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Trex as a plate on concrete?

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  • Trex as a plate on concrete?

    I'm enclosing a large carport and it will become MY SHOP!! So here's the deal: The roof overhang is huge (4') and even in the worst Hawaii rains, the floor of the carport has never been wet. The very substantial roof is supported on seven 8 x 8 posts, so the walls I need to build will go between the posts and are non-bearing. I'm looking for some feedback on the idea of using a piece of Trex or similar solid decking under the sole plate, and then just bolting down the walls in the usual manner. Reason for the synthetic under the wood is just in case there is ever any water there. I just don't want to have to place concrete curbs under those walls . . .

    And no, there will be no building permits involved here.

    Unanswered Questions
    are far less dangerous
    than Unquestioned Answers.

  • #2
    how about a course of concrete block with all thread bolted through and secured to the slab? an 8 x 8 x 16'' block is easy to layout. then you can fill the block with concrete and have a solid base.

    i think you need 6'' above the slab for wood contact

    phoebe it is


    • #3
      Round these parts pressure treated lumber is required for the soleplate.
      Any termite concerns over there?
      "Did you put the yellow key in the switch?" TOD 01/09/06


      • #4
        Follow Plumber Rick. On Long Island the sole plate would be ACQ treated lumber bolted to the foundation. It must be 8" above grade. If you do put a course of block down then you can add a termite sheild and you should be all set.


        • #5
          Why not use 4" block since the wall is non-bearing?
          "It's a table saw, do you know where your fingers are?" Bob D. 2006


          1/20/2017 - The Beginning of a new Error


          • #6
            Didn't want to mess with concrete/blocks . . .

            Here, houses are built every day right on concrete slabs, using a strip of roofing felt under the sole plate. Water is kept away from the framing (it's all treated wood in Hawaii) by way of the siding, which overlaps the slab an inch or so. And yes, the wood needs to be 8" (I think it's 8") off GRADE. What I have here is a huge concrete slab that extends like 8 ft from where the new wall will be, and there's a 4' roof overhang above that. The slab slopes slightly away from the center of the carport, so no water ever accumulates near where the wall will be. And there's no dirt within ten feet of the new wall location.

            Darn, I thought I had a cool idea here, but it's not getting a very enthusiastic response. I wanted to keep it simple. The proposed walls are nothing more than to keep out the weather. They have no structural significance at all. Does that make a difference?
            Unanswered Questions
            are far less dangerous
            than Unquestioned Answers.


            • #7
              You already said you weren't getting permits. Therefore, your question becomes, what do you want to live with? I'm sure HI has it's share of wood-eatin little pests. Do you want to feed them and have to rebuild the wall in a couple years? Do you want to offer them a buffet table that leads to your house?

              I don't mean to belittle your idea at all. Please don't take my terse reply that way. It's hard on forums to get through that it's meant with humor and some little nudge towards reality. I think that you need to at least go with pressure-treated for the sole plate. Completely up to you, however.

              The other thing is Trex wouldn't be my choice for anything that's going to carrying a load. IMO the material is too susceptible to "denting", or compressing under the studs. I'm not a materials expert by any means. I've just worked with Trex before and while I love it for decking boards (non-load-bearing), I wouldn't want to support the deck with em!
              I put it all back together better than before. There\'s lots of leftover parts.


              • #8
                Termites in Hawaii, nah, My Dad lived in Haliewa. Why not go with a PT 4X6 bolted to the slab with silicone under it, make the sole plate PT 2X4 and let er roll. Get a local pest control company to take care of the termites with perimeter treatment outside, and drill the slab and inject where the slab is up against the exsiting foundation. Keep all wood elevated in the shop, and clean up all the dust to keep from "baiting" the rascals.
                Only a surfer knows the feeling. Billabong ca. 1985 or so