Although building scientists have understood the advantages of airtight construction details for years, few residential plans include air barrier details. That’s nuts.
Do the blueprints show where the air barrier goes?
Ideally, construction documents should show the location of a building’s air barrier, and should explain how the builder is expected to maintain air-barrier continuity at penetrations and important intersections. In a typical house, these intersections might include:
- where the basement slab meets the basement wall;
- where the basement wall meets the mudsill;
- where the mudsill meets the rim joist;
- where the rim joist meets the subfloor;
- where the subfloor meets the bottom plate;
- where the top plate meets the vertical drywall; and
- where the top plate meets the ceiling drywall.
A designer who doesn’t know how to make these areas airtight can hardly fault a builder who fails to intuit details that aren’t even mentioned on the plan. (For more information on air barriers, check out these three resources: Questions and Answers About Air Barriers, the GBA Encyclopedia, and a useful Web page from Oikos, “Advanced Air Sealing.”)
The road ahead is steep
If the day ever comes when most new homes include an air barrier that addresses typical penetrations and the intersections listed above, energy efficiency experts will cheer. That day is a long way off, however.
In the meantime, some progressive builders insist that every home needs not one but two air barriers: an exterior air barrier and an interior air barrier. Although this belt-and-suspenders approach is controversial, it has many strong advocates.
To understand the controversies surrounding double air barriers, it’s important to explain the two positions.
One good air barrier is enough
The basic rule of infiltration is “air out always equals air in.” If you have a good air…