New deck posts

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Christopher
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New deck posts

Post by Christopher » Wed Aug 09, 2017 1:42 pm

I have torn down the old rotten deck on our new house, and am planning for a new one. However, there is one issues I am unsure of. The old deck was approx 28 l x 18 w x 10' h, and was cantilevered approx 6ft over the original supporting posts, which did not seem safe. those posts are steel and properly footed through a concrete slab that was poured after the deck was built. The slab was attached to the foundation of the house and appears to have not moved at all in its 30+ years. We would like to maintain the original size of the deck, meaning I would need to install more support posts on the existing slab about 5' past the original posts.

So, My question is, if I used 3 4x4 posts, do I need to dig through the concrete to create new footings for the posts, or can I just use brackets and bolt the posts to the existing slab?
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A. Spruce
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Re: New deck posts

Post by A. Spruce » Wed Aug 09, 2017 2:10 pm

Since the steel posts will carry most of the weight, I would attach the posts to the slab with metal brackets. You want the kind with a shoe in the bottom to keep the post up out of the moisture.
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DanM
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Re: New deck posts

Post by DanM » Wed Aug 09, 2017 2:20 pm

Well it's quite possible you won't even need new posts. It's hard to tell exactly from the pics, but if your new deck is going to be right above the bricks you could simply lag screw a ledger board to the exterior wall studs and/or rim board. Just make sure you aren't going to be sinking the lag screws into any wires in the studs first!

If that isn't possible, for me it would depend how thick the slab is. If it's 6" or more it would probably be fine to simply drill a few holes for brackets and throw some 4x4's in there for additional support. As with most things though you're best bet for that is to double check local codes and talk to an inspector/municipal official first to make sure it's acceptable.

Christopher
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Re: New deck posts

Post by Christopher » Wed Aug 09, 2017 5:14 pm

Great, thanks for the input. I'll just bolt the posts to the pad using a bracket. I know the posts won't hold much weight, but it makes me feel better than having an oversized cantilever. Thanks for the advice!

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A. Spruce
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Re: New deck posts

Post by A. Spruce » Wed Aug 09, 2017 6:30 pm

The maximum cantilever allowed is 1/3 the length of the member, which is roughly what you had, according to the measurements provided. As long as the deck wasn't spongy, there is no need for the additional posts.
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Shannon
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Re: New deck posts

Post by Shannon » Thu Aug 10, 2017 8:11 am

A. Spruce wrote:
Wed Aug 09, 2017 6:30 pm
The maximum cantilever allowed is 1/3 the length of the member, which is roughly what you had, according to the measurements provided. As long as the deck wasn't spongy, there is no need for the additional posts.
Wow 1/3 the length of the member ? Are you sure? That would mean even a 2x4 12 feet long could cantilever by 4'! You would never catch me on that deck :?
I had a look in my code book and there is really no reference to cantilever distances on floors for decks,balconies,or mezzanines with no exterior wall load that I could find.

My suggestion is 1/4 of joist span up to a maximum of 3 feet for 2x6,2x8,2x10 joists spaced at 16" O.C. to 24" O.C.

I know some of the problem with deck cantilevers in my area is people use to enclose these decks over time and add a roof and eventually some of them ended up being additions. (without permits of course) Now they had a load on the cantilever especially in winter with snow ,that caused structural issues and sometimes failures. These failures could be fatal even at 1 foot off the ground let alone even higher .

I'm not saying you are wrong Spruce but 1/3 the length of the member could be dangerous under some conditions. Guys like you and I can look at a figure and situation and basically know if it will work and be safe but most DIYers do not have the experience of or time spent in the trade.Even in this case I would not take a chance on 6' cantilever, that gives to much room to set up a table full of people all sitting at or out past the beam or standing out at the far end of the deck. Even if the joists are attached very well at the ledger there is a lot of pressure on that connection IMO. :D
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A. Spruce
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Re: New deck posts

