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DannyDan
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# Posted: 21 Jun 2017 01:34pm
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Hi this is my first post, I'm hoping I could get some knowledge from others as I can't find recommendations specific to my situation. I'm trying to determine if I will have any problems using drywall in a Derksen portable cabin I plan to put by the lake and use seasonally in the summer time. It seems many recommend against drywall in seasonal cabins, but the issues seem to be related to heating seasonal cabins in cold climates.
What are the cons of using drywall in a seasonal lake cabin in Oklahoma that will not be heated but will be air conditioned?
Is a vapor barrier something I need to worry about? The building won't come with one already installed and I believe the "warm side" is the outside in Oklahoma, especially in my seasonal use case. Is this something to worry about?
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Absolutely
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# Posted: 21 Jun 2017 08:58pm - Edited by: Absolutely
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I've had drywall in an unheated / unaircondtioned seasonal use cabin for more than 15 years. Other than some cracking at some joints when the cabin was re-set on its foundation, it's been fine. I used a 6 mil vapour barrier behind the drywall to control insects.
I can't see there being any issues with a normal stud wall with insulation and vapour barrier behind drywall surviving unheated over winter. Just my $0.02.
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rockies
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# Posted: 21 Jun 2017 09:39pm
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I would read some of the articles on the Green Building Adviser website about vapor barriers and retarders. Most of them recommend not using 6 ml poly on the inside since it can trap moisture in the wall cavities.
There is also the issue of "in which direction the warm moisture is moving through the wall"? Most people deal with warm, moist interior air escaping through the wall to the cold dry exterior in winter. You're concerned about warm moist exterior air being driven through towards the cooler drier interior. That creates a different design situation for the wall.
Hopefully these articles will help.
http://www.greenbuildingadvisor.com/blogs/dept/musings/vapor-retarders-and-vapor-barr iers
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/smart-vapor-retarders
http://www.greenbuildingadvisor.com/blogs/dept/musings/do-i-need-vapor-retarder
http://www.greenbuildingadvisor.com/blogs/dept/musings/when-sunshine-drives-moisture- walls
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Jabberwocky
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# Posted: 22 Jun 2017 09:18am
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I second Rockies' suggestion. Green Building Advisor has been an invaluable help to me.
As I understand it, installing poly on the inside of the wall assembly is basically a no-no, especially for our climate.
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DannyDan
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# Posted: 22 Jun 2017 01:14pm
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Thank you all for your help and comments. I'm confident that no vapor barrier should be installed on the inside and also that it's not super necessary to install on the outside to the point that warrants taking off the exterior paneling to install a VB. The building will have a lot of trees around it and will be a light color, so solar driven moisture should be low.
I would have liked to use Rmax R-Matte Plus-3 3/4 in. Polyisocyanurate Rigid Foam Insulation applied on the interior side of the studs with the reflective side facing the outside wall, and putting 1/2" drywall over it. However, the datasheet for the product shows it has <0.3 "Water Vapor Transmission". Does this make it a vapor barrier and thus a poor choice?
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DannyDan
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# Posted: 22 Jun 2017 02:30pm
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Nevermind, it looks like it does act as a vapor barrier: http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/can-exterior-foam-insulat ion-cause-mold-and-moisture-problems
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rockies
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# Posted: 22 Jun 2017 07:33pm - Edited by: rockies
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For insulation you should use Roxul Comfortbatt, which is a mineral wool insulation that doesn't hold water and is also fireproof.
Rigid insulation in the wall cavity (or attached to the interior surface of the studs) could also trap moisture between the insulation board and the sheathing.
If you want to add an air barrier to the inside (which would also help prevent interior vapor from migrating through the wall) I would use a semi-permeable barrier like CertainTeed Membrain.
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DannyDan
Member
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# Posted: 22 Jun 2017 08:19pm
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Is there a downside (other than efficiency) to just adding drywall and painting it and not using any insulation at all?
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rockies
Member
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# Posted: 23 Jun 2017 07:28pm
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Well.......if you ever sell it the new owners would probably be grateful that it was at least a three season cabin. Plus the insulation does help prevent the heat from baking through the walls and roasting you out.
Of course, this all depends on if you put any effort into making the structure sound. Too many people head down to Home depot, grab a bunch of 2x4's and then go out into the woods to slap something together without bothering to find out about proper structural support.
Either that or they start hacking apart a cabin that's been around for 30 years in order to "improve it" and they remove a load bearing wall or beam.
Build the best cabin you can afford and always try to go better than code. Someone someday will thank you.
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