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Small Cabin Forum / Cabin Construction / Critique my wall/roof assemblies
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Nate R
# Posted: 3 Dec 2018 10:18

Critique my assemblies!
Narrowing down my materials list for a build, putting everything through ResCheck again, etc. Before I get a permit next spring, just trying to hammer out more details.

PART TIME recreational cabin. Single story, no loft. Trying to find a balance between a functional wall, relatively energy efficient but not TOO much where the stove cooks us out of a small cabin, and not TOO expensive, but aesthetically tolerable to us. Northern WI climate. All 4 seasons, snow, but not TOO hot in the summer.

Concerns: A lot of the stuff about air barriers, vapor drive, etc seems to be a bit different when you're not running air conditioning in summer, or only adding moisture inside in winter occasionally. This is an off grid place, no interior bathroom. Will be built on an insulated slab w/ vapor barrier underneath, so from what I've seen in another cabin in the area on an UNinsulated slab, it WILL stay higher than outside ambient in winter, maybe hovering around 30 degrees inside.
I plan to heat with wood primarily. No A/C. Only used a few times a winter (maybe a few weekends, or a week and a couple weekends), and then weeekends, etc throughout the rest of the year. Thus, it won't be heated full time or see full time moisture loading from interior occupants.

Walls, outside to inside:
Cement Fiber Panel Siding
WRB taped as air barrier (Benjamin Obdyke Hydrogap)
7/16 OSB
2x6 studs, 24 OC. Advanced framing headers (insulated.). 8 foot walls with double bottom plate (state code to overhang foundation insulation)
R23 Mineral Wool Batts
#15 Tarpaper, large laps. POSSIBLY taped? (moisture reservoir, and some areas may use barn boards or boards with gaps as interior finish, so this is also to keep the gaps from being too eye-catching.)
Wood interior, much of it T&G.

6/12 Asphalt shingle roof, 5/8 OSB Sheathing.
Scissors trusses, with slightly raised heels. (~8" heels.) Ventilation channels over plates, possibly made from XPS. Soffit vents (continous) and a ridge vent.
R30 Mineral wool batts between the bottom chords. I'd go thicker, but can't find mineral wool batts with higher R Value. And I'm not a fan of FG. And, off grid, rural..blown in insulation would be a real hassle to get in there, power for the blower, etc)
R3 XPS sheets on the INTERIOR of the bottom chords. (Thermal break. Some of these trusses will be over a porch as well, so trying to keep them from bringing that cold right to the interior)
Thinking T&G right over the XPS on teh ceiling? Maybe a layer of #15 felt in between again for visual purposes. (XPS SHOULD keep vapor flow to a minimum. COULD tape seams on XPS.

Curious on thoughts with this. Suggestions on why certain things might not be a good idea, etc. Easier to debate now than when I have materials in hand waiting to be built!
Thanks for any input!

# Posted: 3 Dec 2018 10:49

Sounds good to me...although I build in the dry warm southwest.......Seems like you've got the knowledge to get going. With my remote cabin, I did it in stages (due to my time constraints and budget) that gives ya some time in between to think about the next step, or modify the last step. Take it slow, do it right, you only get one chance! And enjoy. And take a lot of pics for us, even chronicle your build here on this forum for posterity....? I did and it's nice to be able to send friends here to look at what we built...

# Posted: 3 Dec 2018 19:15

I would go over to the Green Building Advisor forum, join for free and post this exact question. Just click on the "Ask a Question" button in their community forum.

You can also look up articles on "how to insulate under a slab", how to insulate an attic" etc (or any other topic).

Nate R
# Posted: 4 Dec 2018 10:52

Good point, Rockies! I've been there enough to check out other stuff on that site, might as well get feedback there. And haven't seen their stuff on slab insulation, should probably look that up.

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