How to Install a Roof Ridge Vent

Before you start — check the intake

This is the step people skip and it is the reason most ridge vents disappoint. Go into the attic with a torch and look along the eaves. If insulation has been pushed into the eave and closed off the soffit vents, the ridge vent will have nothing to draw from and the attic will stay hot. Fit baffles in each rafter bay to hold the insulation back and restore the path first.

Intake area should at least match exhaust area. More exhaust than intake makes a ridge vent draw air in at one end and out at the other, or pull conditioned air up out of the house through ceiling gaps.

Cutting the slot

• Snap a chalk line each side of the ridge, typically 1 inch out from the centre for a 2-inch total slot — read the vent instructions, as products differ.
• Stop the slot 6 inches short of each end of the ridge, and short of any hip or chimney.
• Set the circular saw depth to the thickness of the sheathing only, so you do not cut the ridge board.
• Remove the existing ridge cap shingles first, and pull the nails rather than cutting over them.
• Clear the offcut and any debris out of the attic before you close it up.

Fitting the vent

• Roll or rigid sections centre over the slot and are nailed through the marked fastening points with nails long enough to reach through the sheathing.
• Butt sections tight to each other and use the end plugs supplied, so wind-driven rain and insects cannot enter at the joints.
• Cap over the vent with hip and ridge shingles, following the exposure the vent manufacturer specifies rather than the shingle default.
• Only the final cap takes an exposed fastener, sealed with roofing cement.

Common mistakes

• Leaving the old box vents or a powered fan in place on the same plane. They short-circuit the ridge vent, which then becomes an intake.
• Cutting the slot the full length of the ridge, so the end plugs cannot seal.
• Cutting through the ridge board because the saw depth was set to the shingle thickness rather than the deck.
• Using cut three-tab as cap over a vent in cold weather, where the sharper bend over the raised vent cracks it.

Frequently asked questions

How wide should the ridge vent slot be?

Commonly 2 inches total, cut as 1 inch each side of the ridge centre, but follow the vent manufacturer instructions — products differ and the slot width is what their net free area rating assumes.

Can I install a ridge vent without soffit vents?

You can fit it, but it will not work. A ridge vent is exhaust and it needs matching intake at the eaves to draw from. Without soffit intake it either does nothing or pulls conditioned air up out of the house.

Should I remove old box vents when adding a ridge vent?

Yes, on the same roof plane. Leaving them in short-circuits the system — the ridge vent starts drawing air in through the nearest box vent instead of up from the soffits.

How far from the end of the ridge should the slot stop?

About 6 inches at each end, and short of any hip, chimney or wall. That leaves solid deck for the end plugs to seal against so wind-driven rain cannot enter at the ends.