0 Helpful?

How can I fix a poorly ventilated cathedral ceiling insulated with kraft-faced insulation?

I am in the planning stages of renovating a home that has cathedral ceilings with 2 x 8 rafters and R-19 kraft-faced insulation. Ventilation is poor at best. There is frost on the underside of the roof sheathing.

I would like to turn it into a hot roof by sealing up any vents and either replacing the the insulation with closed-cell foam or adding 2 two-inch layers of polyiso on top of the roof deck (leaving the existing insulation in place). If I choose the latter, will I be trapping moisture with the kraft facing?

Asked by Frank Ball
Posted Jan 22, 2013 9:20 PM ET
Edited Jan 23, 2013 2:56 PM ET

Tags:

1 Answer

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.

Frank,
Your proposal to install 4 inches of polyisocyanurate on top of your roof sheathing will work in climate zone 6 or anywhere warmer.

In colder climates (climate zones 7 and 8), the rigid foam needs to be thicker, in order to keep the temperature of the roof sheathing above the dew point during the winter.

The kraft facing on the fiberglass batts is optional. It won't do much to help your roof assembly, nor will its presence cause any problems.

For more information, see How to Build an Insulated Cathedral Ceiling

Answered by Martin Holladay
Posted Jan 23, 2013 6:38 AM ET

Other Questions in Energy efficiency and durability

Insulating Unfinished Basement Ceiling in Flood Plain

In Energy efficiency and durability | Asked by Joseph McGrail | Feb 18, 18

Crawlspace Beam Layout

In Energy efficiency and durability | Asked by alexallo | Feb 16, 18

How exterior air seal at chimney to wall interface? Chimney spalling.

In Energy efficiency and durability | Asked by Mike McLaine | Feb 18, 18

Cold weather performance reports from minisplit owners

In General questions | Asked by Martin Holladay | Jan 2, 18

Recommended gas furnace for 3550 square foot house

In Energy efficiency and durability | Asked by Vissu | Feb 19, 18
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!