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New Wall Assembly

Posted by Jodi on August 22, 2016

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Here's our current diagram to show our proposed wall assemblies:

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R35 Wall Assembly

The problem with the R25 (R15 plus 10 code wall) is that the exterior insulation is expensive, complicated to install, requires specialty fasteners, and the builder needs to do some tricky things with the air sealing and the window installation. It's a pretty labor-intensive and expensive way to get R25. So, we are thinking about an easier way to assemble the structure - using a builder to put up the house quickly and then work on all the interior layers ourselves -- indoors and out of the elements and bugs. Rachel Wagner (Wagner Zaun Architects) presented this alternative at the 2016 Duluth Energy conference and we are thinking about a variation on this approach. It seems like a pretty simple way to get to ~R40. Here's the layers we would use: BUILDER TO INSTALL: 1. Vertical Siding with more that 3/8 in air gap. Eliminates rain screen complexity 2. WRB - Tar paper 3. External Plywood Sheathing - windows and deck attach to this lay...

R25 Wall Assembly and Vapor Retarders

One wall option is to scale back the double stud wall to a single stud with a layer of exterior insulation. This approach should end up at an R25 wall and still allow it to dry to both sides. The diagram below from Building Science Corporation shows where we are going -- except replacing the 2x6 wall with a 2x4 wall so we can use a class III vapor retarder (latex paint) The table below outlines the required exterior insulation thickness to eliminate the layer of poly -- and just use latex paint as a vapor retarder. Mineral wool board has an R value of about 4. So, we will need about 3 inches on a 2x4 wall. Some other good reading on Vapor Retarders and what is required: http://www.greenbuildingadvisor.com/blogs/dept/musings/vapor-retarders-and-vapor-barriers http://www.greenbuildingadvisor.com/blogs/dept/musings/do-i-need-vapor-retarder

Minimalist Trim and Drywall Edges

We are not planning to have a lot of trim around windows and doors - it's just more to dust and more expense to build. One of the Wagner Zaun homes just used the door jams - we thought that was interesting.... A number of homes with thick walls just run the sheetrock up to the windows. This seems simple, but there's details to think about in how the windows are constructed and how the rock/mud will meet up with the windows. There's a special type of "hot" mud - 90 minute mud that may not crack as much as traditional drywall mud - because it cures with a chemical reaction. We also like the look of rounded drywall corners on the windows - to reduce the sharp edges.

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