While it’s important to seal as many air leakage sites as possible, you don’t want to waste time and materials on places that don’t leak. Each project offers unique situations, but here is a list of common temptations that you should avoid.

• On the top floor, corners where walls meet ceilings. That corner is covered with drywall tape and joint compound, so it doesn't leak to the outside.
• Bottom plates of interior walls.
• Corners where outside walls meet.
• Holes for wiring and plumbing in the studs of outside walls. This also applies to joists in outside ceilings and floors.
• Penetrations in the first floor ceiling in a two story house. A well-sealed rim joist makes this unnecessary.
• Penetrations in the first floor above a heated basement. Of course, you might choose to seal these penetrations if you suspect a potential radon gas problem.