| What is Insulation - What is an Air Barrier |
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Most people think insulation is a product or material. Insulation works because it incorporates air pockets that resist the flow of heat. It slows the conduction of heat. This resistance to heat flow is measured by the R-value of the material. Unfortunately R-values do not account for air movement through materials.
What's Your Image of Insulation? Most people think of fiberglass. Some think of cellulose. More are becoming aware of foams. In reality these materials are just a vehicle to trap air. The material is attempting to create tiny pockets of air that slow the transmission of heat. Some materials do this better than others. Fiberglass and cellulose are air permeable, they allow air to flow through them. This requires that they be in direct contact with an air barrier. The advantage of foam is that it performs as both an air barrier (to stop convection) and as a thermal barrier (against conduction). Most insulation products do not stop air flow. Spray foams are an exception because they create their own air barrier. Excerpted from TBC Guide
Figure 1.1.1 – Most insulation does not stop the flow of air. Thus, for most insulation to be effective, a separate air barrier or skin is needed to stop the flow of air (Figure 1.1.2). For the air barrier itself to be effective, it must be contiguous and continuous across the entire building envelope, with all holes and cracks fully sealed, and it must be perfectly aligned with the insulation (Figure 1.1.3).
Figure 1.1.2 -Air barrier prevents the flow of air through insulation.
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