How open should a ridge vent be?
atticusbuilds
| Posted in Energy, Heating & Insulation on
I live in Maryland and I have an attic with gable vents on each end and a ridge vent. I recently installed some soffit vents and have noticed a huge improvement in attic temperature, but noticed that there really is no gap under the ridge vent (maybe a quarter of an inch in places). Shouldn’t I cut an inch or so back from each side of the peak to actually allow hot air to escape? If so, should I block the gables and just have a soffit/ridge combination, or is any ventilation good ventilation.
Thanks.
Replies
Gable vents and Ridge vents do not work together.
other than that....Bump
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It sounds like your "ridge vent" is merely an "architectural element" at present.
If there is no gap, 1/4" = no gap, under the ridge vent ----it is not a vent, just a relatively expensive ridge shingle.
To answer your question - yes, there needs to be a gap in the sheathing, at the ridge, under the vent for it to function properly.
1" to 1-1/4" on each side of the ridge peak is about standard. Manufacturers have their own specs as to width for their product.
>>I recently installed some soffit vents and have noticed a huge improvement in attic temperature,....<<
Given your current configuration, I would guess the current air flow pattern is: cooler air "in" at your new soffit vents and heated air "out" at the gable vents.
This generally produces a dead spot for circulation at the center of the house / ridge line. But, as you said, it is better than it was before!
Closing the gable vents and opening the ridge vent will provide a more uniform air flow pattern. Keep in mind that for a ridge vent to function at it's best, the soffit venting needs to be evenly distributed and balanced with the ridge vent area. I have been taught that a continuos soffit vent and a full length ridge vent will produce the best results.
By "balance" I mean that the free vent area (FVA) of the soffit vent must equal or exceed the FVA of the ridge vent. Air flow will be limited by the lesser FVA.
In other words, you could have a huge FVA on the ridge, but it will not pull any more air than the FVA of the soffit venting will allow. This was exactly your situation when you had gable vents and no soffit vents - you added soffit vents and observed a marked improvement - that happened because you provided a place for the gable vents to draw cooler air "from".
Net Free Vent Area (NFVA) is generally printed on the individual soffit vents and on the packaging for the ridge vent. NFVA is not a simple area calculation, baffling, screening, etc all influence the NFVA. NFVA is always less than the actual area of the venting device.
The object of the game is to be able to pull cooler air from all around the house and let it travel to the ridge vent without dead spots in corners or other areas of the attic.
Sounds like you are on the right track, open up the ridge and maybe add some more soffit vents.
Jim
Edited 6/2/2009 9:24 am ET by JTC1