Seeing the Building: Inside In the attic Black fg over bypasses shows the house loads of air blown through it. Slight depressions in the surface of the insulation can indicate a huge air intrusion below. Batts are often tented over open stair wells and valences. Extended framing, ballooned framing, and other building discontinuities are likely bypasses. The really big hole leading down the rafters over sloped ceilings are visible from the attic.   Smaller holes such as plumbing and wiring penetrations and recessed lights can be spotted.   Any ductwork found in an attic is a problem. This is a terrible practice and the people who do it have no sense of craftsmanship, much less duct sealing. Large bypasses are often found around chimneys. Back | Next