How to Inspect Ridge Vents from the Attic

Guide to Inspecting Attic and Under-Roof Ventilation - what's at the ridge?
- How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage
- How to detect roof venting deficiencies, attic insulation defects, and attic condensation problems
Questions & Answers about attic moisture, condensation & ventilation: check the ridge vent from inside the attic
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Roof venting at the ridge, inspect from attic: this article describes common attic ventilation defects easily observed at the ridge or high point of the roof, as visible from the attic or building interior.

Inspecting the Ridge Vent System from the Attic

this simple sketch shows the optimium attic vent design with inflow at eaves and outflow at ridge

This article describes inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems in buildings. It describes proper roof ventilation placement, amounts, and other details. This discussion is part of "How to Correct Improper or Inadequate Attic or Under-Roof Ventilation in buildings" in our discussion of "Attic Condensation".

You need the gap at the ridge (or "peak") of the roof for the ridge vent to work. Of course some roof shapes such as pyramid or shed roofs merit special techniques to obtain effective intake and exit venting.

But for a simple gable-styled roof structure, here is what a ridge vent looks like from inside the attic of a home.

The ridge vent cut at the roof ridge or peak extends the entire length of the ridge, stopping just a foot or so from either end, and should give 1.5” to 2.5” of open space (no plywood) on either side of the ridge board for attic air to escape out through the ridge vent.

Fake ridge vents: As depicted by the pair of photographs above, sometimes we find that a builder has installed a ridge vent from outside but s/he failed to cut away the roof plywood to provide the exit air path to properly vent the attic. In this case this lazy man's faux ridge vent installed outside should be removed along with any ridge cap shingles below it.

The ridge vent slot should be cut to remove roof sheathing as we described just above (or best, following instructions of the ridge vent manufacturer).

Do not cut into the rafters themselves. Then install the ridge vent again and you'll have a working roof exit vent system.

Roofing Felt Obstructed ridge vents: It’s less common for us to find that a builder cut away plywood for the ridge vent, but that s/he installed building paper or more likely roofing felt over the opening before installing the ridge vent.

In this case just cut away the building paper to expose the underside of the plastic ridge vent mesh, plastic Cor-A-Vent material (looks like a plastic version of the edge of a cardboard box) or the opening into the aluminum ridge vent (depending on which type of ridge vent was installed).

Check that the ridge vent material itself is not blocked by building paper (which you can simply cut away).

Shingle-obstructed ridge vent warning: If when inspecting from the attic and looking up into the slot of removed-plywood at the ridge of the roof you see the under side of a roof shingle, either the roofer made the ridge vent a bit longer than needed, or something else is going on that we’d need to check from outside.

In any case, do not cut away roofing shingles over the ridge vent as you might invite a roof leak.

If your attic or under-roof cavity has a problem with moisture or mold, installing continuous, un-blocked, aggressive exit venting at the ridge is an important step.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Thanks to reader F. Terrell for careful technical editing 06/18/2010
Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com 11/06 & 12/08
John Annunziata, P.E. - NY Metro ASHI during informal chapter discussions about roof and attic ventilation options (1986-1996).
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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