Air Barrier Systems: Advantages & Disadvantages
In Winnipeg, an Air Barrier system must:
In Winnipeg, an Air Barrier system must:
- eliminate air movement through the building envelope
- be continuous over the entire building enclosure
- be robust enough to withstand its environment and forces applied
- be durable
Air barrier systems are created in numerous ways:
- exterior air barrier membranes - blueskin used on commercial applications
The advantage to the blueskin membrane is that it self adheres, does not release and is continuous when properly installed. Its disadvantage is primarily its cost. In Winnipeg, it is not cost effective for most home owners. It is therefore generally used only in Commercial applications. Another potential problem in Winnipeg is being installed on the exterior of the wall, it does nothing to prevent differential pressure from moving moisture laden air into the wall from the interior of the building.
- Exterior applied rigid foam panels
Exterior rigid foam panels form a continuous insulating layer which when newly and properly installed form an air barrier system that is impenetrable to the effects of wind pressure and resultant heat loss. This is a significant benefit in Winnipeg. The main disadvantage is that the system relies on the resilience of adhesives and sealant caulking which yield over time allowing air movement around the panels. Additionally rigid Foam Panels do not prevent moisture laden interior air from moving into the wall cavity.
- interior air barrier membranes - 6 mil polyethylene
The main advantage to 6 mil polyethylene sheet is that it is widely accepted in Winnipeg and is inexpensive. It also prevents moisture laden air from entering the wall cavity through the interior side of the wall assembly. The disadvantages is that it is dependent on adhesives and sealants which fail in time and it is subject to penetrations at time of construction and by occupants who hang paintings, or make changes to their interiors. Because it is applied to the warm side of the wall assembly in Winnipeg, it does nothing to prevent wind pressure or vapor pressure from moving moisture laden air into the wall cavity from the exterior side of the wall. Over the life of a building, it performs as a poor air barrier.
- interior air barrier through gypsum board
Gypsum board as an air barrier is a difficult assembly to create because it requires a level of attention to detail that most contractors and tradesmen fail to provide. Top and bottom plates, rim joists and sub floor, ceiling board, sill plates must all be caulked, glued, taped, or sealed with gaskets prior to installation. This is an air barrier system which will only perform with extreme attention to detailing as it is installed and therefore generally fails to meet its performance criteria even when just installed. In time, due to Winnipegs climate, these sealants release causing drywall to perform as a poor air barrier.
- cavity filled spray foam insulation
Spray Foam insulation is an effective air barrier system, surpassing the National Building Code of Canada's specification (the most stringent in the world) with an air permeance of less than 0.02 l/(s-m2) @ 75 Pa. Acting as an air barrier, vapor barrier and insulation layer in a single application, material drying is not a factor as spray foam insulation is impermeable to moisture. The main advantage to spray foam is that it is 'custom fit' - adhering to and formed specifically for the space into which it is applied. It requires no detailing or other special care, it never settles, sags, or degrades in performance. Spray foam insulation is the best air barrier available in Winnipeg.
Unlike other air barriers which are designed to protect a fibrous insulating material, insulating foam is not subject to moisture ingress from either the warm or cold side of the wall and thus moisture accumulation and damage is not an issue. This is a very significant benefit to using foam in Winnipeg. Spray foams main disadvantage is its perceived cost. While up front it is more expensive, the long term impact on ownership costs result in savings to homeowners who choose spray foam insulation.
by: Mark Nelson
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