Attic Ventilation & Baffles

The mistake that follows a cheap insulation job

Blow sixteen inches of insulation into an attic and the material at the edges pushes straight into the eaves, blocking the soffit vents. The attic can no longer breathe. Warm moist air that leaks up from the house has nowhere to go, meets a cold roof deck, and condenses. In an Ontario January it condenses as frost, and in March the frost melts.

That is the origin of most of the attic mould we are called to remove: not a roof leak, an insulation job done without baffles.

What a correct attic looks like

• Baffles in every rafter bay that has a soffit vent below it, holding a clear channel from the soffit to the open attic.
• Intake area at the soffit roughly matching exhaust area at the ridge. Ridge vent with blocked soffits is worse than no ridge vent, because the exhaust pulls its make-up air out of the house.
• Bathroom and kitchen fans ducted through the roof or wall, never dumped into the attic. We find fans venting into insulation on a regular basis.
• An air-sealed, insulated hatch. It is the largest single hole in most ceilings.

When ventilation is the whole job

If your attic is already deep — over R–35 — there is no insulation rebate to chase, and adding more would be money for very little. But if the soffits are blocked and the hatch is bare, the attic is underperforming its own depth. That is a half-day job and we price it as one rather than selling you insulation you do not need.

Common questions