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I ordered lumber from Lowes for building deck beams, but now I realize after putting up the beam that while they are all level, the boards are of slightly different widths.

Of the 2x10 boards I had for both the ledger and the beams thus far, everything tells me that they should be 9 1/4" actual, when in reality they are mostly 9 1/2" and some of the beam boards are 9 3/8" actual.

Is this normal for weather treated wood to swell a bit after it is planed and cut? Any ideas on how to get the joists to set evenly on the beams now? I figured if a beam is slightly too high then I could notch the top of the beam for the joist, but if it is too low by a 1/4" perhaps that I might have to shim it?

This is sort of throwing everything I know for a loop. When I get dimensional lumber then it should all be of uniform width. Apparently this is not true anymore.

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    I might be convinced boards swelled 1/8" but not 1/4". It is what it is though. If you select boards by width you should be able to effect a layout where the variations need little correction. If you must notch, notch the joist, not the beam, and do not make an inside corner notch, it creates a stress riser, just curve the cut off.
    – bcworkz
    Commented Sep 2, 2013 at 18:26
  • @bcworkz Thanks for the advice going forward, as I am carefully lining up and numbering my joists now to try and get them as level-ish as possible. What I don't understand is that if I round the corners of the joist notch, wouldn't that create stress points on the corners of the higher beam? The beams are doubled but on either side of the post so the parallel beams are not touching.
    – maple_shaft
    Commented Sep 3, 2013 at 1:48
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    The main thing is joists carry less total load than beams, so if you are to compromise any structure, it should be the one with less load. The biggest problem in notching is over cutting the cross cut and the very abrupt change in fiber length. It may be best to simply grind off the excess material at supports with a very coarse gritted belt sander running parallel to grain, which tends to make an ideal profile automatically.
    – bcworkz
    Commented Sep 3, 2013 at 19:51

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Reorder the beams so they are installed from shortest to tallest, with same heights together in sequence. I would place the tallest next to the building.

With a little luck, a board across them will create a straight line. If it does not, how much variation could there be? 1/16th inch? 1/32nd? If you are blessed with perfect climate which will not distort the lumber's dimensions, then maybe some sliver shims are called for. Otherwise, prohibit your guests from laying down and gazing across the decking.

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Not only are you dealing with pressure treated lumber but you are also dealing with the big boxes leaving this stuff out in the rain. Basically a 1/4" variance is about 3%.

This seemed about normal to me but I double checked the internets and Purdue says that it can be even higher.

So your dryer pieces could be at 9 1/4 and the wettest at 9 1/2... I have personally gone through this a lot at the big stores. They don't care. But you can dig to the bottom of the stack. As you get further in the stack the wood is more protected, more uniform, and straighter.

Basically in this situation you need to take anything back more than 1/8 inch at most and get new boards.

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  • Thank you for the information... I unfortunately don't have access to a truck where that is easy to do. I had to have it delivered which meant I was at their mercy in regards to selection. I guess I was wondering how it can be dealt with, since the beams are already cut and bolted in place.
    – maple_shaft
    Commented Sep 3, 2013 at 9:32
  • After it is down it is a waiting game. You need to get them dried out. Maybe you do nothing! If you still see issues after I see a lot of sanding in your future.
    – DMoore
    Commented Sep 3, 2013 at 15:28

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