3

So, I had a load of wood delivered a few days ago for a deck build. With the beams, I have one board that is about 1/4" smaller in width than the others. What is the right way to deal with this?

A) Center it with the other 2x10 that I'm doubling it up with, leaving 1/8" top and bottom (guessing that it is newer wood, and will shrink equally)

B) Level the top of the double beam, leaving a 1/4" gap against the post. Fill in that gap with a 1/4 shim.

C) Same as B, but level the base - but no shimming on top. The joists will simply be "sitting" on one 2x10 instead of on both of them.

8
  • @JimStewart, beams must rest on posts, and shims are a valid means of doing that. They can't rely on the shear strength of fasteners to carry them. Disaster will almost certainly not strike, but that's how code is written. That said, I think you misunderstood option C, which has the beams flush on the bottom. They'd both rest on the post.
    – isherwood
    May 27 at 20:43
  • To add to this - I have about 10 pieces of 2x10. Only one is "Short" - the other 9 are all the same. I feel that ripping 9 2x10's to match the one isn't quite the right plan...
    – Akshue
    May 27 at 21:09
  • @isherwood - Chicago code (PDF) (precisely where disaster did strike) requires minimum two 5/8" through bolts ("sufficient to transfer load") and 1/2" thick, 4" x 8" ell brackets for ledger boards; nothing rests on the top of a post except more posts utilizing extremely specific splices and more bolts. - So it wouldn't matter to me that it's an 1/8" too short, I just have to drop $500 on steel every time I build a deck.
    – Mazura
    May 28 at 4:51
  • I'm not sure how we got on ledgers. That's a rather different situation.
    – isherwood
    May 28 at 12:35
  • Page 25. "Edge Beam" (aka, ledger) Uses four bolts and one bracket per post. An actual 'beam' (instead of a doubled up ledger... "the other 2x10 that I'm doubling it up with") would sit in a notch on a post with tie plates, page 27. If anything, the posts are ~4' too short... how are you going to do the railing?
    – Mazura
    May 28 at 22:00
3

Are your posts set in place already ? If not, leave one row of posts slightly tall, up to an inch above the level set by all the others. Perhaps a middle row so its not visible.

When you lay out the deck beams, make them all the same height but that one row. Then top them with a cut that looks like

+------
|     |
|     +-----+
|           |

Essentially its leaving the shim allowance in the post rather than adding a separate piece.

When done it will look like this from an end view (exaggerated)

+-----+-----+
|     |     |
|     |     |
+------     |
|     |     |
|     +-----+
|           |

You might want to take extra moisture precautions on this row - prepaint the cut top before installing beams.

12

I don't like any of the A-C options presented here, the beam is a very important structural component and incorrect beam installations can compromise the entire deck. Shims, shortcuts and hoping for shrinkage are inappropriate. I would either:

D) Return/exchange the bad board for one that is proper size.

E) Trim the larger beam member to the same width (height, as installed) and adjust the post-beam notch or bracket to compensate for the slight decrease.

Of these two options, I favor option D but with sky-high lumber prices and low availability now (Summer 2021) that might be difficult.

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  • There's usually plenty of overhead designed into deck beams that there's really no failure risk with any of the options being discussed. I agree that your option E is probably the best bet.
    – isherwood
    May 27 at 20:45
  • +1 for option E) May 28 at 19:43
3

C would probably be fine, but I'd go with none of the above.

Rip down (or just notch for posts) the larger boards to match the height of the smaller. Make them flush on top, which is the important outcome since either joists or decking rest there, depending on your framing design.

It's worth mentioning that the smaller board isn't "bad". It's a matter of swelling due to the immense amount of moisture pumped in during pressure-treatment. PT lumber is always larger than dry lumber, and the amount varies. This is very common and you just have to work with it.

1
  • I like the notch right at the post idea, you still get all of the span strength that way. If it's truly 1/4" wider that may look a little "off" but I'd rather have that than shims or gaps any day. May 27 at 20:59
0

This is probably overkill, but it would allow you to use the existing board.

Go buy another board of the same width. No more than 6 feet in length (a scrap piece 2-3 feet long should work if you have one). You'll also want two galvanized bolts (4 inches minimum), two nuts, 4 washers and some exterior construction adhesive. Put your new board in the middle (where it's less noticeable) and then

  1. Put construction adhesive on the new board and glue it to the short board, making sure your new board reaches the end of your cross braces (wouldn't hurt to add a 3" deck screw or two to hold it together)
  2. Drill holes for your bolts squarely in the middle (top to bottom) and add your bolts and washers, then tighten

This process is called sistering, and it allows the other board to help where this board is not long enough. Again, probably overkill, but it's certainly an option (with the price of wood high, having a scrap piece already would mean about $10 or so in other supplies).

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