How to Inspect Ridge Vents from the Attic
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Guide to Inspecting Attic and Under-Roof Ventilation - soffit intake
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
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Here we discuss attic ventilation defects at the ridge or high point of the roof, as visible from the attic or building interior. This forms part of "How to Correct Improper or Inadequate Attic or Under-Roof Ventilation in Buildings", part of our discussion of "Attic Condensation".
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.
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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Alan Carson Carson Dunlop Associates, Toronto, Ontario. Mr. Carson is a home inspection professional, educator, researcher, writer, and a principal of Carson Dunlop Associates, a Toronto home inspection and education firm. Mr. Carson is a past president of ASHI, the American Society of Home Inspectors
Some great illustrations of the proper under-roof ventilation pathways are offered by Carson Dunlop.
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).
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Thanks to reader F. Terrell for careful technical editing 01/28/2010
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More Information on Building Diagnostic Inspections and Repairs
More Reading about Dealing with Attic Mold, Identifying, Removing, and Preventing Mold in Attics
Be sure to review HOW TO FIND MOLD: How to Inspect Homes and Other Buildings for Mold - the Basics of How to Find Problem Mold Indoors
in our Mold Action Guide. Here are other articles that will be helpful in evaluating attic mold presence, causes, and cures:
How to Clean Moldy Wood Framing & Sheathing How to clean/seal mold from/on exposed lumber or plywood subfloor or roof sheathing indoors - some suggestions based on our field and laboratory research
Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.
InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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