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Build my own SIPs, or just frame it?

Mathew BEAN | Posted in Green Building Techniques on

I am in the planning phase of building a second home and a shop on my property. I have access to as much insulation material as I need in 22″ wide and various length (from 36″ to 64″) rigid foam insulation (door cut outs with the skins still on r 6.25 and 1 3/4″ thick) for free!

Thinking of either constructing sips panels by using construction adhesive to glue the pieces together inside of a plywood and dimensional lumber frame or just framing a double stud wall and filling in the void with the insulation. I am planning on R30 or better exterior walls. Property is located in climate zone 4c.

Building will have to be engineered anyway because of other issues so I would not anticipate a significant change in cost based on which method I use to construct the walls. I also don’t anticipate a large materials cost difference between the two methods (but some careful math is in order).

Finally, if I decide to go with 2×4 framing, I plan to install 2 layers of the insulation on the exterior of the home prior to installing building wrap, rain screen and siding. Other than added labor and trim/ flashing issues is there any compelling reason not to consider this method as a way to prevent thermal bridging etc.?

For a novice builder which method would you recommend as more feasible for construction, permitting and long term durability?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Mathew,
    I think that the hassles associated with building with these scraps outweigh the advantages. You will end up with a much better project, with far less labor, if you purchase used (reclaimed) rigid foam in larger sizes from a foam recycler.

    With these small pieces of foam, you'll need lots of expensive canned spray foam or European tape for air sealing.

    You certainly won't be "building your own SIPs," since SIPs are structural (in a way that your cobbled-together panels will never be).

    If you go forward in spite of my warning, I advise you to build a house with conventional 2x4 or 2x6 walls, and then to install the foam scraps on the exterior side of the wall sheathing, in as many layers as your patience permits. Don't try to insert these scraps between studs.

    For more information, see How to Design a Wall.

  2. Jim Tyler | | #2

    I agree with Martin that you should consider a standard wall with exterior foam sheathing. With such short pieces, maybe consider framing on 16" centers so that each piece of foam gets at least a couple pieces of strapping across it. I built my house with two layers of ~20" x 8' x 3" foam, and for sure it cost time vs 4'x8' sheets, but it was a pretty smooth process. I focused on air sealing at the plywood sheathing layer with gaskets and tape, and used spray foam between foam boards. You will for sure run into some time consuming problems to solve, and recycled foam is relatively inexpensive. Always satisfying to use something you got for free though. Good luck with your project!

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