On a project currently under construction we discovered the improper installation of the vapour barrier at electrical outlets done during a previous renovation. The vapour barrier is not sealed to the outlet using a pre-manufactured outlet box. Instead there are numerous holes for air and moisture to enter and exit the home through the exterior wall. This can lead to mould and rot issues.
When on site reviewing projects under construction we review to ensure that contractors conform to the requirements of the contract documents (a.k.a. drawings and specifications). Two of the most important items to review for proper installation are the air and vapour barriers. These two membranes work hand-in-hand with properly balanced heating and cooling systems and their continuity are critical for providing an air-tight home, reducing risk of mould, and decreasing energy consumption.
According to John Straube, principal of Building Science Corporation and professor at the University of Waterloo in Ontario, air leaks can be responsible for up to one third or more of the energy loss of a home. Air leaks are caused by pressure differentials between the interior and exterior of the home. These differentials are caused by three factors: wind, fans and the stack effect. For example, when wind pushes on the house the leeward side becomes negatively pressurized, drawing warm, damp air from inside the home out through holes in the walls. When this warm, damp air is drawn through the exterior walls of the home, if it is colder outside than it is inside the water vapour in the air will condense inside the wall. Over time this can cause mould and rot. Similarly, the stack effect works on the principal that warm air rises. Like a large chimney, air and heat will escape through holes and cracks of the roof of a house based on the upward air movement. If not sealed properly, moisture can build up in attic and ceiling spaces.
To ensure adequate ventilation, typically an HVAC designer – or mechanical engineer – is engaged to ensure the house is properly “balanced.” They calculate their air required to heat and cool the house and the air that is required to replace any air extracted by household fans, appliances and equipment. They size and place ducts, registers, air returns, fans and equipment. They run calculations based on rooms sizes and heights, and assemble an overall package of products, drawings and information. In Toronto, all of these calculations and drawings are required for a Mechanical Building Permit. When the new equipment is installed and the house is sealed, the drywall painted and all of the exterior cladding is on, the mechanical contractor can then fine-tune the system and balance the house.
Hand-in-hand with the balancing of the air systems is the proper installation of the air and vapour barriers to reduce air leakage. When reviewing a home under construction, we look at the installation methods the contractor is using to see if the continuity of the vapour and air barriers is being maintained. We also look at locations around windows, doors and other openings and typical “problem spots” such as the connections between materials, corners, joints, vent stacks, electrical outlets and light fixtures to review how these have been installed. If improvements can be made, the contractor is notified. We look for minimum overlaps between pieces of air and vapour barrier, use of primers (if required), evidence of air and acoustic sealants at splices, edges and penetrations, and use of Tuck Tape or other special purpose tape at membrane edges. All of these components at all junctures are critical to ensure success and minimize air leakage. As part of our role, we review to see if the contractor is conforming to these requirements.
Air leakage through the exterior walls of the home not only affects thermal performance but can also lead to mould and rot of building materials. It can affect the longevity of the home, but can also adversely affect indoor environment quality. Proper installation of air and vapour barriers, as well as balancing of heating, cooling and ventilation systems will help minimize air leakage and provide a healthier, longer lasting home.
If you have any questions about air and vapour barriers; HVAC design; system balancing; or how an architect can help with your home renovation process, feel free to drop us a note.