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Is that black fibre sheathing structural

rickjl | Posted in Construction Techniques on April 23, 2008 08:57am

It is black 1/2 inch thick and black tar on each side.  Stapled almost every 4 inches.  Probably instlalled mid 70’s.

Can you remove 12″ masonite nailed top and bottom and replace with blind nailed Hardi Plank?

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  1. Piffin | Apr 23, 2008 01:04pm | #1

    I have not seen it as you describe with tar ON both sides. I am familiar with Homasote INMPREGNATED so the tar runs all the way thru it.

    The Homasote is not structural. 1x4's were generally let in to the framing for wind rack resistance. You need to nail new siding where the studs are.

    Depending on your other exterior trim details, and your climate, I would consider adding a sheet of Thermax and furring to get more insulation and a rain screen under the siding.

     

     

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      BossHog | Apr 23, 2008 04:47pm | #6

      "1x4's were generally let in to the framing for wind rack resistance."

      I've heard of that, but have never seen it done. Around here they used to do plywood at all corners when that stuff was used.
      He who chases too much shall catch none [Milton T. Sikhakhane]

  2. Danno | Apr 23, 2008 02:46pm | #2

    Maybe it's Cellotex--was the customary sheathing around here in the '50's and 60's. As far as I know, it is not structural--you could easily break it with bare hands. I sure wouldn't trust it to provide much structural strength.

  3. BoJangles | Apr 23, 2008 03:02pm | #3

    Sounds like Cellotex.  Definitely not structural.  When we install 12" cement board, we always nail top and bottom. 

  4. Marson | Apr 23, 2008 03:19pm | #4

    There are a number of different brands. Biltrite, celotex, etc. We call it "beaver board". It's hard to say much definite without knowing exactly what brand you have.

    I'm going to disagree here and say yes, it is structural (or at least it can be, depending on the brand). I sheathed a house in it just last winter, per the architect and owner's request. We had to nail it every six inches, and edge nail it every 3 inches. Never will I agree to that again without an upcharge, but it did work. It is a recycled product, so it is green, whatever the heck that means these days.

    I would think you would be fine putting fiber cement on it. You will definitely have to hit the studs, and will need backing every place you need to nail. No cheating and nailing into the sheathing. The project I did last winter, we firred it out with 1x4s.

    Like another poster, I'm always a fan of exterior foam, but since you have 1/2-3/4" of something with zero nail holding ability already, you would be limited in how much thickness of foam you could add.

  5. DanH | Apr 23, 2008 04:43pm | #5

    Yeah, your standard beaver board, while nowhere near as strong as plywood, is remarkably tough and is sufficient to resist racking in "average" conditions if stapled every 4 inches or so. (Never heard of nailing it.)

    The face-nailed hardboard siding is providing very little racking resistance. Replacing it with blind-nailed fiber-cement should not create a structural problem. (Though I'm no fan of blind nailing due to the poorer weather resistance.)

    Consider installing a housewrap over the beaver board -- can significantly reduce air infiltration.

    What is wanted is not the will to believe, but the will to find out, which is the exact opposite. --Bertrand Russell
    1. rickjl | Apr 23, 2008 07:27pm | #7

      "Yeah, your standard beaver board, while nowhere near as strong as plywood, is remarkably tough and is sufficient to resist racking in "average" conditions "

      I may not have described it well but it sounds like this is it.  It is black front and back and some kind of brown fibre between.  You can easily break it with your hands.  So no worries.

      "Consider installing a housewrap over the beaver board -- can significantly reduce air infiltration."

      Tyvek is planned.

      1. roger g | Apr 24, 2008 12:21am | #8

        You are right, we used lots of "Tentest" in every building. It's black on both sides with a crumbly, sawdust like filler, beige in colour. You can easily break a board in half or punch a hole through it with a fist. I think even a woman could punch through it. If you had a small piece in your hand you could easily crumble it into tiny pieces.
        I came across some of that stuff just recently on Vancouver Island inside a wall and most guys didn't know what t was.
        I wouldn't think it was structural at all but in Ontario it was used on homes that were brick. In fact most homes were brick back then so maybe it didn't need to be structural. Here on Vancouver Island the stuff was behind stucco so in effect there was nothing structural in that wall other than drywall on one side and a skin of mesh and stucco outside.
        Beaver board as I remember was much harder.roger

        1. oldhand | Apr 24, 2008 03:20am | #9

          Back in the Pleistocene we called it blackboard and nailed it with 2" roof nails. Some had asphalt 2 sides, some one. When the roof was papered the house was "blacked in". Older jobs had 1x4 or 6 let in corners [now there's a PITA], later plywood corners. Saw this resurface a few years ago when OSB was expensive. Seems like it had a decent r-factor but little racking strength, zero as a nail base.  Retired until my next job.

  6. bennyd342 | Apr 24, 2008 05:58am | #10

    check and see if it is labeled as"sturdi-brace"

    if so it is rated structural though i wouldnt use it on a narrow wall such as your typical garage front...

    used to see it in the early 90's in northern illinois

     

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