Bob Hill, PE
August 2, 2012
Don't Get Caught in A Tight Spot - Pay Attention to Air Sealing
As jurisdictions begin adopting and enforcing the 2012 IECC, the need to pay particular attention to air sealing will come to the forefront. The 2012 IECC requires that each home have a blower door test and that the resulting ACH50 value be less than 3 (less than 5 in climate zones 1 & 2). For those not familiar with the terminology, ACH50 denotes the number of Air Changes per Hour that a home will experience if the pressure differential between the outside and the inside is 50 Pascals, which is only 0.00725 pounds per square inch or 0.20 inches of water. It may seem insignificant, but it is more than enough to cause air to easily leak into most homes. A wind speed of 20 mph might create this type of pressure difference.
Some especially energy-conscious builders have been very successful in building tight houses, but typical new construction probably has ACH50 values of about 7. Getting a home down to below 3 takes considerable effort. Green home builders are generally very energy conscious and concerned about air infiltrations but even among the homes we have certified to the ICC 700 National Green Building Standard (NGBS) that were blower door tested, fewer than 29% of them would have met the 2012 IECC requirement. This puts the new code in perspective. Since blower door tests are usually not conducted until a home is essentially completed, a failing test is a major problem for a builder to correct as corrective action is often needed behind the drywall. It pays to make sure everything is done right the first time and attention to detail is critical.
Over the last couple of years, product manufacturers have been investigating how their products impact air infiltration and many have come to Home Innovation Labs’s lab to have their products tested. The Home Innovation has an air infiltration test chamber that measures air leakage through full-size wall assemblies following ASTM E283. A typical wall construction may contain framing, sheathing, window and door openings, other penetrations, electrical wiring or plumbing, sealants, insulation, house wrap, and of course siding and drywall. Our testing looks at many combinations of these types of products and has provided manufacturers with valuable information on how their products impact air infiltration. While much of the test data is proprietary to those manufacturers, one thing is abundantly clear – you need to pay careful attention to details when installing all the products in order to get the best result. It is amazing how much air can leak through a small tear or untapped seam in the house wrap or a gap in the caulk at the bottom plate.
The Home Innovation lab stands ready to continue to help product manufacturers and builders find ways to meet the air infiltration requirements of the 2012 IECC.
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