Deck extension support

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Old 11-16-16, 11:09 AM
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Deck extension support

I want to add a 6'x2' deck extension but unsure how to support one corner. A ledger against the house will support a 2' side and I will bolt a 6' side to the existing deck. The existing deck is about 15' high supported by 2 steel beams so it is complicated to add a support to the ground for the extension. I am thinking about building a bracket with 4x4 or 4x6 and attaching to the house (hardiplank) to support the corner. It will attach to the house about 6 inches from the corner (there is a gutter downspout at the corner). I haven't attached anything to the outside of a house before so a little unsure if there is anything special to consider.
 
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Old 11-16-16, 11:11 AM
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A picture or drawing would really help.
 
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Old 11-16-16, 11:42 AM
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Clearly a picture would help as suggested earlier.

I'm concerned about your approach. So, in effect you're building a 2X6 platform held up on one 2' and one 6' side and asking about supporting the far corner - which is probably fairly easy. Even if you can easily add that support, I'm concerned about the 6' span given that you'll be 15' above ground. Obviously it depends on the size wood you're using but I'd consider adding 2 joists at 2' and 4'.

Rather than "building a bracket" there's probably products available we can suggest after seeing the picture.

Hardiplank can be removed and replaced with care.
 
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Old 11-17-16, 11:56 AM
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The first picture is a quick drawing I did showing the extension (ignore the posts)
Then a shot from below (sorry it is sideways)
And finally one from the deck

i am flexible on the exact length of the extension - planning 2 feet so deck boards are exactly 20'. But could add 6 more inches to get it closer to the corner of the house (where I know there are several 2x6 behind the wall to attach a bracket. My questions are regarding supporting the corner that is not attached to the house or deck. I plan to build the extension out of 2x10 which is what the main deck frame uses.

The bracket I was thinking about would be 5' against the house and 5 or 6' under the deck frame using 4x4's and then brace it with a 4x6. This brace/bracket is what I am not sure about - especially attaching it to the house.
 
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Old 11-17-16, 12:06 PM
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Here is my inspiration for the "bracket"
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Old 11-17-16, 12:44 PM
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Would be nice to see the entire front of the deck from afar, and something that shows your current post connections to the deck. Would also be good to know the joist span, size of dimensional lumber used and the distance between your existing posts.
 
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Old 11-18-16, 08:58 AM
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Attached are two views of the deck. I am planning to replace the decking and rails.
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Old 11-18-16, 09:48 AM
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Frame is 2x10, joists are 2x8 at 16". Support beam is about 2' from outside edge. Looking at picture, support beams are 2' from edge, then 7' then 7.5'.
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Old 11-18-16, 11:03 AM
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Thank you for the photos. A few more questions, what is the total length of the joists, and how far is it from the house to the beam? Are the joists sitting in joist hangers at the ledger? And are there any hurricane ties connecting the beam to each joist? Finally, what is at the base of your posts? Does a cement slab extend around them?
 
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Old 11-18-16, 02:52 PM
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Deck is 12 x 18 so joists are almost 12'. The steel beams are 10' from the house. The joists are nailed into the ledger - no hangers - but they also sit on a 2x2 that is nailed to bottom of ledger. No hurricane ties. The top of the steel beam is an L shape with the beam nailed into the support beam. Name:  image.jpg
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Old 11-18-16, 03:01 PM
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Ok, did I miss where you told me what size your beam is? The beam sits on top of your steel columns. I'm guessing it's a 2x10?
 
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Old 11-18-16, 03:59 PM
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Ok, i'm going to assume the beam is 2x10 and try to answer your question.

If we use the DCA 6, (2012 IRC), and assume all your lumber is pressure treated SYP, everything you currently have checks out, except you will want to add joist hangers in place of the 2x2 cleat. And add some Simpson H1 or H2.5 connectors to each joist on your beam. You will also want to add two lateral load devices on each end of the ledger, as shown in Figure 22 in the link above.

There are bound to be differing opinions of how you should tackle this small deck addition. I will say up front that your corbel brace idea is not going to work. Here is what I would probably do if you want to extend the deck 2 ft on the left side of your pictures.

Once you remove the decking and railing, temporarily support the outer rim of the deck with three 6x6s that you notch and lag bolt to your rim. Cross brace these temporarily so the posts stay plumb and the deck cannot sway laterally... left or right. Then remove your steel columns and double 2x10 beam.

