How to Install a Ridge Vent: Cutting the Slot, Nailing and Capping
A continuous exhaust along the peak. The slot size, where it stops, and the nail length decide whether it works.
- Advanced
- 3 to 6 hours
- Updated
The short answer
To install a shingle-over ridge vent, cut a slot along the ridge through the deck, commonly 1 to 2 inches wide on each side of the ridge board, and stop about 12 inches short of each end. Centre the vent over the slot, nail it with longer nails that reach the framing, then cover it with ridge cap shingles. Choose a baffled vent so wind and rain do not blow in.
A ridge vent is the most even exhaust a roof can have. It runs along the whole peak, so hot, damp air leaves right where it collects, with no holes through the roof face and no vents showing from the street. Fitted with soffit intake, it gives the stack-effect airflow described in how attic ventilation works.
It only works if the details are right. The slot has to be cut to the correct width and stop short of the ends. The vent has to be fastened with nails long enough to reach the framing. And the ridge vent has to be chosen with a baffle, so wind-driven rain does not blow in. On this page, we go through the common shingle-over type.
Before you buy, calculate how many feet of vent you need, see how to calculate attic ventilation. Ridge vents only work with open intake, see how to add soffit intake vents. The vent manufacturer's installation instructions govern for slot width and fasteners. On a metal roof the vented ridge is built from vented closures under the cap, see how to install metal ridge and hip cap.
Tools
- Circular saw with a depth-set blade
- Reciprocating saw or oscillating multi-tool
- Chalk line
- Tape measure
- Roofing hammer or coil nailer
- Hook blade utility knife
- Tin snips
- Shop vacuum
Materials
- Shingle-over ridge vent with a baffle or external baffle, sized by net free area
- Ridge cap shingles
- Roofing nails long enough to go through the vent and the deck, commonly 1-3/4 to 2-1/2 inches, as the vent manufacturer specifies
- Plastic cement where the manufacturer calls for it
- Plywood or fascia scrap for end closures, if needed
Safety first
- Work tied off. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury, and ridges are narrow and exposed.
- Set the saw blade depth to cut the sheathing only, and do not cut into the rafters or ridge board. A saw kickback on a steep roof is dangerous.
- Dust and debris from the slot fall into the attic. Protect yourself and anything below with a dust mask and eye protection.
Step by Step
Step 1: Confirm the attic has intake and open airflow
A ridge vent with blocked or missing intake will pull air from the house. Look in the attic from the eave up. If the soffits are solid, plugged with insulation or painted over, deal with that first. See how to install insulation baffles.
Check for other exhaust vents on the roof. Ridge vents should not be combined with box vents, turbines or power vents on the same roof. See why you should not mix roof exhaust vents.
Step 2: Check the ridge length against the vent you need
The vent should stop short of the ends of the ridge, commonly about 12 inches, so the last stretch is solid. Subtract that from the ridge length to find the usable vent length. If it is less than you calculated, pick a product with a higher net free area per foot or see the options in how to calculate attic ventilation.
On a hip roof, each hip ridge can be vented but short ridges may not provide enough. Do not vent all the way to the end of every hip.
Step 3: Mark and cut the ridge slot
Follow the vent manufacturer's slot width. A common arrangement is a slot about 1 to 2 inches wide on each side of the ridge centreline, leaving the ridge board between. Some roofs have no ridge board, only a rafter peak, and slot widths then differ. Check the instructions.
Snap chalk lines, set the saw depth to just the thickness of the sheathing, and cut both lines. Stop about 12 inches from each end of the ridge or where the instructions say. Finish the ends with an oscillating tool or reciprocating saw, and pull out the cut strips.
Watch out: Cutting too deep into the rafters or ridge board weakens the roof. Set the blade depth to the sheathing thickness and test on scrap.
Step 4: Clean up the opening and check the underlayment
Debris in the slot can block the vent. Remove it from the ridge and from the attic side if it can be reached. Trim the roofing underlayment back from the slot edge if it covers any part of the opening.
Check that shingle courses on both sides come right to the slot, and that the shingle edges are firmly nailed.
