if you strip exterior walls, how do you do a vapor barrier and insulation properly?
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How do you re-do the insulation on a old cabin from the outside?
Raphael Couture
Sept. 14, 2020Last updated: Sept. 17, 2020
I'm planning on stripping the outside walls right to the studs in an old cabin in cold/very cold climate. It will be heated once a week in winter. There is no vapor barrier right now in the walls. Is it OK to install polyethylene on the backside of the studs, then adding fiberglass mats, finishing with Tyvek, furring and wooden exterior. Usually the vapor barrier is installed on the INSIDE of the studs, not on the outside. Any molding risks ?
Thanks !
Yeah, There is abig risk of mold the way you describe it.A vapor barrier needs to be installed on the warm side of the insulation. Putting a vapor barrier on the cold side of insulation means that warm humid air migrating through the wall will be stopped, it will then freeze, so in the spring you will have a ton of water in there. First have a look at this page here about how the control layers (thermal barrier, vapor barrier and air barriers) work in a wall -
Building science made easy video– How to design walls that work properly
既然你是逆向设计，也就是从外部建筑，我假设你已经完成了内墙，你不想弄乱，这是一个正确的假设吗?这当然更棘手，但要正确地做到这一点并非不可能。我建议有几个选择，第一个也是最简单的——你可以从外面喷泡沫，然后重新涂上护套，一个天气屏障(WRB)，然后外墙。我们通常不推荐喷射泡沫，但对于一个小舱室来说，从外面喷洒泡沫可能是最好的解决方案。如果这不是一个选择(意思是——如果你的客舱太偏远了，你无法安装喷雾泡沫安装器)，那么我会做你必须做的，在那里安装一个蒸汽屏障。This is less than less than ideal, but you could apply the vapor barrier first (going in and out over the studs) then install the insulation afterwards followed by sheathing , WRB and siding.
Here are a few pages I think may be of value to you, check them out and then let us know if you have more questions –
Choosing the right weather barrier WRB
Spray foam insulation with eco-friendly safer blowing agents with low greenhouse gas emissions
How to install siding so walls can dry
The way you describe the vapor barrier is what I had in mind. It would still be on the warm side of the insulation, but on the outside of the studs instead of inside like usual. That was the area of concern (the studs).
Ok, Great to hear. with a re-read it makes more sense, glad we're in agreement! Best of luck with it Raphael.