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CentralWiCabin
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# Posted: 7 Jun 2015 02:29pm
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Hello everyone. Been following this site for ideas and dreams. I am currently building a cabin that will have spray foam in the floor, walls and roof. The footprint is 15' x 38' with 2 x 6 walls and energy trusses for the roofing support. The current plan is to frame the trusses like a pole barn. 2 x 4's across trusses and metal roofing screwed to those - no plywood sheathing. What I am unsure of is how to insulate this configuration so we don't have issues with moisture. Any suggestions? Thanks.
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Salty Craig
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# Posted: 7 Jun 2015 04:07pm
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I would advise to leave an airspace under metal for airflow. That will allow quicker drying of condensation in the morning. As the morning sun hits your metal, it will condensate a little on under side. Make sure you use vented sealer strips under the ridge cap.
As for insulation, that's up to you. The more the merrier. Would be a good idea to use 8" rafters so you can install R21 insulation bats with room to spare. I'm not fond of spraying under roof metal. That stuff will rust in short order.
You can fill the void full if you first install the styrofoam air channels. Not sure what there called. Just don't block airflow.
My 2 cents worth. Have fun.
Salty Craig
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CentralWiCabin
Member
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# Posted: 7 Jun 2015 04:40pm
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I've been thinking about it some more. Maybe it would be better to leave the attic space unconditioned. Install ridge vents and soffit vents and insulate the ceiling instead - using the air "chutes" to keep the insulation from blocking the upward movement of air.
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Nirky
Member
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# Posted: 7 Jun 2015 09:20pm
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If you opted for spraying closed-cell foam, it's R-5.5 per inch thickness. 2x6 wall would be R-30, all the temperature resistance you need. Plus it's its own vapor barrier, do not need to worry about airflow for any sealed areas. Downside is it's a bit expensive.
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Trouthog
Member
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# Posted: 9 Jun 2015 12:23pm
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When considering cost is the spray 2xs???
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