Help! My pressure treated lumber is warping!
Recently I patted myself on the back when I completed my new pergola. Two 4x4x10 foot posts seated in nice custom concrete-anchored planter boxes, doubled 2x6x12 foot cross bars connect the posts (one on each face), and 10 2x4x12 foot slats which are anchored to the house and the cross bars (10 feet away). The slats are set upright on the 2 inch edge and travel out parallel to the ground (perpendicular to the house and the cross bars) to the cross bars. All of this was done with pressure treated lumber which was straight as an arrow when I bought it, but still damp from treatment (no dried lumber was available). So...my problem is that the slats are warping, bowing, and driving me crazy! I replaced a few once I noticed the warping, but soon I realized that ALL of them are warped. The retailer told me a refund was out of the question since I cut the lumber already and getting pre-dried pressure treated lumber is very costly, so I'd like to avoid that. Here's the question. Is the lumber ALWAYS going to warp over such a long distance, or is it possible to anchor the slats (with perpendicular cross members) to prevent them from warping? I'd appreciate your advice and thanks for tolerating the long winded message. You free-spanned 2X4's TEN FEET?? Yes, they are going to warp and sag. Going to 2X6's, 2X8's, etc. will result in the same problem. You can reduce the amount of warp and sag by adding mid-span blocking, but you won't eliminate it. Only solution that I know will work would be to use roll-formed aluminum patio cover parts. You'll need to find a patio contractor and to get them. Tell me where you are and I will see if I can help you locate somebody. Even pressure-treated lumber stamped KDAT (kiln-dried-after- treatment to 19% moisture level) would warp with that span. Pressure-treated will usually warp worse than untreated lumber when the CCA begins to dry out and crystalize in the white cells of the wood, anyway. lefty, as usual, has the best solutions for you at this point. Good Luck! Mike I have a shade/decorative unit i built over top a 10 x 12 deck out of 2x6s and 1x2s . the 2x6s free span roughly 9 feet 10 or so inches without any sag or problems with a 1 foot 4 inch i think cantilever off the ends at an angled cut and its been in place for over a year. the top is connected with 1x2s crisscrossing the 2 xs at 2 foot intervals.. then perpindicular 1x2s on 1 foot centers between the 2 foot centered 2x6s .. The cross bracing of the top helps the whole roof act as one unit and resist sagging or bowing. If you are looking for a semi cheaper fix... why not add mid span support to your pergola? Hope this helps--Josh Josh1, I'm not quite sure I am visualizing how you constructed your shade when you talk about criss-cossing 2x6's and the relation of the 1x2's to the structure. And, Lefty, I haven't heard back from you about mid-span blocking or other alternatives, so let me see if I can depict this a little better. Flower box bases, about 10 feet apart and 10 feet from the house, hold the 4x4 posts upright with concrete. Spanning between the tops of the posts are 2 - 2x6x12s, creating a double 'header.' Attached to the house by brackets are the 2x4x10s. The 2x4x10s travel out parallel to the ground and rest on the double header, attached to it with brackets. Here is a crude drawing of my pergola: House | ------------------------------ H |----------------------------- | | | | | | | | | | | o | ||| | | | | | | | | | | | u | | | | | | | | | | | | | s | | | | | | | | | | | | | e | | | | | | | | | | | | | | | =:=============:= | | | | | | | | | | | | | | H|H ================= TOP view SIDE view 2x4x10s are the strings flower box/base is the H|Hs of |s 2x4x10 is the string of -s 2x6x12 'header' is the 4x4 post is the string of |s string of =s 2x6x12 'header' is the ||| 4x4 posts are the :s | | | | | | | | | | ================ || || || || || || 2x4x10s are the |s || || 2x6x12 'header' is the string of =s || || 4x4 posts are the strings of ||s HH HH flower box/bases are the HHs FRONT view The warping and twisting that is going on in my pergola is evident from the top view or looking end-on the 2x4x10s. They are not sagging toward the ground at all! I don't think adding small interspanning 2x4 chunk blocking parallel to the 'header' between the 2x4x10s would work very well. Trying to line them up so they look like one continuous piece while looking at it from below would end up looking very bad. My carpentry skills are OK, but not great and the tools I have to work with are very basic and consist of table saw/circular saw, hammer, nails, level, etc... So...my proposed solution was to replace the 2x4x10s with new ones. To prevent warping and twisting, I would tie them to eachother perpendicularly with a layer of 1x2s (2 inch side attached to the 2x4x10s) to create a grid along the tops of the 2x4x10s, parallel to the 'header' and spaced about the same as the 2x4x10s which would look something like this... __________________ | | | | | | | | | | ================ || || || || 1x2 is the string of _ || || 2x4x10s are the |s || || 2x6x12 'header' is the string of =s || || 4x4 posts are the strings of ||s HH HH flower box/bases are the HHs FRONT view Lefty, Josh1, anyone, what do you think? I hope the crude graphics (if they come out right) can explain this better than words, if not I can send you some pictures via email if need be. Please let me know what you think or any other advice you might have. Thanks a bunch! E-mail me the pictures (PM button at the bottom of this post). I think I understand your graphics, but I want to make sure. Hi again Im semi following your drawings but my ? is you are planning to put the 1x2 with the 1 inch side horizontal? So you would be screwing into only 3/4 of an inch of wood.. maybe go with 2x2s in that case if you dont want them on the flat Actually if your boards are not bowing and are twisted .. you could simply make lay out lines on the 1x2s or 2x2s and use galv deck screws and a few clamps to pull it all into position or simply do one at a time pulling it to the line and screwing it down no need to replace all the 2x4x10s. Just my thoughts. i tried attatching a drawing of how mine is done.. not to scale or anything the red lines are 2x6x10 the blue lines are 1x2x? i dont recall length precisely the green lines are 1x2x ? the black lines are 2x6x 8 headers with 1/2 cdx between on top 4x4 posts Hope this helps --Josh also about the 2x4 blocking it isnt as hard as you might think.. you snap a chalk line down the middle and then install one block.. and offset the next one by 1 1/2 inch so you can nail/ screw it in.. and then the next one is on the alternating sides of the chalk line.. its just like installing blocking in a subfloor if youve ever done that ..wouldnt look bad .. but its a personal choice of course.. Hope this helps---Josh
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