Rigid foam insulation against lathe / canvas

[willothenorth]

Hi y'all,

I'm located outside of Fairbanks, AK.

I inherited (bought) a 30' pacific yurt when the owner, who had set it up on our property, moved away. They had purchased it used. They tried to live in it the first winter they had it but it was not tenable, despite the "full insulation" package-- that business cannot stand up against -40 and -50. Didn't even really hold up against -15. There were other problems they dealt with-- their woodstove install had some tight bends in the stovepipe and it didn't draw well, the oil drip stove they set up had the same. Trying to heat whatever cubic footage a 30' yurt is was just not happening.

I bought the yurt from them last summer with the intention of revamping it and making it livable. Either by setting up a smaller interior space to heat, by adding

insulation

to the walls, or all of the above.

I'm at the point of adding

insulation

. I'm also framing the walls on the inside (adding support 2x4's to each rafter at the walls) out of necessity, to protect the structure against heavy snowfall. My insulation plan was to utilize a combo of rigid foam + fiberglass insulation between the support 2x4's, and then add vapor barrier + either drywall or plywood wall panels. I decided this after seeing a couple threads on here about insulation practices for various yurts.

I left a 1.5" gap behind each 2x4, which means I can run the rigid foam behind them continuously and hopefully avoid thermal whatsit, conduction? I had left the gap originally just to provide the same depth for insulation as you'd have with 2x6's, but having learned about thermal conduction after installing half the posts, seems I (maybe) lucked out to be able to run rigid foam continuously behind them!

Except, here's my query: since the way I am doing this has the rigid foam butting up against the lathe, that means there will be an air gap between the outer layers of canvas (and included "space" insulation) and the rigid foam. FWIW I am using R-Tech foam with R-9.6. It's doublesided with reflective... stuff. (Can you tell I'm on the learning curve here??)

I'm concerned that I'm going to create a

moisture

trap between the canvas and the rigid foam, particularly since it sounds like this style of rigid foam IS a vapor barrier. I just paid a lottttttt of $ for this foam so I'd really like to make it work. Will the canvas layers breathe enough to not make this a worry? Should I take out the lathe to reduce the gap? Should I use the fiberglass first and keep the rigid foam on the interior to act as my vapor barrier?

Any thoughts on this would be really appreciated! Fairbanks is pretty dry, so I'm hopeful that will work in my favor. Thanks in advance for any advice folks may have.

-Will