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Karen2e 08-30-2012 10:38 AM

Ridge vent VS Box vent
I live in Tampa, Florida, on a lake with little shade. It's very hot and miserably humid!
I recently had my roof replaced and the roofer sealed the existing ridge vent and installed 3 box vents.

The roofer didn't tell me that he planned to change the venting system. In defending the change, the contractor said that ridge vents leak and that box vents are bigger so there's greater air flow.

The attic is 2100 sq feet. I have soffit vents spaced every 4 feet. I also have radiant barrier insulation that is stapled to the underside of the rafters. When the radiant barrier was installed they left the ridge uncovered but the rest is sealed. The box vents were cut into the roof where the radiant barrier is sealing the rafters which obviously hampers any air flow.

I have a few questions. Are box vents really better? If so, are 3, 4 ft x 20 inches vents enough for a 2100 sq foot attic?

If I leave the box vents, I would have to cut the radiant barrier that's covering the vents. Does anyone know how that effects the effectiveness of the radiant barrier?

Should I install a ridge vent and leave the box vents or should I install a ridge vent and get rid of the box vents?
I really appreciate any advice. Thanks!

Windows on Wash 08-31-2012 09:57 AM

Your roofer is incorrect in both his statement and his applications.

Ridge vents (if a quality rigid unit is used) are not any more prone to leakage and are the most effective ventilation methodology when combined with full perimeter soffits.

The box vents should pick up attic air and should not be behind the radiant barrier.

I am guessing that the soffits are not covered by the radiant barrier and that the radiant barrier is open at the top to vent through the previously installed ridge vent?

Without looking at the roof I cannot comment for certain, however, it sounds like the ridge vent was the more proper ventilation source.

Karen2e 08-31-2012 10:52 AM

Thanks! If I put in a new ridge vent, would you remove the box vents or leave them for extra ventilation? If I leave them, I'd cut the radiant barrier that's covering them. I've read that the ideal system would be the same square footage of venting at the soffit as on the roof. I don't know how important that ratio is. I really appreciate your advice.

joecaption 08-31-2012 12:50 PM

The box vents need to go if you change back to ridge vents.
Did they ever leak before? Was there sheathing damage at the peak of the roof that would make him thing they had been leaking?

If not then he is wrong in makng the change without talking to you first.

Gary in WA 09-01-2012 10:47 PM

You need a ridge vent with baffles;

The radiant should not be cut to lose its purpose.The box vents should be closed off as they are venting just that rafter bay (IF the ridge vent is sized for the attic to handle it alone);

The soffits may be under-sized for the attic as well. At 1/300 = 7 sq.ft. with 3-1/2 at ridge and 3-1/2 at soffits. That would be 9 x 4' = 36 sq.inches at every vent or a 16" x 6" soffit vent grill (existing). Best would be continuous venting. Pictures from the attic of the soffits; the soffit vents from outside, and the box vents from the attic...

How to post a photo or re-size them:


Karen2e 09-02-2012 09:25 AM

6 Attachment(s)
Thanks for all the input. I've attached photos so you can get an idea of the layout. Please excuse the mess, we're in the process of a complete renovation. I'd love your advice on a vent for the new porch. I would think there should be a ridge vent on that too.

I took a picture of the box vents from inside the attic but they are literally covered by the radiant barrier so you can't see them. They span two rafters. There are 2 installed and the roofer planned to install a third on the new porch but I told him to stop.

I didn't think about the soffit vents but you're right, I probably don't have enough. When I looked at them I realized there's paint covering a lot of the holes. At a minimum, I'll buy new ones.
It also never dawned on me that they could be covered with insulation. I'll check that out too. Thanks Again!

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