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Bonfig Wall Assembly

Tony Rigdon | Posted in Green Building Techniques on

I have a 1920’s two story house, all the walls are metal lathe and plaster. I’ve left the first floor as is for now and have it rented out. On the upstairs, I’m currently removing all the lathe and plaster with the plan of installing R19 fiberglass batt insulation after building out the 2×4 studs using the “Bonfig” approach to break the thermal bridging of the studs. My original plan was to use 1″ foam board insulation and either 1×2 furring strips, or 3/4″ plywood strips. But then I started thinking maybe Zip R sheathing would be a great option, ripping 1.5″ strips of that instead, anyone have strong opinions on these options? The utilities on the first floor are all in my name still, set price on the rent, so I have a strong financial incentive to make the second floor a well insulated “hat” on the house!

PS – I’m in Climate zone 4 (Columbia, Missouri)

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Replies

  1. Expert Member
    DCContrarian | | #1

    Zip-R is very expensive and the foam is not glued that well to the board. In narrow rips like that I think it would fall off a lot of the time, which doesn't really save you any effort.

    1. Tony Rigdon | | #2

      Thanks for the reply! I hadn't considered that the foam isn't glued well and that does make sense with the thinner strips it would likely come off. I'm looking at $56 for the 3/4 plywood and $25 for the 1" extruded polystyrene, so I was figuring it would probably be similar to the cost of Zip-R, but haven't checked the exact price yet. Pretty sure I won't do the furring strips, seems more likely to split once I start driving the drywall screws into it!

      1. Expert Member
        Malcolm Taylor | | #3

        Tony,

        I think the OSB on Zip-R is just 7/16", so an apples to apples comparison would use that as your furring, not 3/4" plywood.

      2. Expert Member
        DCContrarian | | #4

        The Zip-R comes wrapped in plastic and in the instructions it says to use promptly after opening or the foam will fall off. The glue is really just to keep the foam attached long enough to get it nailed to something.

  2. Andy S | | #5

    Having done a Bonfig wall I learned a few things...
    1x3 strapping will split when nailed way more than 3/4 plywood. The 1x3 will also get in the way of batt insulation.
    Get a very high density foam, anything the box store carries will deflect at the ends when nailed creating an uneven wall that will need shimming before drywall.
    It's labor intensive, but you're DIY so less of an impact on the budget.

    If you're really looking to save the money on heating, I'd look at air sealing first (especially ceiling to attic and basement to first floor) and then at insulating up in the attic. You'll get a lot more bang for your buck there.

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