Top plates of interior and exterior walls are a common point of air leakage. Minimizing air leakage at these locations, especially at the ceiling perimeter, is one of the most effective air-sealing strategies to improve the home's airtightness. If the home has a polyethylene sheet at the ceiling level that is not
detailed as an air barrier, it will allow air leakage at every location where the ceiling finish terminates. In addition, even with a polyethylene air barrier at the ceiling, service penetrations (e.g. electrical, plumbing) in the top plates of interior walls are often overlooked. This air sealing procedure is for top plates without a properly detailed air barrier at the ceiling plane. This procedure is not required if a polyethylene sheet is in place and runs between the two top plates of the wall, though it may still apply to service penetrations.