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Foam strips as furring for rain screen.

blamus20 | Posted in Green Building Techniques on

I’m looking at the different solutions to fasten 2″ foam to zip sheathing and studs, followed by a rain screen and corrugated metal siding. 

I see that the most common practice is to use 1×3(or 4) wooden furring strips to secure the foam to the studs, and then the siding screwed to the furring strips. fastener type and length can be determined by one of these tables:

What I’m wondering is the possibility of replacing the wooden furring strips with strips of 1/2″ foam. In effect, that would be fastening the siding directly through 2.5″ of foam into the studs. One would need a 4″ screw to achieve 1.5″ of penetration into the studs, likely a #10 x4″. Securing siding directly through foam of varying thicknesses into studs (without wooden furring) is documented in the above article. So has anyone done this and is this a bad idea?

I’ll be running corrugated metal siding horizontally, so I’ll need vertical furring. The fact is that the quality and cost of lumber is going through the roof and a piece of 1×4 at for example home depot is $5 a piece! If strips of polysio or XPS can be used to create this rainscreen gap, it’d be a fraction of the cost (4×8 1/2″ is $13, which can make 16 strips of 3″ wide foam furring). Cutting it will be a pain, and holding the foam/foam strips up before the siding gets screwed through will be a bit fiddly and probably need some capped screws. 

Benefits other than material cost include actually more overall insulation, and not having to worry about the wood strips splitting during installation (likely) and deteriorating over time because its thin and not treated.   


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  1. charlie_sullivan | | #1

    That sounds like a pain. It could break or squish when nailed as well as being hard to cut. And it would be utterly irresponsible to use XPS for that given the climate impact.

    I've seen coroplast used (example That's a little more expensive than foam (at home depot prices) but I'd have more confidence in it and I think it would be easier to work with.

  2. andy_ | | #2

    Compression is the issue that comes to mind. The foam would have to be really dense to achieve enough rigidity for the siding. The wood strips spread the load over the foam so it's not a problem there.
    Wood strapping might split if you nail with framing nails vs siding nails, but you can blunt the tips of the nails with an angle grinder. ...not ideal, but it works. Plywood strips are not prone to splitting.

    1. blamus20 | | #5

      You must not have been following the prices of plywood lately :P

      Almost $50 for CDX and a lot more for advantech. 7/16 zip is now $45....... I'd have poured the entire house out of concrete if I knew how lumber would double in cost like this! (or bought a lot of stocks for that matter)

      1. Expert Member
        MALCOLM TAYLOR | | #7

        Crazy isn't it. OSB hit $50 CDN last week. If you had a muddy site you used to throw down a sheet to walk on. I bet no one is doing that anymore.

  3. Expert Member


    - Remember that you are using gasketted fasteners to secure the corrupted metal siding - which rely on compression to maintain their seal. That means the consequences of the foam substrate squishing are much larger than if you were just nailing on some other material.
    - I agree with Andy. You can get 24 pieces of strapping from a sheet of plywood.
    - Installing corrugated metal siding is a lot harder horizontally than vertically. Think through what trim you are going to use and the sequence carefully before starting.

  4. blamus20 | | #4

    Thank you for the heads up. If compression is a problem then the siding will have to be fastened to furring instead of all the way through to the studs. I imagine the coroplast is even more squishy than the polysio I'm using, even though the cost is STILL cheaper than untreated 1x4's......

    1. charlie_sullivan | | #6

      I didn't notice the metal siding note, or didn't pay attention. Given that, forget my coroplast suggestion, unless you want to go shopping for heavy duty coroplast. I'm sure that exists but I doubt you'll be saving money at that point.

      One other thought is that if you can find the right person's plywood scrap or other scrap wood it might be in a form you can use.

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