Walls and Insulation

The walls of the house are going to be 2x6 construction with Roxul ComfortBatts in the cavities. The differences with this wall system begin with the vapour barrier. There isn’t one. We are not putting polyethylene on the warm side of the walls. The reason is that we are putting significant amount of outsulation (Yes it’s a word despite what autocorrect feels.) outboard of the exterior sheathing. Like, 6 inches of Roxul ComfortBoard. This keeps the whole wall system warm, and the condensation point within the wall will happen outboard of the exterior sheathing, which means, no water in the wall cavity itself. 1/2” plywood is the sheathing of choice for me, as the more wood like it is, the less it can fail when and if it ever gets wet. On the sheathing we are using a peel and stick membrane from Cosella-Dorken, Delta Vent SA. It is a weather barrier and air barrier all rolled into one membrane. It’s vapour permeable though, so if water did get into the walls, it can actually get out. That’s important. After the ComfortBoard, then 2x4 strapping and Fraser Wood Siding’s Evolution Series product. 

This wall system will stay warm, really warm, like R-36 kind of warm, which is awesome. If moisture was to condense from either direction, it should happen outboard of the Delta Vent SA, which will allow it to drain away. If for some reason water vapour did get into the stud cavity, it’s not trapped, it can migrate to either side of the wall system to escape. From Building Science Consulting, this is called The Perfect Wall. A vapour permeable or flow through wall system is how it can be referred to in natural building. Air seal it to an inch of it’s life, and allow the vapour to flow, keeping it outboard of your important stuff. That’s how it works. 

I want to make it clear, that the companies mentioned above did not pay me or give me any of their product at a discount or free or such. This is all above board because these products perform really well under the difficult conditions of being in a wall system. 

How difficult? Consider the walls are the same as a trip from Canada to Florida in winter. On one side it is 20C and on the other side it is -20C. Inside that wall it gets cold, wet, warm, dry, etc. And this all changes the forces (pressures, temperatures, etc) on the walls minute by minute, with sun, rain, snow, wind, etc. It’s really complicated, and if it’s not done right things fail. I know, I see them all the time. That is why I chose these materials, in this configuration, because they will perform better than others. Are there other solutions? Yes there are other solutions. I like these, so that’s what I’m using. 

So how do you install 6” of a rigid stone wool to a wall? Good question. Like this:

IMG 1841

Staggered joints on each of the 3” batts (3” is as thick as they come.) and secured with really long screws using the Delta dimpleboard washers. Now this is the basement detail, but the walls are the same. I’ll talk about the basement in another post. 

© Stephen Collette 2016