0 Helpful?

Insulating a cathedral ceiling

I live in an early Lindell cedar kit home. I shan't go into the construction method but it is far from conventional. I need to add insulation and also re- roof. I was thinking of stripping the roofing and sheathing, laying down either 2x4 or 2x6 rafters, filling the bays with Thermax insulation, sheathing and re-roofing. My question is if the rafter bay is not completely filled do I absolutely have to vent the bays. I understand that the reflective coating of the Thermax is only effective when used with an air gap, but to vent the roof, because of the original construction method, would be a total pain in the behind. Any and all ideas will be greatly appreciated.
Thanks ....Dave.

Asked by Dave Hodges
Posted Jan 17, 2013 7:27 PM ET
Edited Jan 17, 2013 8:04 PM ET


2 Answers

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

It makes sense to add rigid foam on top of your existing roof sheathing if you are re-roofing. You don't need ventilation channels, as long as you install enough foam. And you don't need 2x4 or 2x6 rafters -- all you need is a thick layer (or two layers) of rigid foam, followed by a layer of plywood on top of the foam.

As an alternative, you can use a product called nailbase. (Google it.)

More information here: How to Build an Insulated Cathedral Ceiling.

Answered by Martin Holladay, GBA Advisor
Posted Jan 17, 2013 7:49 PM ET


I agree to what dave said you can use rigid foam for re-roofing and also the article given is very useful for us to understand how to build insulated cathedral ceiling.

Answered by Greg Pittman
Posted Jan 18, 2013 7:16 AM ET

Other Questions in Energy efficiency and durability

Anyone familiar with Insultex house wrap?

In Green products and materials | Asked by Marcus Sheffer | Jul 31, 15

Double Stud Wall sheathing and vapor barrier

In Plans Review | Asked by Jimmy Nguyen | Sep 30, 15

vapor barrier in attic?

In Energy efficiency and durability | Asked by Lucyna de Barbaro | Oct 4, 15

How is thermal bridging prevented?

In General questions | Asked by S. Schneider | Oct 5, 15

Why does opening the HVAC closet door affect duct blaster number?

In Energy efficiency and durability | Asked by Benjamin Barker | Oct 6, 15
Register for a free account and join the conversation

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