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Double-Stud Wall Simplified; Low Cost, High Performance thoughts?

| Posted in Green Building Techniques on

Greetings,

This is my first question while I’ll been a reading of this blog for some years now. I live in the Ottawa, Ontario region which is in zone 6 and I’m in the process of designing a house with the pretty good house approach in mind. I prefer simple construction methods and details that would allow me to take on as much as I can while what ends up being contracted out is something easily buildable that any contractor should be familiar with.

This brings me to the good ol double stud wall. We here to this day still have a passionate discourse about everything from dew point, permeance, OSB sheathing getting wet and the importance of attention to detail for the integrity and performance of your dense-pack cellulose wall system. There is builder in Quebec called Rocket Construction who uses no structural sheathing much like the guys at 475 High Performance have shown in this project: https://foursevenfive.ca/blog/project-spotlight-three-tree-builds-high-performance-house-without-sheathing/

And here are the details from Rocket Contruction:
https://a0101aa3-8c16-4faf-8079-2dc1531fecc4.filesusr.com/ugd/cf4fee_cfbfd446af554da1b72711c9d6673488.pdf

What do you guys think of such simplified systems?

William

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Replies

  1. Arnold K | | #1

    Hi William,

    I'm also from Ottawa, Canada and will be starting my house build this summer using a double stud wall with exterior rigid insulation. I have decided to use BP Excel Extreme Sheathing because it has been used by a local architect with success and it can also be a air barrier if tapes.

    In the above linked wall assembly, they use SONOclimat ECO4 (similar to BP Excel Extreme Sheathing) which is also a structural sheathing but also has insulating properties of R-4 per inch.
    As for 475 High Performance method, they forewent the sheathing and simply used diagonal bracing for the walls and roof.

    SONOclimat ECO4 specs:
    https://eco-building.ca/wp-content/uploads/2019/07/T12670-106_SONOclimat_ECO4_En_08-14636585404223102286.pdf

    BP Excel Extreme Sheathing specs:
    https://bpcan.com/wp-content/uploads/2018/04/tds-excel-18-04-2018.pdf

    Arnold

  2. Expert Member
    Malcolm Taylor | | #2

    William,

    I don't see much that is simple in those building assemblies.

    - The foundation appears to have top-bearing floor trusses resting on a knee wall supported by foam.
    - The wall system substitutes a layer of interior fibre-board (I'm assuming it's structural) for the sheathing, but also has two layers of strapping on both the interior and exterior. I see no advantage to the interior strapping (which isn't deep enough for services), and on the exterior sheathing would have been fine as long as a rain-screen gap was included.
    - The roof has a very difficult to build sandwich of membrane and strapping. Staging that roof without sheathing is something for adventurous builders.

    I'm pointing out these things because they represent large deviations from the standard construction in your area, and I don't think they add much. And because I agree with you that the simpler the assemblies, and the closer they are to what builders in your area are familiar with, the better your chances of success.

    My advice would be build the house much as all your neighbours did, and then add an additional interior 2" x4" walls that you can locate at whatever depth you want to get the double-wall R value you would like.

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