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gerald staggs Posted: Feb 25, 2009 02:57 PM	vaulted ceiling insulation i have a room with a vaulted ceiling framed with 2 x 10’s and because of the design, it is unable to be vented. i could place a vent on the ridge, but there would be no way for air to circulate up to the ridge. on the upper side, the roof consists of 1 x 6 decking, 30 lb felt, 1 x 4 horizontal nailers 18”oc, foil/bubble/bubble/foil, and a metal roof. can i spray the underside of the 1 x 6 decking with urathane foam and then insulate between the urathane foam and the sheetrock ceiling with r30 batts without having moisture/condensation problems down the road? i am located in middle tennessee with a pretty humid climate. thanks.
mason Posted: Feb 25, 2009 04:32 PM	In a mixed climate such as Tennessee you should be able to spray 1 inch of closed cell foam and then install your fiberglass batts on top of it without experiencing condensation problems. But to be safe you would want the supplier or contractor to perform hygrothermal modeling such as a WUFI simulation to make sure. This typically runs around $300 if you have an outside consultant (like me) to provide it.
gerald staggs Posted: Feb 26, 2009 12:20 AM	are the batts you are referring to have a paper moisture barrier or not? thanks for the recommentation too!
mason Posted: Feb 27, 2009 01:15 PM	No the fiberglass would not require a vapor retarder so long as the foam thickness is sufficient to prevent condensation. You might need to spray 1.5 inches of foam to meet an R 39 if using R 30 fiberglass.
Posted: Feb 27, 2009 06:33 PM	why not fill the vault with 8-10" open cell as a cost effective alternative,,,this is a good application for this product...will give you plenty of thermal performance,,very adaptable to the transitions from flats to vault,,,
Posted: Mar 06, 2009 01:34 PM	Gee Foamdude, There you go making sense again, cut that out.

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Comments

gerald staggs

Posted: Feb 25, 2009 02:57 PM

vaulted ceiling insulation

i have a room with a vaulted ceiling framed with 2 x 10’s and because of the design, it is unable to be vented. i could place a vent on the ridge, but there would be no way for air to circulate up to the ridge.

on the upper side, the roof consists of 1 x 6 decking, 30 lb felt, 1 x 4 horizontal nailers 18”oc, foil/bubble/bubble/foil, and a metal roof.

can i spray the underside of the 1 x 6 decking with urathane foam and then insulate between the urathane foam and the sheetrock ceiling with r30 batts without having moisture/condensation problems down the road? i am located in middle tennessee with a pretty humid climate. thanks.

mason

Posted: Feb 25, 2009 04:32 PM

In a mixed climate such as Tennessee you should be able to spray 1 inch of closed cell foam and then install your fiberglass batts on top of it without experiencing condensation problems.

But to be safe you would want the supplier or contractor to perform hygrothermal modeling such as a WUFI simulation to make sure.

This typically runs around $300 if you have an outside consultant (like me) to provide it.

gerald staggs

Posted: Feb 26, 2009 12:20 AM

are the batts you are referring to have a paper moisture barrier or not? thanks for the recommentation too!

mason

Posted: Feb 27, 2009 01:15 PM

No the fiberglass would not require a vapor retarder so long as the foam thickness is sufficient to prevent condensation. You might need to spray 1.5 inches of foam to meet an R 39 if using R 30 fiberglass.

Posted: Feb 27, 2009 06:33 PM

why not fill the vault with 8-10" open cell as a cost effective alternative,,,this is a good application for this product...will give you plenty of thermal performance,,very adaptable to the transitions from flats to vault,,,

Posted: Mar 06, 2009 01:34 PM

Gee Foamdude,
There you go making sense again, cut that out.

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