Step 5: Set the ridge vent over the slot
Centre the vent on the ridge. The vent's baffle or filter side faces out. Make sure it sits flat on the shingles on both sides, with no ridge that would lift it.
Use the end plugs or closures the manufacturer supplies, or cut and fit an end cap, so that the vent stops where the slot stops. Some vents are rigid sections that butt and connect. Others are a roll cut to length.
Step 6: Nail the vent with the correct nails
Nail length matters. Nails that are too short pop out, and the vent lifts in wind. Many shingle-over vents call for nails around 1-3/4 to 2-1/2 inches long, but check the instructions.
Nail only in the marked nailing zones, never through the vent's open area. Keep the nail heads flush, not overdriven and not standing proud, and use a hand nailer or a coil nailer set to the right depth. See how to use a roofing coil nailer.
Step 7: Cap the vent with ridge shingles
Use cap shingles that match the roof. They should lie over the vent with the exposed part facing away from the prevailing wind. Nail at the positions shown on the vent, through the cap, the vent and into the deck.
The cap shingles hide the vent and shed rain. Cold weather makes shingles brittle, so warm them or cut them with care. See how to install hip and ridge cap.
Step 8: Check the ends and look for air movement
The vent ends should be covered and the ridge cap should seal them off. Do not seal the slot or the vent openings. Look in the attic for daylight or a light breeze at the slot.
On a windy day, hold a hand up to the ridge to feel for airflow. Also check the intake. The ridge vent works only if air comes in at the eaves.
Baffled Versus Unbaffled Vents
A good ridge vent has a baffle, either built into the vent or an external baffle that extends over the top edge. The baffle turns wind over the vent and creates a low pressure zone that pulls air out, and also keeps wind-driven rain and snow from blowing in. Unbaffled, simple mesh vents can let rain and snow in when wind blows across the ridge, which matters for the heavy snow at Hope and wet storms off the Fraser.
Choose a product with a published net free area and a baffle, and check that the product is rated for shingle-over use.
Ridge Vents and Other Exhaust
A ridge vent is meant to be the only exhaust. Mixed with box vents, turbines or power vents, air can be drawn in through the lower vent and out of the ridge without ever crossing the lower attic. The details are in why you should not mix roof exhaust vents. When adding a ridge vent, remove or seal the old exhaust vents.
Common Mistakes
- Cutting the slot through the ridge board or rafters. The roof is weakened.
- Running the slot right to the ends. Wind blows rain in and the ends of the vent look unfinished.
- Using nails that are too short. The vent lifts, and nails back out.
- Choosing an unbaffled vent in a stormy area. Rain and snow are blown in.
- Leaving old box vents or turbines in place. The airflow short circuits.
- Adding a ridge vent with no intake. It pulls air from the house.
When to Call a Professional
If the roof is steep, high or has a complicated ridge, or the slot requires cutting near framing you cannot see, hire a roofer. Cutting a slot is easy to get wrong and hard to undo.
A roofer can also check the whole ventilation system, because a new ridge vent is only part of it.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Replacement service or the towns we cover.
How to Install a Ridge Vent: Questions
How wide should a ridge vent slot be?
It depends on the product, so follow the manufacturer's instructions. A common arrangement is a slot about 1 to 2 inches wide on each side of the ridge centreline, cut through the sheathing only. Some vents specify different widths, and a roof without a ridge board is cut differently, so always confirm.
Should a ridge vent run the full length of the ridge?
No. Stop the slot and the vent about 12 inches from each end, or as the manufacturer specifies. The solid ends keep wind-driven rain out and give the ridge cap something to seal against. Count only the vented length when checking whether you have enough net free area.
What length of nail do you use for a ridge vent?
Longer than standard roofing nails, because they have to go through the ridge cap, the vent and into the deck. Many manufacturers call for around 1-3/4 to 2-1/2 inches, but the vent instructions decide. Short nails back out and the vent lifts in wind.
Do ridge vents let rain in?
A well designed baffled ridge vent installed with the correct slot and nails sheds rain. Unbaffled vents, slots that are too wide or run to the ends, and vents mixed with other exhaust can allow rain and snow in during wind. Choosing a baffled product and following the instructions prevents most problems.
Related Guides
All Ventilation and Attics guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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