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Attaching 1″ Rigid Foam Under Hardie Plank Lap Siding

brandon! | Posted in General Questions on

Apologies if this has already been asked and answered. Searched the forum but without more detailed filtering, there’s simply too many results to read through (10,000+).

We’re currently building a new detached garage and planning on installing 1″ continuous rigid foam on the exterior. Per Hardie’s guidelines, up to 1″ is approved with or without firring strips. We are not using firring strips (not an option at this time).

My question is, what is the recommended fastener, screw*, nail*, adhesive or adhesive and one of the former?

*Assumes foam washers; e.g., SPAX1.75 in. x Plasti-Grip Ci Prong Rigid Insulation Washer

For reference, our wall breakdown is:

  1. 1/2″ fire rated drywall and/or plywood (French cleat system)
  2. 2×4 studs w/ 3.5″ rockwool
  3. 1/2″ OSB
  4. WRB
  5. 1″ rigid foam board
  6. siding

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    I use whatever cap nails the lumberyard stocks.

  2. Chris_in_NC | | #2

    The siding is going to do a great job of attaching the foam to the sheathing/studs. You just need a temporary attachment method for the foam until the siding goes on.

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