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Ridge Vent Gap


Mark P
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A 13 years old house has a ridge vent installed however the gap(from inside the attic) under the vent is less then 1/4 - 1/2" wide. There are also soffit vents, but nothing else. There was no damage or signs of moisture in the 1200sf attic. My concern is that the ridge vent gap was not cut large enough, I usually see 1.5 inch+ gaps. What size gaps do you usually see under ridge vents? I think I'm going to recommend adding some roof vents. Thoughts?

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Originally posted by AHIS

A 13 years old house has a ridge vent installed however the gap(from inside the attic) under the vent is less then 1/4 - 1/2" wide. There are also soffit vents, but nothing else. There was no damage or signs of moisture in the 1200sf attic. My concern is that the ridge vent gap was not cut large enough, I usually see 1.5 inch+ gaps. What size gaps do you usually see under ridge vents? I think I'm going to recommend adding some roof vents. Thoughts?

Like you, I usually see about 1-1/2 inches of gap for the ridge vent.

If there were no signs of trouble due to the abnormally small cut-out, I'd just note its presence.

If there were signs of trouble, I'd tell them to cut it out properly. The ridge vent, installed properly will work better than retrofitted roof vents.

- Jim Katen, Oregon

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I see it quite often too. If there are no other high vents, I recommend correction even if there aren't any signs of it causing a problem.

Here's my boilerplate: The sheathing at the ridge vent is not fully cut. This will hamper airflow through the vent. A qualified roofer should cut sufficient openings in the sheathing.

If the attic also has through the roof or gable vents, and there is no mildew, no black marks around the roofing nails and no sap droplets on the framing, I recommend monitoring the attic for signs of poor ventilation.

I know some here claim to never, ever use that weasel word 'monitor', but I don't have a problem using it. There's nothing wrong with saying that something's not right, it's not causing a problem now, but just might in the future, so keep an eye on it.

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I've often wondered myself about the 'correct' installation of a ridge vent. I'm personally not a proponent of ridge venting - I prefer roof jacks and / or a combination of gable end vents.

Its surprising, however, to do a quick calculation of how much ventilation a ridge vent offers. I never include calcs in the inspection report, but just figure some quick numbers for my personal and professional benefit.

Mark, even multiplying that 1/2" wide gap in your attic times the length of the vent might give you a surprising number that would likely satisfy the 'code'.

This of course would all be trumped by the fact that the ridge vent mfg. may require a minimum gap size.

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