Helpful? 0

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 Tue, 01/22/2013 - 22:20
Edited Wed, 01/23/2013 - 15:56

Tags:

1 Answer

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.
Helpful? 0

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, GBA Advisor
Posted Wed, 01/23/2013 - 07:38

Other Questions in Energy efficiency and durability

Radon mitigation or ERV for old home with dirt wall basement?

In General questions | Asked by Scott Van Der Veer | Oct 30, 14

Foam insulation question for 100-year-old brick home

In Green building techniques | Asked by Wes Leland | Oct 30, 14

Minimum R-values for exterior foam for 2x6 walls

In Energy efficiency and durability | Asked by Craig Steinman | Oct 30, 14

Closed crawlspace with dehumidifier and foundation insulation

In Energy efficiency and durability | Asked by Michael Geoghegan | Oct 27, 14

Roxul comfort board in basement?

In Energy efficiency and durability | Asked by Nyle Phillips | Sep 27, 12
Register for a free account and join the conversation


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