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The most value-engineered siding furring strips over thick rigid foam… but what width?

mackstann | Posted in Green Building Techniques on

Assuming labor is free, I’ve found that the cheapest furring strips would be 15/32″ plywood. It’s quite a bit cheaper than 1×4’s (less than half the price, close to a third, if ripped to 2.5″), and can be narrower than 3.5″ without worrying about splitting like 1×3’s or 1×2’s would. Also, it just barely meets the 7/16″ penetration requirement that James Hardie has.

But how wide should they be? 2.5″ seems like a reasonably safe width, but I’m curious if anyone has real-world experience with smaller furring strips, and can comment on how small is too small.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Nick,
    2 1/2 inches sounds OK to me. But I must say that I am surprised that James Hardie is happy with only 7/16" inch penetration of fasteners. If ring-shank nails are an option, I would select them over smooth-shank nails.

  2. PAUL KUENN | | #2

    I also use 19/32" for less nail "bounce" and at $17.5 for a 4x8 sheet ripped at 2.5", I get 19 furring strips @ $0.92. That's half the price of locally sourced 1x4" strips at $1.98 per. I do use "used" ring shanks from Habitat's ReStore for next to nothing (sometimes they clear the shelves for 25 cents a pound.
    Cheers,
    PK

  3. mackstann | | #3

    Thanks for the real world experience, Paul.

    Martin, the 7/16" number was surprising to me too, but it is your article and you even followed up about it in the comments. :-) In their documentation, the 7/16" number is given for OSB sheathing -- it doesn't say anything about furring strips. The nail is also required to be quite a bit longer and penetrate well past the inside face of the OSB. But you said the rep was confident that that requirement also applied to furring strips, so I am taking that at face value.

    I don't live in a very windy place, and I'm surrounded by trees and houses in an urban area, so I feel fine going with the bare minimum requirements for wind resistance.

    But I would definitely be using ring shank nails.

  4. Expert Member
    MALCOLM TAYLOR | | #4

    Nick, With Hardiplank it isn't the wind that will cause the problems, it is applying enough pressure at the fasteners to hold the board tight to the one below. I think you risk having gaps with what you propose.

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