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Furring strip size

Slivy | Posted in General Questions on

Hey everyone. I’m helping a friend rebuild the exterior wall of his bathroom (a 1930sish addition to a 1890s house in north Georgia). I’m using the method laid out in Martin Holloday’s article “5 Rules for Wall Design.” I’ll post the link here:

Five Rules for Wall Design

I’m installing hardiboard lap siding. My question is this: What size furring strip should I use? Also, I know i need to connect the 2″ foam to the wall studs (through a zip wall panel)–would 3.5″ screws suffice or should i use 4″?
And for the siding (which is about 1/2″ thick) should i use siding nails that pass through the furring strips or just go halfway? I’m assuming the furring strips will be only about 1/2″ thick themselves…but I wanted to check with y’all first.
Thanks so much.

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  1. Expert Member
    1. Slivy | | #3

      you can ignore my second question. Found it on page 16 of the document you sent.
      looks like my hardieboard siding is classified as "light weight." So, from my reading of the tables, a treated 1x2 would be sufficient?
      Thanks again. Really great resource.

      1. Expert Member
        MALCOLM TAYLOR | | #4


        You bump into a bit of a quandary. The guide I linked to is dealing with the structural implications of hanging the siding, but the manufacturer of the siding may have additional requirements. While those may not be practically important, not meeting them might have warranty implications.

      2. Expert Member
        Akos | | #6

        I would not use anything less than a 1x4. The thinner wood tends to split. You also don't need treated wood behind siding, standard SPF or plywood works just fine.

        For your corners, best is to rip wider strips of plywood so they can reach back to the corner stud behind the foam. So with 2" foam, you want 4" wide strips.

  2. Slivy | | #2

    Hey thanks so much. These give a lot of great detail. And got no idea how you found that so fast.
    So, it's probably buried somewhere in the text, but I've one more question now--how to classify the weight of my hardiboard siding. I'll attach the the diagrams from the article i'm referring to. (pages 20 & 21).

  3. Expert Member
    BILL WICHERS | | #5

    The usual rule is the screw needs to be embedded at least four times its diameter in the wood, and that’s for the main body of the threaded portion of the fastener not including the tapered point portion. In practice you generally want at least 1” of fastener embedded in the wood, 1.5” is better for a bit of safety margin.

    Work out how thick the entire assembly toured hanging off the wall will be, then use a screw long enough to penetrate all of that assembly and still to 1.5 inches into the stud.


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