, using conventional and readily available construction products (i.e. gasketing and tape) to control air leakage. It uses a compression-type seal to achieve extraordinary levels of airtightness and durability. However, the real innovation of this system is its ability to fulfil multiple functions within the wall assembly. The system saves energy because it controls heat loss by insulating and reducing thermal bridging. It also lowers the potential for condensation caused by air leakage, and minimizes potential for moisture damage by controlling ingress of outdoor wind and rain into the wall assembly. This type of system is best suited for the low-rise residential market as it can replace conventionally used sheathing components to maximize performance.

Planning the air barrier system’s installation is an important first step that should never be forgotten when building. Considering the details before construction enables the work to go smoother and the quality of construction and productivity to improve. One should always consider the relationship of construction sequence to the air barrier system details. Minor adjustments to the construction sequence can significantly simplify air barrier system installation. Planning should consider:

• installation of all panel joints and gaskets;
• construction of outside corners to avoid using scaffolding; and
• construction of inside corners to allow proper sealing.

When using any type of system, mishaps and errors happen. However, there are easy ways to correct them to maintain air barrier continuity and control air leakage with an EIAS system. Penetrations through the air barrier system have to be sealed to ensure optimal system and wall assembly performance. With this type of air barrier, it is not necessary to seal the interior polyethylene wall vapour barrier to make it airtight. The required continuity of the air barrier plane is achieved on the exterior side of the wall with the sheathing and components. The polyethylene on the interior side in this instance only acts as a vapour barrier and need not be sealed.

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In planning for construction, there are many areas of the air barrier system that require proper detailing to work effectively. Any leaky areas of the envelope can compromise the entire air barrier system. For example, wood and gas fireplaces and stoves can penetrate the air barrier where they vent, and sometimes where they are installed. To resolve problems such as this, wood frame walls should extend around all of these appliances, including around their chimneys and vents. This will provide numerous advantages beyond simplifying the air barrier system installation.

The building’s thermal insulation is substantially improved with the insulated house frame wall extending around the appliance, resulting in energy savings. Additionally, the approach keeps the flue of the appliance warm, improving venting for those appliances which rely on natural draft. When correctly installed, and with proper detailing, an EIAS system can provide many benefits.

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Marketability in today’s industry
As a multifunctional system, it can also provide additional benefits to the homeowner. Cold drafts can be virtually eliminated in houses using this system, helping increase occupant comfort. The system provides long-term performance by using a mechanical seal to reduce the incidence of moisture-laden air leaking into insulated envelope cavities. When coupled to an efficient mechanical ventilation system, an EIAS system can enhance indoor air quality (IAQ). Further, this system can withstand wind loads typically encountered in a three-storey building. This helps ensure the air barrier system is effective over the house’s life and remains unaffected by extreme weather conditions. The improvement in energy efficiency results in lower heating and cooling energy costs.

Aside from the building science innovation associated with the system, it also promises to substantially reduce labour and material costs. There are numerous benefits for onsite installers when this type of system is used:

• the polyethylene vapour barrier does not need to be sealed;
• there are fewer penetrations to seal compared to polyethylene or airtight drywall (i.e. warm-side air barrier systems);
• it can be an effective weather barrier and sheathing membrane (building paper may be omitted); and
• the system uses commonly available materials, such as extruded polystyrene (XPS) wall insulating sheathing, polyethylene, and sill-plate gasketing.

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The system results in a better performing wall assembly at a cost equal to or lower than that of a conventional assembly. For example, two options for reaching an R-24 (RSI-4.23) wall would be through regular R-19 (RSI-3.34) batt coupled with exterior insulating sheathing (R-5 [RSI-0.88]) or through high-density R-24 batt. In comparing these two assemblies, the EIS would result in a more cost-effective route. Properly installing an air barrier system requires attention be paid to all aspects of the building details. Good air barrier systems need not be costly or difficult to build, but they do require special care in ensuring the right materials are used and the system is continuous.

Reaping the rewards
The EIAS system offers the flexibility of different options to create an air barrier system customized to the builder’s needs. By maximizing envelope performance and cost savings, those implementing these systems are differentiating themselves as leading green competitors without introducing substantial changes to their production process. Builders are able to compare the performance of their standard production to different iterations of this new system, one house at a time. They are also able to identify the performance improvements that can be achieved.

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Exterior insulating air barrier sheathing is a complete system that can help builders save time and money, and delivers durable, dependable comfort and energy efficiency to homeowners. As the government pushes to reduce GHG emissions and build a more sustainable environment, energy efficiency continues to be a priority. With the new provisions for housing and small buildings coming into effect, builders are responding by exploring systems such as the EIAS to help them reach beyond the requirements. Improving energy efficiency in buildings will continue to be a government priority to reduce carbon emissions. Exploring innovative building systems keeps design professionals at the forefront, ready to address and adapt to changes.

Janelle Day, B. Arch. Sc., is the technical co-ordinator at Lio & Associates. She currently works with builders to evolve exterior insulating air barrier sheathing (EIAS) into a system completely tailored to each builder’s production methods and trades. Day’s work with mentoring is helping to identify the differences in construction and the improvements in performance that can be achieved. She can be contacted via e-mail at support@mlio.ca.

Source URL: https://www.constructioncanada.net/sheathings-reach-beyond-the-code/

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