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I'm working on a deck that will involve two 10ft wooden beams across three wooden posts. One of the posts will be in the middle of the two beams. What is the proper method for joining the beams to the post?

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Just to clarify, is this a 20ft span with two 10ft beams, and a post in the middle that will support the ends of the two 10ft beams? If so, why not just make a 20ft beam? – Eric Petroelje Aug 25 '10 at 18:02
Easier to get the 10ft lengths – awithrow Aug 25 '10 at 18:06
@awithrow - if you are building a beam from 2x wood, you can build a 20ft beam by staggering the 2x's then gluing and nailing them together. So, for example, one side would be 2 10' boards end to end and the other side would be a 5' board, a 10' board and another 5' board. You can sandwich some 1/2" plywood between them as well to make it an even 3.5" wide. – Eric Petroelje Aug 25 '10 at 19:43
I'll have to check to see if that meets code requirements in my area, but I don't think it does. – awithrow Aug 25 '10 at 19:46
@Mike - yes, he would certainly need a center post. But building one big beam avoids the problem of having an iffy "butt joint" where the two beams meet on the center post. – Eric Petroelje Aug 25 '10 at 20:35
up vote 6 down vote accepted

Typically you would have the beam sit on top of the posts and use a post tie like this one:

post tie

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What, you're not supposed to bolt through those holes? I think we might've used 'em for lags when building my neighbor's swing set / play area. – Joe Aug 25 '10 at 18:00
@Joe - I guess not, but can't see why it would hurt (although it's probably unnecessary) – Eric Petroelje Aug 25 '10 at 18:06
Would the two beams simply form a butt joint in the middle of the tie? – awithrow Aug 25 '10 at 19:50
@awithrow : no, you'd want to overlap the post fully with each beam, if possible, so the load's better transfered down the post. (assuming they're load bearing; if it's just a pergola or similar, you could probably butt them) – Joe Aug 25 '10 at 20:25
@awithrow - yes, seems they would have to (which is why I was suggesting building a single 20ft beam). – Eric Petroelje Aug 25 '10 at 20:39

If your posts are large enough (e.g. 6x6), you can notch the top of the post to accept the beams, then bolt through the beams with carriage bolts. That way, all that's visible are the rounded heads of the carriage bolts, which may be important if your beam is exposed.

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The best choice is to use a post cap. If you are using pressure-treated wood, it will need to be decay-resistant.

If you are using the Simpson connectors, the PC or EPC series is your friend. It has enough length to join the two beams securely and to attach to the post well.

They also make an architectural series that is thick and black and looks nice, but they are much more expensive.

You can download the Simpson catalog for more details.

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