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TOPIC: Condensation Issues

Vapor Barrier

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I bought the house that somehow slipped through/by many of the building codes. I won't go into my laundry list... In the spring I will have a contractor replace my 7 year old shingles with metal. My concern is this. I have vaulted cielings that are vented from eave to ridge. The cieling in the house is T&G pine then no vapor barrier, then 12" of faced fiberglass, then a foam vent channel, then the roof deck. Absent the vapor barrier could some of my water troubles be water condensing once it makes its way through the fiberglass and hits the cool foam channel/air space? I dread putting on a new roof and then still haveing water problems, but I also can't stand to think about ripping out 750-1000 sq ft of T&G just to put up a sheet of plastic and replace the T&G. Damned if I do damned if I don't?
Guest User

2/24/2006
I would check and make sure that your vented space is really working. Is it continuous? Are the intake vents open and unblocked? Is there a ridge vent? Ideally, I would like to see the vapor barrier in place. If your ventilation is working and you do feel you have condensation problems, then adding the vapor barrier is probably important. Also, look for sources of undue moisture inside the home -- bathroom or dryer vents not directed outside, ventless gas stove, etc.
Todd Miller
Isaiah Industries, Inc.

2/28/2006
I redid the eave vent openings, covers, and sofit on the front and back of the house. I was able to shine a light up into the vent space in the front of the house and did remove some rodent housing in the vent channel. In the back I was unable to do this unless I was willing to remove the ridge cap and look down the channel and not look up. I decided to do this at the time of reroofing to save time and money. Instincts, and experience with this house, told me that since the workmanship and quality of the eave vents was so poor the ridge cap might also be hiding some secrets. Like not a large enough air gap and or the filter material is pounded down to tight to allow air flow. I guess that I will just have to put the new roof on, wait for winter and see what happens.
Guest User

3/6/2006
Good luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

3/8/2006
Hello, saw this old string and notice the problem is similar to my own and wondered if there was anything new on the topic, since this was last used. I'm about an hour west of Seattle, but am experiencing similar issues with a very similar cathedral roofing system. The house is a new construction monitor barn style. Two stories in the center, two side extensions that join the main house half way up the second story. All roofs are cathedral. Metal snap-loc style roofing, felt paper, OSB sheathing, 1" air space, 6" of ridgid foam, forced tight and well sealed, all above the finished ceilings. Some ceilings (kitchen and bath) are drywall, the rest are 6" wide T & G. This is the second year the house has been heated during the winter, but the first with folks living in it, cooking, bathing, creating moisiture, etc. Temps were below freezing for the past few weeks. Heavy morning frost, humidity above 70 percent outside, not much rain, etc, but as soon as the first warm day came we got water dripping randomly out of the T & G pine boards. Mostly on the side facing east. Could be the west side never warmed up enough, since it stays colder and is more protected by trees, and the temps didn't stay warm for long before dropping again.... Wasn't a lot of water, but enough to concern me, since I think it must be interior warm air freezing under the sheathing and then dripping back on the ceiling once warmed. Every rafter bay has full soffit vents at the bottom and and exit venting at the top (ridge and side wall both) according to the roof manufactures instructions. Basically a 1" cut in the OSB sheathing to let the air out and under the flashing. One thing to note is that when the building inspector was told I'd be using a full 6" of ridgid foam, he did not want a plastic vapor barrier between the pine and foam. He was worried it would act as two vapor barriers, trapping air between them. We did tuck tape the seams. Also, this foam was wedged in pretty tight to the rafter bays and beveled to the roof pitch to really fill those rafter bays, leaving just the 1" void for Venting (6" of foam into a 2x8 rafter). Need some advice, short of tearing out the pine ceiling to ad a plastic vapor barrier or sheetrocking over the T & G to act as a better barrier.... Would raising the temp in the house, when the outside temp drops below freezing (usually only a few weeks each winter here), hurt or help the situation? Thanks Brian
Brian Henry

1/5/2011