Venting A Vaulted Ceiling???

 
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Old 06-16-2008, 04:14 PM   #1
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Venting A Vaulted Ceiling???


I am about to finish an attic and I need to know if I sould vent the vaulted ceiling or not. The rafters are 2x8 and I plan to add an additional two inches so I have room for the insulation. That will give me about 9" for insulation and venting? The homeowner wants the best insulation available but not foam? Any advice greatly appreciated!! They want R-38 but I cant find anything that will fit the space... Should I go R-30 and install baffles to vent behind the insulation? If I do that it will still be real tight with the insulation and the baffle? I want to do this right so there are no moisture problems and acheive a comfortable room as well. All help greatly appreciated
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Old 06-16-2008, 04:20 PM   #2
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Re: Venting A Vaulted Ceiling???


r-30 and the baffles will be a good system, just make sure soffit and ridge have venting. the other thing you can offer them , just before the sheetrock install 1/2'' rigid ins board, 4x8 sheets, tape seams, this will add another r-6 or better on top of your r-30. sheetrock with 1 3/4'' screws.

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Old 06-16-2008, 04:47 PM   #3
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Re: Venting A Vaulted Ceiling???


I agree, but if the are willing to do that, talk them into the spray in insulation.
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Old 06-16-2008, 05:22 PM   #4
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Re: Venting A Vaulted Ceiling???


thanks for the tip Gene, installing rigid foam board never occurred to me. Guess w/ the taped seams it would act as a moisture barrier too-is that good or bad? Would the baffles be absolutally necessary in that case, to move the moisture up and out?
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Old 06-16-2008, 05:34 PM   #5
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Re: Venting A Vaulted Ceiling???


Thanks alot guys, very helpfull. Are there any new high density insulations where I can obtain an R-38 value within a 9" space? The customer doesnt want foam because they are worried about any chemicals that may gas out..
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Old 06-16-2008, 06:05 PM   #6
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Re: Venting A Vaulted Ceiling???


Quote:
Originally Posted by 72chevy4x4 View Post
thanks for the tip Gene, installing rigid foam board never occurred to me. Guess w/ the taped seams it would act as a moisture barrier too-is that good or bad? Would the baffles be absolutally necessary in that case, to move the moisture up and out?
you are correct, tape would act as moisture barrier, therefore unfaced r-30 or score the kraft before installing 1/2'' rigid. baffles are still recomended
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Old 06-16-2008, 08:00 PM   #7
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Re: Venting A Vaulted Ceiling???


Quote:
Originally Posted by gene
baffles are still recommended
Yep, and dont forget what he said earlier too... Make sure the soffit and ridge have venting... Roofers love to talk homeowners into the ridge vent without confirming the existence of soffit vents... At least around here anyway
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Old 06-25-2008, 04:21 PM   #8
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Re: Venting A Vaulted Ceiling???


Quote:
Originally Posted by greg9706 View Post
Thanks alot guys, very helpfull. Are there any new high density insulations where I can obtain an R-38 value within a 9" space? The customer doesnt want foam because they are worried about any chemicals that may gas out..
You just need to sell them the "right" foam. There are foams made of soybean oil that are considered green both due to their origins and their low off-gassing properties....

http://www.biobased.net/
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Old 08-22-2008, 03:37 PM   #9
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Re: Venting A Vaulted Ceiling???


I agree that using the "Green Foam " with sturdy vent baffles laid from soffit to ridge on every joist with continuous soffit ventilation keeps the house warm and the roof cold in Michigan winters. I have a number of clients that report low heat bills and good house comfort with foam insulation.
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Old 08-23-2008, 08:31 AM   #10
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Re: Venting A Vaulted Ceiling???


We did a job just 4 months ago with the same problem and we used a Radiant Barrier which breaths with 3/4 strapping. It rated at a R14.4. It's 97% reflective so it works for heating and coolin.
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Old 08-23-2008, 10:26 AM   #11
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Re: Venting A Vaulted Ceiling???


Quote:
Originally Posted by greg9706 View Post
Thanks alot guys, very helpfull. Are there any new high density insulations where I can obtain an R-38 value within a 9" space? The customer doesnt want foam because they are worried about any chemicals that may gas out..
Do your homework and get the technical info that explains how off gassing has been addressed in the industry. We do 90% foam cathedral ceilings. The other 10% we do with 9" high density and 2" Celotex.

Closed cell spray foam is not the same as the banned formaldehyde from the 80's.
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Old 08-23-2008, 01:37 PM   #12
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Re: Venting A Vaulted Ceiling???


A friend of mine from another forum has a product on the market and can be contacted at; www.soythane.com

His name is Tom Hay and he has been in the industry for 40 + years and has written the standards for Florida code approvals and was involved in the testing of the dome in New Orleans after Katrina.

A very knowledgeable resource if you want to learn about the properties of the materials.

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Old 08-27-2008, 08:35 PM   #13
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Re: Venting A Vaulted Ceiling???


Just a thought here. If I remember right and maybe an insulation guy would correct me if I am wrong. That insulation works best when it expands and fills the bay. The air caught in the fibers is the real insulator. If you cramed a r 21 into a 2x4 bay you would not get a r21 and possibly less than r15 due to the fact that there is less air. Now here is the contradictory part. If you fill a bay in a vaulted ceiling, no vent is required. Only the air space that exist at the peak if any needs venting. The only way to do that are gable vents for intake and ridge for exhaust. This all per code here in southern Oregon.
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Old 09-08-2008, 09:20 AM   #14
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Re: Venting A Vaulted Ceiling???


Insulate with unfaced glass and install a 6 mill vapor barrier with a joist space lap on joints and down the walls 6" or so,tape joints be sure there are no holes. done a few like this and no problems, the first one was in 1975.

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