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Small Cabin Forum / Member's Projects and Photos / Mini Aframe - moisture barrier questions
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willywilly2020
Member
# Posted: 1 May 2024 13:35
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Hi! I'm planning a build with a friend. They want to whip up this mini-A-frame: https://drive.google.com/file/d/1N8UB2hlQet3FgP_o9OaSJs8-5xSSqo8B/view

My question: I'm worried about moisture in it. I was planning to tar-paper under the roofing, but not sure, given limited time for the project if we should do anything more. Long term they might want to insulate it, which would mean we want a good moisture barrier.

Any suggestions for how to relatively keep these plans but avoid mold / moisture issues?

ICC
Member
# Posted: 1 May 2024 18:25 - Edited by: ICC
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Quoting: willywilly2020
I'm worried about moisture in it.


Moisture from where?
From the exterior, such as rain?
From the interior, such as from breathing, cooking, using unvented propane space heaters?

Tar paper or house wrap under roofing material protects against rainwater infiltrating the interior from the exterior side, when installed correctly. Both of those are designed to allow water vapor to move through the membrane from the interior to the exterior. Properly installed either of those can also act as an air barrier.

Depending on the climate zone, if batt insulation of some kind is installed later, a vapor barrier inside the insulation may be recommended.

I did not peruse the plan document at all as I have trouble reading PDF files on the relatively small screen of my phone (compared to a computer monitor).

travellerw
Member
# Posted: 2 May 2024 01:56
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Our cabin is built with a fully sealed interior envelope. We even taped the staples. Accoustical sealant and tape where the plastic attaches to wood.

We have had no moisture issues at all. We do run the fire in winter (which really helps). We also keep a window cracked (or the fire will back draft badly due to how sealed the cabin is).

Brettny
Member
# Posted: 2 May 2024 07:04
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The link dosnt work.

I would avoid tar paper as it's really a crappy product vs a synthetic underlayment. I assume with an A frame there going to insulate in between the bays. To really get a good air seal (and you need one) your only good option is foam. If you can do even 1in of foam between the roof and rafters it's going to help a ton.

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