Post/beam connection for low deck

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Old 04-10-05, 10:00 AM
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Post/beam connection for low deck

I'm tearing out an old free-standing deck and putting in a new attached deck, about 18' deep and 20' wide. The top of the decking will be about 20-24" above grade. I plan on using 2x8 joists and 4x8 beams. The joists will rest on top of the beams. If I mount the beams on top of the posts, that will mean that the posts would only be 4-8" long. I have read that such short posts can split and break.

My local building code suggests mounting the beams by making 3/4" notches on each side of the 4x4 post and sandwiching the post beween 2x8 beams. This would then mean the posts will be 12-16" long. Would this be preferable instead of the short posts, or is there even a better way?

Thanks!
 

Last edited by jcs; 04-10-05 at 10:12 AM.
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Old 04-10-05, 03:24 PM
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posts 6-8 "inches"?

need a little more informatin. are these posts supporting your deck? what do they sit on? aren't you burying them in the ground below the frost line? that would be 42" , which is the code requirement in most states. if the deck is attached to the house, these code rules apply. if it were free standing, then it could sit on the ground.

With 18 feet of joists, i'd be running a beam at two places. my choice for a beam would be two 2x8s with the post sandwiched between them and bolted with carraige bolts.

not sure if this is on target for your deck. if not, give me more info.
 
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Old 04-10-05, 04:47 PM
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jcs,

With an 18' projection on the attached deck, you'll need 2 beams. Why not use 4X6 beams and 2X6 joists?? That would make your posts 4" longer than what a 4X8 beam and 2X8 joists will allow.

jay_myself,

We don't know where jcs is, so we have no clue (yet) if frost is an issue for him or not. If it's not an issue, then his footings will probably only be 12" to 16" deep and 16" square. If he sets a post base (Simpson PB44 or similar) in the footing when he pours it, the post will then be attached to the post base, and be kept slightly above the concrete of the footing so that it doesn't rot.
 
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Old 04-11-05, 08:38 AM
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More information

Originally Posted by lefty
jcs,

With an 18' projection on the attached deck, you'll need 2 beams. Why not use 4X6 beams and 2X6 joists?? That would make your posts 4" longer than what a 4X8 beam and 2X8 joists will allow.

jay_myself,

We don't know where jcs is, so we have no clue (yet) if frost is an issue for him or not. If it's not an issue, then his footings will probably only be 12" to 16" deep and 16" square. If he sets a post base (Simpson PB44 or similar) in the footing when he pours it, the post will then be attached to the post base, and be kept slightly above the concrete of the footing so that it doesn't rot.
Thanks guys for your replies.

Yes, definitely I'll run two beams for this deck. The posts will be fastened on top of concrete piers that go to 42" depth (local code). I'm assuming the tops of the concrete piers will be around 2" above grade (to keep the wood posts from rotting). Using 2x8's and 4x8's, that's how I came up with the figure of posts being 4" to 8" long.

I will have a contractor come in and dig the holes and pour the concrete, so I'll avoid that hard work

Lefty, will 4x6's and 2x6's offer enough strength for this size deck (40 lb per sq ft active load)? The joist spans will be about 9 feet and the beam spans about 6-7 feet. Unless I read the span table wrong I thought I at least needed 8" nominal lumber. Please let me know if I'm wrong about that.

Also, if I'm notching posts, it seems wiser to go with 6x6's instead of 4x4's. Thoughts? If using 6x6's, can I still use 8" diameter piers or would I need to go to 10"?

Thanks again! This is a big help.
 
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Old 04-11-05, 07:36 PM
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same problem

Hey everyone! I currently am in the same situation, short deck beams I am using 2x6 joists with beams 8 ft. apart. My deck posts would 10" high off the concrete piers w/ sandwiched 2x8 beams, attached to the posts w/ carriage bolts. My only other thought to provide better strength would be to set the posts in concrete 42" below grade and 10 " above grade. So, would you guys set the posts in concrete or would you go with the 10" posts with sandwiched beams? Should I even be concerned using 10" posts? Thanks for all your help!!
 
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Old 04-12-05, 11:51 AM
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jcs,

You didn't misread the span tables. You will need minimum 2X8 joists and 4X8 beams at the spans you are talking about. And you'll need piers that are at least 10" diameter.

illenderle,

Don't bury the wood. Set a post base (Simpson PB44, CB44, or similar) in the wet concrete, and, once the concrete has cured for a few days, you'll attach the posts to those bases. And you crown the top of the concrete so water can't stand on it, and you make sure the plate of the post base is sitting on the concrete, not buried in it.
 
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Old 04-12-05, 05:02 PM
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Originally Posted by lefty
jcs,

You didn't misread the span tables. You will need minimum 2X8 joists and 4X8 beams at the spans you are talking about. And you'll need piers that are at least 10" diameter.
Hi Lefty,

Thanks! I'll go with longer 6x6 notched posts instead of the short 4x4's then, and the 2x8's and 4x8's. I appreciate the help!

JS
 
 

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