Glossary · Insulation & windows
Attic bypass
Also called: attic bypasses · attic air leaks
A hidden opening from the living space into the attic, around chimneys, plumbing stacks, wiring, pot lights or wall tops, that leaks warm air.
What it means
Bypasses are often buried under insulation, so warm, moist air flows straight past it into the attic. Typical spots are the attic hatch, the tops of interior and exterior walls, plumbing stacks, chimneys (which need non-combustible fire-stop material), ducts, wiring holes and recessed lights. They're sealed from the attic before more insulation is added.
Why it matters in an audit
Sealing bypasses stops the biggest stack effect leaks, prevents attic frost and mould, and helps prevent ice dams.
In Canada
NRCan notes standard recessed lights are hard to air seal and recommends approved airtight fixtures or covers.