Dont skip air sealing

Bypasses are hidden air passageways that lead from the heated space into the attic. Because warm air rises, it continuously moves up the bypasses and escapes into the attic.

Common attic bypasses are located around chimneys, ceiling light fixtures, heating ducts, kitchen and bath exhaust fans, plumbing, electrical wires, dropped ceilings and soffits.

In addition to being a source of heat loss, bypasses also cause indoor moisture problems. Warm air leaking into the attic causes moisture to condense onto cool surfaces.

This moisture can rot wood joists and reduce the effectiveness of your insulation. Moisture problems can become so bad it can even "rain" in your attic!

Bypasses are also the primary cause of ice dams and attic frost.

Also, see attic insulation.