Post by A. Spruce » Thu Aug 10, 2017 11:38 am

Shannon wrote:
Thu Aug 10, 2017 8:11 am
Wow 1/3 the length of the member ? Are you sure? That would mean even a 2x4 12 feet long could cantilever by 4'! You would never catch me on that deck :?
It's been too long since this info was acquired to be able to cite the source, though it was reputable at the time. I'm with you, I wouldn't want that much of a cantilever, without the framing being substantial, even then it could be questionable depending on the planned use of the structure.
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Shannon
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Re: New deck posts

Post by Shannon » Thu Aug 10, 2017 12:13 pm

A. Spruce wrote:
Thu Aug 10, 2017 11:38 am
Shannon wrote:
Thu Aug 10, 2017 8:11 am
Wow 1/3 the length of the member ? Are you sure? That would mean even a 2x4 12 feet long could cantilever by 4'! You would never catch me on that deck :?
It's been too long since this info was acquired to be able to cite the source, though it was reputable at the time. I'm with you, I wouldn't want that much of a cantilever, without the framing being substantial, even then it could be questionable depending on the planned use of the structure.
Not bust'n your balls, just was suprised by the figure.
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A. Spruce
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Re: New deck posts

Post by A. Spruce » Thu Aug 10, 2017 12:23 pm

Oh, sure, you say that now! :cry: :mrgreen: :lol:
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Re: New deck posts

Post by A. Spruce » Thu Aug 10, 2017 9:59 pm

YOu got me curious, so I did an very quick Google search on "cantilever codes" and came up with this:

Beams shall be permitted to cantilever at each end up to one-fourth of the actual beam span. Source

Maximum allowable overhang cannot exceed 1/4 of the actual main sapn. Source

I think where I might have been tripped up slightly is maybe the ambiguity of "beam span" over "beam length". Span is from attachment point to attachment point (ledger to support post ), where as length is from one end of a board to the other.

Do not, by any means, take this as a definitive answer, more research would be recommended. The best place to start would be your local building department, because it doesn't matter what the rest of the world does, it only matters what is allowed in your own jurisdiction. 8-)
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Shannon
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Re: New deck posts

Post by Shannon » Thu Aug 10, 2017 10:45 pm

A. Spruce wrote:
Thu Aug 10, 2017 9:59 pm
YOu got me curious, so I did an very quick Google search on "cantilever codes" and came up with this:

Beams shall be permitted to cantilever at each end up to one-fourth of the actual beam span. Source

Maximum allowable overhang cannot exceed 1/4 of the actual main sapn. Source

I think where I might have been tripped up slightly is maybe the ambiguity of "beam span" over "beam length". Span is from attachment point to attachment point (ledger to support post ), where as length is from one end of a board to the other.

Do not, by any means, take this as a definitive answer, more research would be recommended. The best place to start would be your local building department, because it doesn't matter what the rest of the world does, it only matters what is allowed in your own jurisdiction. 8-)
Yes that is correct for beams I would say, joist cantilevers I am sure are different though.
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Shannon
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Re: New deck posts

Post by Shannon » Thu Aug 10, 2017 11:05 pm

I had a look around as well and that does seem to be a general rule of thumb even for joists. But actual onsite loads and conditions would also dictate I would think because not all situations are the same. But in general it looks like in most cases for an average deck this could be true. The cantilever would be based on the proper sized joist for the proper span also. In my mind a max. of 36" would be a good place to stop though.
Had a good look at that chart in the second source you had. It would seem to me that that chart has a few numbers in the wrong columns? In many of them as the joist spacing gets wider the cantilever amount gets further??? That does not seem right?
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Re: New deck posts

Post by A. Spruce » Thu Aug 10, 2017 11:35 pm

Another site said that cantilever shouldn't exceed 3X the joist height. The problem with the "sources" above is that they simple came from sites, they were not quoting code and I didn't see an actual code reference, but again, that was a VERY quick look.

Ultimately, I'll stand by what I closed with, and that is to check with your local building department for their standards and regulation on decks and cantilevers, especially if this project is being done with permits and inspections.
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Re: New deck posts

Post by Shannon » Fri Aug 11, 2017 7:15 am

Yes absolutely you must go with what your local building dept. dictates.
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