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Insulation for new construction timber frame with 6-3/4″ wall thickness

nugget247 | Posted in General Questions on

Hi All,

First post here, been lurking on and off for years so first thank you for all the info that has gotten me to this point.

Where I’m at now:  in the midst of building a timber frame cabin/house in the northern half of NH (zone 6).  Exterior framing is rough 6″ timber (true 6″) with 6×6″ for posts and 2×6″ for all other framing members (girts, angle braces, window and door framing etc.).  We’ve sliced and diced 3/4″ EPS panels into 2″ and 6″ wide strips and placed them on the exterior of all framing members (only directly on framing members), taped the seams, and then Tyvek around that.  The siding/sheeting are one in the same, 1×12″ vertical pine boards and will eventually get battens and paint once it all has a chance to normalize moisture wise.  These choices are fixed and I will be dried in by next week.

My current decision/conundrum:  this assembly leaves me with a 6-3/4″ wall cavity which is of course not standard.  I can obviously get it spray foamed 3-1/2 or 4″ thick and call it a day.  Or I can flash and batt with 2″ of spray foam and compress R-19 fiberglass into the remainder of the cavity.  I suppose I could also compress R-30 or R-25 fiberglass into the whole cavity, but I would be concerned about air leaks and performance.  I would feel better about Rockwool in terms of air movement, but it’s not available in this exact cavity depth – 2 layers of R-15 would be 7″ or 1 layer of R-30 would be 7-1/4″ which is close but can I correctly install a vapor retarder over that on the interior?  I’ve never worked with Rockwool but understand that it does not compress at all?

Somebody on this site turned me on to wet spray cellulose in an older post and that sounded great to me, but I can’t find an installer locally.

Our town does not have a building inspector and NH is lax about such things, but I still want to meet modern code whenever possible.

Any other thoughts or considerations I’m missing?  Thank you!

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Replies

  1. Kyle Bentley | | #1

    The rockwool comfortbatt will easily compress that 1/4 inch you're missing. The comfortboard that you may be counfounding it with, is much more rigid.

    If that route isn't an option, there's always blown in fiberglas.

    Edit: I was looking at the OC next gen fiberglass data sheet for other reasons, but i just happen to notice that it comes in 6 3/4" thicknesses! It would probably need to be a special order, but it looks like it's a valid solution to your thickness issue.

    https://dcpd6wotaa0mb.cloudfront.net/mdms/dms/Residential%20Insulation/10024567/10024567-PINK-Next-Gen-Fiberglas-Insulation-Product-Data-Sheet.pdf?v=1620714258000

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