Common attic bypasses are located around chimneys, ceiling light fixtures, heating ducts, kitchen and bath exhaust fans, plumbing, electrical wires, dropped ceilings and soffits.
Bypass Over A Stairway
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!
Furnace Flu Bypass
Also, see attic insulation.