Answers · Is something wrong?
How much attic ventilation does a roof need?
The short answer
It needs balanced intake at the soffits and exhaust at or near the ridge, roughly matched in area, so air enters low and leaves high. Total vent area is set by code as a ratio to attic floor area, and the common failure is not too little area but all of it in the wrong place.
Why balance matters more than total
A ridge vent with blocked or absent soffit intake cannot pull air through the attic; it pulls it from the path of least resistance, which is often the conditioned space below through gaps and recessed lights. That makes the house harder to heat and cool and delivers moisture to the deck. Adding more exhaust to an attic with no intake makes it worse, not better.
What goes wrong in practice
- Insulation stuffed into the eaves, blocking the soffit vents. Baffles exist to prevent this and are frequently missing.
- Soffit panels installed solid rather than vented, or painted over.
- Mixed exhaust types — a ridge vent and powered fans and gable vents together — which short-circuit each other so air enters at one vent and leaves at another without crossing the attic.
- Bathroom and kitchen fans discharging into the attic rather than outside.
Also asked
- Are powered attic fans a good idea?
- They are contested. In a house with air leaks between the living space and the attic, a powered fan can pull conditioned air out of the house, which costs more than it saves. Air sealing and balanced passive ventilation is the approach most building science favours, and it has no running cost.
General information about roofs and about hiring, not advice about your building. Roofing contractor licensing, permits, insurance practice and deductible rules are set state by state and province by province across the United States and Canada, so your own authority is the current answer.