Timber Framers Guild Forums Tools Timberframe Design Timber Frame Roof Insulation

In a cathedral roof ceiling, with rafters or purlins or both visible and decking of some sort on top of those, how does one handle insulation? I found one example in the Fine Homebuilding compilation "Timber-Frame Houses". On page 94 there is a roof cross section that shows a 6x15 principal rafter, with sheathing on top of that, then 2x10s with fiberglass battens between, then more sheathing then shingles. Is this pretty standard? I was thinking of something similar except with blown-in cellulose insulation between the 2x10s instead of fiberglass battens. Code here requires R-30 which comes out to about 9" of cellulose. I'd be interested to hear how others have handled insulation - especially blown-in cellulose - in cathedral roof situations.

Miles

Wrap and strap in place of stress skins. To build an additional structure on top of an already existing structure is redundant. 4" of foam will just about do it, but why stop there? Go for 6" and there is no thermal bridging.

Tim

for some applications I'm a fan of SIPs on roofs. large simple spaces that you can cover quickly. let the TF remain below with TG sheathing pre-applied to the frame, set on the SIPs and detail for the type of roof surface you want. depending on lateral load requirements you may be able to get curtainwall panels (OSB only on 1 side) to do the job...


or following tim's lead on not having 2 structures - simplify the timber frame to work with a conventional built roof. use principle purlins, ridge, and plates to hold up 2x rafters (or even TJIs, etc.) at the depth you need for insulation. use a spacer between the timber and the conventional framing, over frame and sheath the outside (add a hi-r or similar if applicable to limit thermal bridging), blow full of foam or cellulose from the inside, then attach interior finishes from below... lets the timber do the work. and combines conventional framing into a logical way to hold up the roof and insulation. but if you want to save $$ and redundancy you will probably leave out common rafters or common purlins, although I've seen it done either way.

good read:
http://www.arlingtontimberframes.com/enclosure.htm