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Old 01-16-2017, 08:26 PM   #1
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Double cantilever deck plans


Hey everybody. I put this free-standing deck design together and I'm looking for a sanity check. I checked the cantilever overhang span tolerance for the double 2x12 beams and 2x10 joists and I think I'm in good shape but you never know... I know I may be overbuilding it a bit but I want this thing to last a long time. The 4x4s are just rail posts that will be secured to rim and floor joists in corners, hopefully, as well as some posts for the stairs.

See anything you'd change? The stairs layout isn't final as I need to make some adjustments due to a new retaining wall I had installed. The deck will be installed on an incline.

Brad
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Old 01-16-2017, 09:06 PM   #2
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Re: Double cantilever deck plans


What is your height from grade?

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Old 01-16-2017, 09:34 PM   #3
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Re: Double cantilever deck plans


It will be about 7' height from grade in the back (top side in the picture) and ~4' in the front. I'm open to suggestions on the best way to brace it against racking etc too.
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Old 01-16-2017, 09:51 PM   #4
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Re: Double cantilever deck plans


Just checked a chart and the joist lengths and beam sizes look okay according to the one chart I looked at but one issue you might have when you go to get a permit is the length of the Beam cantilever.
The drawing shows about 3 ft of Beam cantilever. The "rule of thumb" I use is 2 times the depth of the beam, so in the case of a 2 ply 2 x 12, the cantilever should be only 2 feet. Moving the piles out a foot would increase the beam support spacing to around 12 feet, which my chart says would be okay with 2 ply 2 x 12 beams and 2 x 10 joists @ 24 inch c/c, so it would be okay to do so. Max supported joist length of 10 feet for that layout. Again, you look okay on that as well.
I have another source to look at and will post back here if your layout fails using that design criteria.
If you want to see the chart I used, let me know by PM. Thanks.
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Old 01-16-2017, 10:26 PM   #5
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Re: Double cantilever deck plans


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Compare it to one of the prescriptive Deck Codes, eg; http://www.awc.org/pdf/codes-standar...Guide-1007.pdf

Gary
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Old 01-16-2017, 10:33 PM   #6
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Re: Double cantilever deck plans


Quote:
Originally Posted by jlhaslip View Post
Just checked a chart and the joist lengths and beam sizes look okay according to the one chart I looked at but one issue you might have when you go to get a permit is the length of the Beam cantilever.
The drawing shows about 3 ft of Beam cantilever. The "rule of thumb" I use is 2 times the depth of the beam, so in the case of a 2 ply 2 x 12, the cantilever should be only 2 feet. Moving the piles out a foot would increase the beam support spacing to around 12 feet, which my chart says would be okay with 2 ply 2 x 12 beams and 2 x 10 joists @ 24 inch c/c, so it would be okay to do so. Max supported joist length of 10 feet for that layout. Again, you look okay on that as well.
I have another source to look at and will post back here if your layout fails using that design criteria.
If you want to see the chart I used, let me know by PM. Thanks.
My figures and charts show the same thing. Experience tells me to do that as well. It'll be bouncy if you don't.
As far as rack bracing, I would corbel the top of the piles (6x6) if I need the open space under the deck. If not, I would box it in, and add lattice work underneath to keep unwanted critters and trash from getting in there.


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Old 01-16-2017, 10:46 PM   #7
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Re: Double cantilever deck plans


I won't be able to move the front side (bottom of diagram) piles outward towards unfortunately because they will already be up against the side of a retaining wall that sits a couple of feet out from the porch piers. Reinforced footings for the front 4 piles were recently installed. They extend under the wall so they're independent from it.

Perhaprs I can go with triple 2x12s for each beam instead of double. They'd sit nicely on top of the 6x6 piles that way. I can also use a ledger attachment to the 2x12 rim joist edge of my porch on the front. That would bear enough load to stabilize the extended overhang. Also the piles on the back side (top) CAN be moved back so the overhang is only 2 feet.

Thanks for the feedback on this. I'd rather get this sorted BEFORE I build it than after...

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Old 01-16-2017, 10:56 PM   #8
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Re: Double cantilever deck plans


Using the source Gary links to, I would want to increase the beams to a 3 ply 2 x 12 to increase the beam support spacing out to 12 foot.

Thanks, Gary. I was watching the Hockey game instead of searching for my copy of the Specs you posted.
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Old 01-16-2017, 11:24 PM   #9
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Re: Double cantilever deck plans


I concur...

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Old 01-17-2017, 09:20 AM   #10
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Re: Double cantilever deck plans


Ok based on y'all's feedbackc I believe this updated design will work. Now I need to get a closer look at the ledger connection component. The old 10x12 deck isn't torn down yet (but about to fall down on its own) and has a 10' ledger board, but it needs to be redone. Fortunately there is no wood rot to contend with!
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Old 01-17-2017, 01:49 PM   #11
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Re: Double cantilever deck plans


Quote:
Originally Posted by Brad_TX View Post
Ok based on y'all's feedbackc I believe this updated design will work. Now I need to get a closer look at the ledger connection component. The old 10x12 deck isn't torn down yet (but about to fall down on its own) and has a 10' ledger board, but it needs to be redone. Fortunately there is no wood rot to contend with!
I would probably add some cribbing into the floor joists in an X pattern to keep the deck square and help prevent it from racking, but everything else looks great.

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