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   Guest_ | May 12, 2000 04:52am | #7

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   Can anyone out there tell me if a vapor barrier is required on a cathedral ceiling. The rafters will be furred down to 9 1/4, and there is clearance for insulation and styrofoam baffles to ventilate the under side of the roof deck. Is this considered a ventilated ceiling? I do mainly interior trim but am doing an attic finishing job for a good friend. This job is testing my code book knowledge. Any help on this subject would be kindly appreciated....

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   Guest_ | May 07, 2000 04:32am | #1

   *Dear Doc;It's hard to say what you need to do in your area. In MMMMMinnnnesota where it gggets ppppplenty ccccold the answer is boy howdy do we need a vapor bbbbarrier. If I had a nickel for every cathedral ceiling that had "rain coming in" on it I'd buy a new worm drive. You are right in allowing a one inch unobstructed air space up to a continuous vented ridge. Make sure your insul blanket is high density and use atleast a 4 to 6 mil vapor barrier and tape any holes in the plastic with tyvec type tape. Where you are however I don't know how much condensation problems and ice damn situations you see. I just fixed one last winter where the homeowner called me crying because the condensation was following her vapor barrier down to the wall and than ran behind the drywall and leaked between the window jamb and casings. The previous owner never had a problem because he never spent the winter there. The first problem was unprotected ceiling cans leaking warm air into the attic from the kitchen and bath area. The second problem was no fart fans in the bathroom. The third problem was inadequate insulation at the bottom of the ceiling at the plate line and the real winner was an unvented valley that was dripping wet and to make matters worse the soffit vents were clogged with dirt. Bottom line is you can't be to careful when it comes to cathedrals.You might want to check FHB a few months back, great article on cellulose and vaults.

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   Guest_ | May 07, 2000 05:14am | #2

   *Thanks for your input Don... I am in Raleigh , NC where it doesn't get quite as cold as your area, actually, not near as cold. Our summers are plenty hotter though....

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   Guest_ | May 07, 2000 01:50pm | #3

   *Don,"unvented valley"? Did you mean attic?

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   Guest_ | May 07, 2000 02:53pm | #4

   *In the February JLC and a followup letter to the editor in the May JLC Joe Lstiburek explains why he would not recommend a vapor barrier in your situation. It's a fairly comprehnsive discussion but two conclusions are you do need an effective air barrier and a vapor barrier is likely to cause more problems than it solves.

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   Guest_ | May 07, 2000 03:34pm | #5

   *Red Dog; I meant valley. The old owner put on an extensive addition and hired his neighbor to frame it, a retire engineer, you know the type. He built a lay-on valley and didn't cut in ventilation between the two attic spaces and had no static vents or ridge venting. When we took off the static vents on the cathedral side the old gable truss that divided the new from the old was dripping wet with melted frost. And Bill is right when we lived in Az. we never used any vapor barrier but there was little humidity and temperatures never stayed below freezing for more than a couple of hours.

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   mad_matt | May 12, 2000 04:48am | #6

   *I worked on a house that my dad and I were building for a guy who owned a fairly large hvac business.He wanted to put vapor barriers everywhere. The only problem is that in central Il, the practice then, was no barriers in the ceilings. He argued with insulation reps, plasterers, board hangers, and gypsum reps. they all said no way. His argument was that if your insulation was tight, there would be no condensation, because the air on each side of the barrier would be the same temperature. I believed him over all the reps that were trying to protect their own interests, so when I built my house (with a cathedral ceiling) I used a vapor barrier. 5 years and no sweat. Pardon the pun.