How to Select an Air Barrier

Air barriers work by blocking unwanted or escaping air movement through building cavities, preventing air leakage around your home. Further, they help to control moisture in your home, allowing water vapour that enters to diffuse back out.

There are various factors that need to be considered when choosing an air barrier material, and the selection of the correct material will directly depend on the personal needs of your home.

Here's how to select the right air barrier for your home

Air barriers have a variety of benefits including controlling the circulation of air in your home which can lower heat and energy costs while preventing risks such as condensation buildup and mould growth. Also, many materials that most homeowners already know, as they are used for structural purposes, can act as air barriers too. 

Air barrier membranes are categorized per their permanence to water-vapour, but choosing one is climate-dependent. In humid climates, you might consider using a combination air barrier and vapour diffusion, as not all air barriers are completely water-resistant.

However, in drier climates, traditional air barriers should work just fine. Certain types of insulation, including foam board and dense cellulose, can be effective at reducing heat and airflow. Bear in mind that fibreglass insulation does not stop air leakage. Air movement is easily recognized on dirty fibreglass, as it works to collect particles in the air like a filter.

Several factors must be considered when selecting an air barrier, and these include UV resistance, insulation being present in the cavity, insulation being present outside as well as water storage capacity of the sheathing. Further, the wall type in which the membrane will be installed must be considered, as well as home design and personal budget.  Here are some of the air barrier options on the market, to be installed alone or alongside fibreglass insulation.

House Wrap

source: Flickr, Hibbs Homes

The most common air barrier material is house wrapping. This material is generally installed during a house's construction, wrapped around the exterior of the building's structure. Certain wraps are made to withstand water better than others, and further, these materials come in a variety of sizes for different purposes. The most common house wraps are made out of a fibrous spun polyolefin plastic matter that comes in rolled-up sheets. Depending on the manufacturer or brand, house wraps may also consist of or have alternate materials woven through them to prevent tearing.

House wraps as air barriers should be avoided in wet climates, as they sometimes react with certain kinds of wood siding. These types of wood siding, such as redwood and cedar, have a naturally occurring substance called Lignin.

Lignin acts as a detergent and unfortunately decreases surface tension, destroying the house wrap's ability to repel water. To prevent this from happening, attach heavy building paper to the walls in place of house wrap. Felt paper is another option, but must be installed alongside house wrap for an effective air barrier. 

Continuous Air Barrier Options

House wrap is an effective air barrier, but it may not be necessary for you to rip out the walls of your home to install it. Again, this greatly depends on the individual needs of your home, and most importantly, the amount of air leakage. If you only have a minimum amount of leakage, it would be worth considering using a sealant to seal any open holes or seams.

To do this use durable caulk or other spray-able foam sealants. If you have already installed house wrap, but are finding holes between the sheets, it is recommended that you go over the job with sealing tape, sometimes referred to as “house wrap tape.” Most house wrap manufacturers have a specific tape for this purpose. 

Air Barrier and Vapour Diffusion Combinations

source: Flickr, spray foam experts

For homes that are located in areas with high levels of humidity, air barrier and vapour diffusion combinations are available. These materials combine water vapour diffusion with air movement control and are specifically designed for keeping humid outdoor air from entering into their building cavities.

In most cases, air barrier vapour diffusion combinations consist of polyethylene plastic sheets, builder's foil, foam board insulation or other exterior sheathing materials. Make sure to do plenty of research regarding material specifics before selecting one for your home!