Architects have a broad range of choices where selecting air barrier products to employ in building design. Spray foam insulation products can provide superior performance and also contribute to greater energy and operating cost savings in building that’s why they are often selected. These products are the first alternative chosen by architects when designing exterior walls for airtight construction.
What are Air Barrier Systems?
Air barriers are systems of materials designed to control airflow between a conditioned and an unconditioned space. The primary air enclosure boundary that separates indoor (conditioned) air and outdoor (unconditioned) air is the air barrier system. In a multi-unit/apartment/townhouse construction the air barrier system separates also the conditioned air from any given unit and adjacent units. Air barrier systems define the location of the pressure boundary of the building enclosure. The air barrier system in a multi-unit/apartment/townhouse construction is also the fire barrier and smoke barrier in inter-unit separations. Also the inter-unit separation must meet the specific fire-resistance rating requirements for the given separation. The air barrier system is also the “gas barrier” that provides the gas-tight separation between a garage and the remainder of the house or building.
Air barrier systems can be located anywhere in the building enclosure, at the interior surface, the exterior surface or at any location in between. Interior air barrier systems in cold climates control the exfiltration of interior often moisture laden-air. Exterior air barrier systems control the infiltration of exterior air and also they prevent wind-washing through cavity insulation systems. Air barrier systems are able to withstand the forces that may act on them during and after construction and are durable over the expected lifetime of the building.
The importance of Air Barriers
The air within the envelope of a building is subject to air infiltration, exfiltration and the three modes of heat transfer: convection, conduction and radiation. Insulating materials address heat transfer through all three modes but sometimes the benefits can be lost completely if air infiltrates the envelope. Combined with spray foam, batt and rigid insulation air barriers can provide a solution, plus additional thermal performance (R-Value) for houses and commercial buildings when installed facing an enclosed air cavity and/or air film. The polyethylene and aluminium components used in many air barriers act as vapor retarders and the combined effect reduces the heat transfer and moisture within the building envelope. Now with advanced technology in vapor transmitting air barriers, exposed walls are able to dry when needed to reduce the risk of moisture accumulation.
The benefits of Air Barriers
In summer we normally dehumidify and cool the air to a lower temperature and humidity than the exterior environment. While in winter we heat and humidify the air to a higher temperature and humidity than the exterior, controlling interior temperature is paramount to comfort.
- Prevents the loss of conditioned air – Reports show that over 30-40% of the cost of heating and cooling a home is lost to uncontrolled air leakage. And this can hamper the performance of other building systems such as HVAC and insulation.
- Prevents moisture – Proper air sealing reduces the risk of water vapor moving into the wall system which can result in moisture issues such as mold etc. Air leakage transports exponentially more moisture into and through the building enclosure than occurs through vapor diffusion alone.
- Lower utility bills – Maintaining conditioned air means less energy is needed to recondition the air and less energy means lower utility bills. The savings can add up since all building systems must perform well together to optimize the energy efficiency of a home.
- Indoor air quality – Air barrier systems help keep out pollutants such as allergens, insects, dust, noise and more.
Where to install an air barrier
Unlike the vapor retarder, the air barrier can be located anywhere in the enclosure assembly. The air barrier if it is placed on the predominantly warm, humid side (high vapor pressure side) of the enclosure, it can control diffusion as well and also would be a low-perm vapor barrier material and it is called an “air and vapor barrier”. In case that is placed on the predominantly cool drier side ( low vapor pressure side) of the wall, it should be vapor permeable, 5-10 perms or greater. For external insulation air barrier systems are used different materials such as: concrete panels, breathable insulated structural sheathing products and self-adhering membrane sheets. Houses that are built with old codes often have no air barrier installed and this leads to all sorts of problems with air infiltration, moisture, drafts and other uncomfortable and potentially damaging weather-related issues.
- Interior Air Barriers – can be applied on interior door frames and windows, the connecting points of walls and ceilings, joists as well as a variety of other areas. These kinds of barriers tend to have moisture-reducing capacities that are more pronounced than their exterior air barrier counterparts.
- Exterior Air Barriers – can be applied to the outside of a building, exterior air barriers carry a few advantages over their interior counterparts. Their installation process is far less intrusive into the day-to-day life of building occupants. Unlike the interior air barriers, the exterior air barriers are also designed to be better at wind-resistance rather than moisture-resistance. A building can utilize both interior and exterior air barriers to make an effective guard against elements and create a better sealing system overall.