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Thread: Pressure Treated Decking Lumber

  1. #1

    Pressure Treated Decking Lumber

    I'm going to be replacing the decking on my daughter's deck. It currently has pressure treated 5/4" decking and will be replacing with the same. When picking out boards at the "Big Box" retailers, is there a way to examine a given board to determine its likelihood of warping, twisting, cupping etc. as it dries out? Does the end grain pattern provide any clues?
    The deck is 16 ft long with 12 ft joists. I'd like to buy 16 ft boards but transporting will be a bit of a problem. I'm concerned about the joints using two 8 ft boards per row. Am I overthinking it?
    BTW, I called a couple of places to price kiln dried PT boards and they were quadruple what HD charges for the "wet" stuff !

  2. #2
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    There really isn't a way to prevent deck boards from doing any or all of the things you listed, except to use one of the non-food decking products. the problem stems from the fact that wood will absorb water and when the sun comes out, the top surfaces get baked and dried out while the under side stays damp. You can reduce the cupping by placing the bark side up.
    Lee Schierer
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  3. #3
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    Get KDAT lumber (kiln dried after treatment) from a real lumberyard. If it's going to warp, to a considerable extent, it will already have done it. They will deliver it to you. Much lighter and easier to work with as well, more predictable gaps between boards after it equilibrates.

  4. #4
    I could only find KDAT at 2 yards and they wanted $45 / 16' stick vs $11 at HD. Add $100 delivery charge and I think I'd be better off tossing the ones that are ugly after drying.

    Quote Originally Posted by roger wiegand View Post
    Get KDAT lumber (kiln dried after treatment) from a real lumberyard. If it's going to warp, to a considerable extent, it will already have done it. They will deliver it to you. Much lighter and easier to work with as well, more predictable gaps between boards after it equilibrates.

  5. #5
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    Just double up joints were needed and split the 16. Criss cross

    I ran into the same problem buying too long of boards needed. When done I ran a belt sander across the seams and slick as

  6. #6
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    Shorter boards stand a better chance of staying straighter.

    KDAT is not a magic bullet for lumber staying straight , flat ect... It GREATLY increases the odds , but it's not a guarantee.

    Butt joints (w/8ft.) is an aesthetic issue more than an engineering one. Be sure to re-treat any / ALL cut ends before installing and use joist tape to protect the framing.

  7. #7
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    Last year I rebuilt the south porch and added a north porch here to replace one that had been torn off more than 50 years ago. The house is 16 feet wide so the porches are too, and I bought 16' lumber from a local lumberyard chain. They delivered for $50 from about 35 miles away, and I was buying a lot more than I could get in one trip on my little trailer. I like the full length pieces, and I find that if I put two screws in each joist, and the joists are 16" on center the boards stay quite flat enough to feel flat when walking across them.

  8. #8
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    When I did my deck, where a joint in the deck boards was needed I doubled the joists such that they were not tight together and the deck boards slightly over-hanged the joists with a gap between them. Idea was to avoid the major cause of rot which is moisture collection and not being able to dry out; the end grain is more of a problem. Modern PT is not as anti-rot effective as the old PT.

  9. #9
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    If the budget allows think about using Trex or one of the composites. Trex stays looking good for many years and never needs to be stained. Another thing that prolongs the life of a deck is to cover the top of the joists with joist tape. Flashing along the rim at the house is also important.
    I remove the old decking by cutting it all up in place rather than trying to take up whole boards.

    image.jpg
    Last edited by Maurice Mcmurry; 02-27-2024 at 9:37 AM.
    Best Regards, Maurice

  10. #10
    Doesn't your HD rent trucks? Buy longer boards and haul them in rented truck. As far as cupping, generally longer boards are cut from lower section of tree, which have less knots and less prone to cupping.

  11. #11
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    Climate? For something like this I try to buy the wood in summer about one month before the project starts. Stack and sticker it to dry a bit. Buy 10% more then needed. Return badly warped and twisted lumber to the store.
    Bill D

  12. #12
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    Im all for trex but it will increase the budget. Make sure you crown your boards so that if it does anything it will have to warp past dead flat before warping. This also will allow water to run off. And as always avoid big box wood.

  13. #13
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    Just look at the grain and leave the ones where the grain runs back and forth across the top. I do the same when picking any lumber for framing or anything else. If the grain looks like a dogs hind leg on top of the board, that one is going to move.

    I've built decks and docks using that 5/4 treated lumber. With joists on 16" centers, I alternate the screws from one side to the other on alternate joists. If any of the ends start to twist up after a month or two, those get another screw before it completely dries.

    I like the Deckmate screws with T25 heads.

    When I was building new houses, I used to order a whole bundle of No.1 grade decking boards. No one ever kept that in stock, but it was available if you bought a whole bundle.

  14. #14
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    I'll second Maurice's recommendation of joist tape - I wish I'd used it when I built my deck about 20 years ago but so far so good anyway. I also used Trex decking which like the rest has been down the 20 years; it's faded but otherwise still in great physical condition. Both the cedar and PT previous decking was shorter lived and the Trex is still going.
    I've heard of people using roofing ice-guard type product cut into strips for covering joist tops.

  15. #15
    Climate is the most impostant IMO
    Where are you and the deck located.

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