How do you properly vent a roof during a roof replacement?
Short answer. To properly vent a roof during a replacement, the roofer sizes the system from the attic floor area, removes old or mismatched exhaust, cuts a ridge slot to the vent maker's specifications, adds intake where the soffits fall short, and installs everything to the shingle manufacturer's requirements. Done right, the attic ends up with balanced intake and one type of exhaust.
The roofer's sequence
- Assess: measure the attic footprint, inventory existing vents, check soffit intake from inside the attic, and note any bath or dryer exhaust ending in the attic.
- Design: choose one exhaust type, usually a ridge vent on gable roofs or box or hip vents on hip roofs, and calculate the net free area needed.
- Tear off: remove old shingles, vents, and turbines. Holes from vents being eliminated get new decking.
- Cut the ridge: snap lines and cut the slot to the vent's specified width, stopping short of the ends and of chimneys and walls.
- Add intake if needed: on homes without enough soffit venting, intake vents can be installed at the roof edge under the first courses.
- Underlayment and shingles: install up to the slot without covering it.
- Install exhaust: set the ridge vent with its specified nails, or flash box vents into the shingle courses.
- Cap: install hip and ridge cap shingles over the vent.
- Close extras: block gable vents from inside if the new ridge and soffit system replaces them.
Mistakes that undo good venting
- Installing a ridge vent on an attic with no intake.
- Leaving an old power fan or box vents in place next to a new ridge vent.
- Cutting the slot too narrow, or forgetting to cut it at all under the vent.
- Short nails that let cap shingles and the vent blow off.
- Covering the slot with underlayment.
Questions to ask your roofer
Ask how they calculated the vent area, which exhaust type they will use, how they will handle intake, and whether the plan meets the shingle manufacturer's ventilation requirements. See what to expect on roof replacement day and roof ventilation basics.