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Attaching exterior insulation

canadianexpy | Posted in Green Building Techniques on


I am looking for the best way to temporarily attach my exterior insulation to the sheathing. I am installing 2 layers of 3″ polyiso staggered, with Tyvek (WRB) on top of the foam and then 3/4″ furring to hold it all in place permanently. My furring is being installed horizontal as I am installing vinyl board and batten siding.  
I was planning on using a couple 3.5″ cap nails to hold the first layer, my concern is how to keep the second layer in place, while I install the Tyvek and furring strips.? 
I have not been able to find 6.5″ cap nails and I don’t think ” nailing” into the first layer would hold it. 
Any ideas or advise is appreciated,
Thanks Dave

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  1. GBA Editor
    Martin Holladay | | #1

    Cap nails are sold in a variety of lengths up to 8 inches long. Here is a source:
    Simplex cap nails

  2. canadianexpy | | #2

    Thanks, although that site is not working for me.

    Not sure I can get them up here in Ontario.

    Is the capnail the normal way to attach the second layer of insulation.

    1. GBA Editor
      Martin Holladay | | #3

      I'm not sure why that link doesn't work for you -- it works for me.

      Yes, cap nails are the usual method used. If for some reason you're having trouble finding long cap nails, try visiting a roofing supply house. In a pinch, you can just buy plastic insulation washers, and use any old long nail with the washers.

      1. canadianexpy | | #4

        Thanks Martin
        I will look into that option

  3. canadianexpy | | #5

    So has anyone used an adhesive to attach exterior rigid foam insulation to sheathing and to other foam. Mine is a 3" papers/fibreglass face polyiso.
    I have tried finding 3 1/2 cap nails and larger 6 1/2 but have had no luck here in Ontario.
    The link Martin posted, doesn't work for me, I have tried different ways but maybe being in Canada it won't work??? ( They might not deal with Ontario anyway)
    I will be attaching furring strips for final attachment of foam

    1. GBA Editor
      Martin Holladay | | #6

      Here's a source of cap nails in Ontario:

      I don't know which lengths they stock.

      Undoubtedly, roofers in Ontario buy cap nails. You need to find out where the roofers get their supplies.

  4. GBA Editor
    Martin Holladay | | #7

    Here are the Ontario locations of Beacon Roofing Supply. I don't know if they sell cap nails, but they should.

    Cambridge, ON
    42 Raglin Place
    Cambridge, ON N1R 7J2
    PH: (519) 624-8703
    Watt: (877) 750-1750
    Fax: (519) 624-1300

    Concord, ON
    8400 Keele St #1
    Concord, ON L4K 2A6
    PH: (905) 761-1762
    Watt: (800) 387-3195
    FX: (905) 761-0834

    London, ON
    1285 Hubrey Rd,
    London, ON N6N 1E2
    PH: (519) 685-0666
    Watt: (866) 710-5008
    FX: (519) 685-1355

    Ottawa, ON
    2801 Sheffield Rd
    Ottawa, ON K1B 3V8
    PH: (613) 744-5119
    Watt: (866) 268-1003
    FX: (613) 746-0839

    Whitby, ON
    202 South Blair Street #36
    Whitby, ON L1N 1A7
    PH: (905) 666-5648
    Watt: (844) 237-6150
    FX: (905) 666-0795

    1. canadianexpy | | #8

      Thanks Martin

      I will try some of local ones on Monday, it seems 3" is the longest most have.
      The first link was Ontario California, which I am sure you caught after posting, but I am sure they would have had what I needed.
      As I said 3" seems to be the longest of any cap nails available around me, what would a roofer use long cap nails for?

      1. Expert Member
        MALCOLM TAYLOR | | #9
        1. canadianexpy | | #10

          Thanks Malcolm,
          I will look into this, hopefully I can find small 6 1/2" nails, I don't want spikes. :)

          1. Expert Member
            MALCOLM TAYLOR | | #11

            Might be worth using something like GRK R4 screws. I think they stock them at most Lowes.

  5. seabornman | | #12

    I bought a box of 500 plastic caps from Amazon. I used them and a variety of lengths of deck screws for securing foam layers as I went. The caps have a fairly small diameter, but 2 or 3 in a sheet of insulation held even when it got windy. A lot easier to hold a sheet and operate a screw gun rather than a hammer when you're working by yourself!

  6. canadianexpy | | #13

    Thanks Joel, I thought about doing it that way, since I am doing it myself. Not sure if they make small 6 1/2" screws.

    Malcolm, I am using GRK screws for attaching the furring strips, there a little pricey for temporary fasteners. Thanks

  7. canadianexpy | | #14

    So strike out so far for getting a cap nail larger than 3" at least here in Ontario, Canada. ( Tried 6 different roofing supply companies in my area) I
    Any Canadians ever buy long cap nails???
    I going to try Simplex, but I have to change my IP address just to get on there site, not sure what that's about?
    Anyone else has any ideas to temporarily attach 2 layers of 3" paper face polyiso to my sheathing, I am all ears, I didn't think this would be the problem in building a energy efficient house!

    Thanks for any ideas or suggestions.....

    1. Expert Member
      Akos | | #15


      Call Spar Marathon and ask for deck screws. They come in either 6" or 7" no 6 1/2.

      1. canadianexpy | | #18

        Thanks, they didn't come up in my Google search.
        But they have 7" screws! $150 per 500
        Thanks again saved me!

    2. GBA Editor
      Martin Holladay | | #16

      Q. "Anyone else has any ideas to temporarily attach 2 layers of 3 inch paper-faced polyiso to my sheathing? I am all ears."

      A. Unclog those ears! Two and a half weeks ago, on March 22 (in Comment #3), I wrote, "You can just buy plastic insulation washers, and use any old long nail [or screw] with the washers."

      1. canadianexpy | | #19

        Martin I was told you're not supposed to use Q-tips in your ears!!!

        Unfortunately in a small town you ask local lumber yard for a 6/7" screws or nails, they hand you a spike or a timber screw. And when I tell them it's needs to be smaller and for exterior insulation, they look at me like I have two heads and they are both green.
        They also don't sell caps, thankful Amazon does.

    3. Expert Member
      BILL WICHERS | | #17

      If it’s just temporary, you could use furring strips as battens to hold the polyiso sheets up until you are ready to permanently fasten them. This would limit the number of temporary fasteners you’d need.

      You can get long screws of reasonable (less than 1/4” diameter), but they’re usually a special order item. I know Spax makes some, I’m sure there are other options too.


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