You will want to replace that beam with a new one that spans the entire 20 ft. (You could probably splice it, if your splices are staggered, and directly over your columns, that's up to you.) Reinstall the beam, toenail it to the joists and connect it to the joists with either H1 or H2.5's.

Now here is the problem. A 20 ' 2x10 beam needs 4 columns instead of 3. Allowable span (DCA 6 table 3A) between columns is 7' 9"... allowable cantilever is just under 24". So you are like 6" over specs if you go strictly by the code book above. If you don't have any codes to worry about where you live, it might be different... it's very close.

The easy thing things do is to have 1 more column made and space them 6 ft apart... at 1, 7, 13, 19'... placing them on new footings.

If you aren't wild about having another column made, the only other option would be to replace your double 2x10 beam with one that is double 2x12. It would mean shortening your steel columns, but any welder could do that for you. Then you would only need to move 2 out of 3 columns... the one on the right could stay put (maximum of 27.5" beam cantilever from edge of deck to column) the one on the far left would move out farther left to match the one on the right, and the one in the center would get centered between them. If you change your beam to a 2x12, the maximum distance between columns is 9' 2", so in that case they could be at 1', 10', 19'.

Once you do all that, you can add 2 ft to the deck. If this sounds like too much work for an extra 2 ft, I would agree and suggest you forget the idea.

The only alternative idea that would involve less work is to leave all the columns as is and add a 4th one 2 -3' to the left of the far left one. Then splice your beam to extend it out 2 ft more than it currently does. Then you could add the 2 ft of new joists.

Your deck is also missing diagonal bracing (figure 10). Maybe if those steel posts are set in concrete, an exception was made. I would think it would sway laterally in front. That one cross brace underneath doesn't seem sufficient.
 
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Old 11-19-16, 08:33 AM
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Thanks for the advice on the existing porch. It will be helpful to follow when I replace the decking and rails. I am unsure of the beam dimensions but believe your assumption is right. I also mixed my terms (post versus beam) but it sounds like you understood.

Obviously you are trying to talk me out of the extension which I think you have. I did consider extending the entire deck following similar options as you suggest but realized it was too much effort which is why I considered a small extension. The extension is to move the grill out of the main deck area. So not a big deal to not add the extension.

You say the corbel brace is not going to work - i would like a little more insight so I can increase my knowledge. Is the issue because of the distance / size of the extension or because the brace itself is not an appropriate support for a deck? I have seen a brace used for small balconies so assume the issue is the length away from the house. It seems like this is an effective approach for supporting a porch a couple of feet from the house.

Would the brace be more appropriate if I shortened the extension to 4' or 5' instead of 6?

Thanks again for the advice / insight.
 
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Old 11-19-16, 11:27 AM
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Ok, well what i was describing was a 2' x 12' addition. Not a 2' x 6' addition. Maybe that changes things.

Either way, a corbel brace probably won't work for multiple reasons.

I think you must be picturing one corbel, mounted perpendicular to the house, apparently supporting joists that run in the opposite direction of your existing joists. I don't think that would work. You would need structure in the wall to support the corbel attachment, which is likely not there. The corbel would also need to be very large to support your extension. I'm not qualified to design it or say how big it would need to be... so keep reading.

If you want the joists to run the same direction as the others, you would need a pair of corbels, and they would need to be mounted parallel to the house on 6x6 columns. But if you are willing to put columns in, you would forego the corbels in favor of a single column... placed on the outside corner of your proposed "addition". So why aren't you willing to just put in one new column (2 feet left of the deck edge and 6 feet away from the house) so that you can build your "addition"? That would make it more closely resemble the very first picture in your post #1.

Secondly, structural corbels are not really part of the building code in most parts of the country, and as such I don't know too many building inspectors who would allow it. Corbels are not the norm when it comes to decks, so I doubt they would approve the plans. If they did, it would have to be based on a drawing of a structural engineer who would assume the liability for the structure as drawn, similar to how structural roof trusses are designed and used. Someone designs it, tests it to a known quantity/capacity, then it must be installed in an approved, designed manner so that it will perform as it was meant to. This is true whether the structure is made of wood or iron.
 
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Old 11-19-16, 01:43 PM
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This has been really helpful and I really appreciate the expertise. You are right, a new support pole would be best. But makes sense about the corbel bracket being something out of the norm. I will just leave the grill where it is and replace the decking and rails.

Thanks again.
 
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