cathedral ceiling

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Old 12-25-10, 01:24 PM
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cathedral ceiling

I have a 20x20 addition with a cathedral ceiling, I noticed that i have a drip in the room, the temp has gone up over freezing today for the first time in a week or so, Oswell .This room has a finished pine ceiling, it has a ridge vent, has the plastic vats tacked to the inside of the roof above the insulation, for an air space, also there were holes drilled into the spaces that were dead ended by skylights. The guy that built it did not cut a long soft vent in , so i bought the 2.5 plastic round ones. It only seems to drip from the side with no sun as the rest appears to be dry. I'm curious , is the ridge vent big enough? should the softs be cut the whole length?? any help will be appreciated
 
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Old 12-25-10, 04:21 PM
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You likely have frost buildup on the bottom of your roof sheathing. It happens primarily on the north facing sides of roofs, since that side does not heat up enough from the sun to melt the frost every day... so it continues to build up. When you get a warm day, the frost melts. This is a pretty common problem with cathedral ceilings in my area. Drilling holes through framing for added ventilation NEVER works well, as 1 sq inch holes just do not move air. You didn't say WHERE the leak was in relation to anything else on the ceiling. Is it near the skylights? About 4' from the peak?

I assume you have drywall above the pine ceiling, and a VB above the drywall?

Still added ventilation is probably the key. That humidity needs to escape or else it will build up as frost. Loose fitting fiberglass can make some areas more frosty than others.

The drips usually occur at the edge of a sheet of sheetrock, so the melting is probably occurring farther up the ceiling and its running downhill until it finds a taped seam.

Adding soffit ventilation will probably help if there are proper vents installed in every rafter bay. But if they are only installed in every 3rd one, for instance, you might be getting frost buildup only in the rafter bays that aren't ventilated as well. Hard telling without taking the soffit off.
 
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Old 12-27-10, 12:29 PM
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I do not have dry wall , but I do have a vapor barrier installed, the pine is T&G. every bay is vented from the roof to the sofit , unless there is a skylight there. I guess I will have to run a new sofit in the spring with it cut out in the middle as I am sure it will flow more air then the 2.5 holes in each bay. also I guess I will chk inot making the ridge vent bigger if possible
 
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Old 12-27-10, 02:31 PM
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If your VB is Kraft faced insulation, it's probably not providing enough moisture resistance, since Kraft facing is a vapor retarder, not a VB. (if kraft facing is stapled to the sides of the rafters there will be even more air leakage) With no drywall to serve as an air barrier (t&g pine is not an air barrier), the wood ceiling is probably allowing some air leakage into the attic. Moisture would obviously follow the air leakage. If there is a poly VB, that would be better, but there could still be air leakage at any overlapping seams.

Hopefully any improvements you make will solve the problem for next year.
 
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