Can you add a ridge vent to an existing roof?
Short answer. Yes. A ridge vent can be added to most existing shingle roofs by removing the ridge cap shingles, cutting a ventilation slot through the decking along the peak, installing the vent, and nailing new cap shingles over it. It only helps if the attic has soffit intake, and other exhaust vents should be closed off once the ridge vent is in.
Questions to answer first
- Is there intake? Look inside the attic at the eaves for daylight or vent openings. If the soffits are solid, plan to add soffit vents or edge intake vents too.
- How long is the ridge? Hip roofs may have too little ridge to provide enough exhaust.
- How old are the shingles? Brittle shingles break when the old cap is pulled, and new cap shingles may not match faded field shingles. On a roof with only a few years left, adding the vent during replacement is usually smarter.
- What other exhaust is there? Gable vents, box vents, and power fans should be closed or removed so they do not short circuit the new ridge vent.
How the retrofit is done
- Remove the existing ridge cap and the nails along the peak.
- Snap lines and cut the slot with a circular saw set to the deck thickness, avoiding the rafters or ridge board. Stop short of the ends and of any chimney or wall, as the vent instructions specify.
- Clear debris and check that insulation or framing does not block the slot from below.
- Install the ridge vent centered over the slot, using the longer nails the manufacturer calls for.
- Install new hip and ridge cap shingles over the vent with the specified exposure and nails.
- Patch any box vents being removed with new decking and shingles woven in.
On most homes this is a job of a few hours, not days. See ridge vent vs box vents and what to expect on roof replacement day.