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Old 08-14-2012, 01:59 PM   #1
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To all you deck experts, I'm looking to redo my existing deck. The old 12'x20' deck is 25 years old and too small for our house parties. The old deck is a second story deck (approx 9' above grade) on 6x6 posts with 2x6 decking. I plan to completely remove the old deck except for the ledger. My plan for the new deck is to increase the size to 18'x40' (the 18' is from the house) and put a roof on it and use 8x8 posts. The new deck will be all one level but, dog-eared on the corners. I plan to put the girder at the 15'-16' mark (3'-2' cantelever). The girder will be 2-2x10s and will rest on top of the notched 8x8 posts. If I use 5 posts, I calc the worstcase sqft per post at 105. If my design loading is 65psf (40LL + 25DL), that calcs to 6825 lbs per post (worstcase). How does that sound so far? Is that too heavy for a 8x8 post? Also, what size footer do I use......can I get away with 24" sonos w/ a simpson 1" plate? My frost level is 10" below grade (I'm in NC).

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Old 08-14-2012, 03:10 PM   #2
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That beam is overspanned quite a bit, that would put posts at 10' correct? 0',10',20',30',40'? your joists are going to have a fair amount of deflection as well with those spans. Pier sizes will be dictated by loads applied by the deck and the roof, as well as soil conditions, 24" seems a little undersized for both. I've a number of times had 30" diameter piers where a deck and roof shared a pier. The 8x8 posts should be sufficient.
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Old 08-14-2012, 03:29 PM   #3
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That beam is overspanned quite a bit, that would put posts at 10' correct? 0',10',20',30',40'? your joists are going to have a fair amount of deflection as well with those spans. Pier sizes will be dictated by loads applied by the deck and the roof, as well as soil conditions, 24" seems a little undersized for both. I've a number of times had 30" diameter piers where a deck and roof shared a pier. The 8x8 posts should be sufficient.
I think you're right. If I add another post, that would make it 8'. And, use 3-2x12s instead. How does that sound? I calc the joist span to be about 15'......is that too much? I'd rather not put in a girder midspan.

Also, the NC soil is the worst. I think I saw that it has a bearing cap of 1500 psf.
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Old 08-14-2012, 03:46 PM   #4
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That would be better for the beam, I would bring your end posts in a little bit and let the beam cantilever over the posts 12"-18" and then evenly space the rest of the posts, this will give a little more strength by shortening the span between the posts. For the joists I would recommend MINIMUM 2x12's @ 12" O.C. 8" O.C. would not be a bad idea. The piers may need to be even larger due to only 1500lb capacity.

This sounds like a heck of a project to undertake, are you going to DIY it? what kind of roof are you going to do? shed roof off house? gable end? Trusses? or stick built?
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Old 08-14-2012, 05:17 PM   #5
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bugman,

check out this link, it will provide you the spans for beams and joists for your deck. it does not address the roof you are planning on building. http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf

This is the Prescriptive Residential Wood Deck Guide based upon the 2009 International Residential Code. Should provide a lot of the information you're looking for.

Good luck!
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Old 08-14-2012, 06:18 PM   #6
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That would be better for the beam, I would bring your end posts in a little bit and let the beam cantilever over the posts 12"-18" and then evenly space the rest of the posts, this will give a little more strength by shortening the span between the posts. For the joists I would recommend MINIMUM 2x12's @ 12" O.C. 8" O.C. would not be a bad idea. The piers may need to be even larger due to only 1500lb capacity.

This sounds like a heck of a project to undertake, are you going to DIY it? what kind of roof are you going to do? shed roof off house? gable end? Trusses? or stick built?
2x12 joists it is! I did not realize at first that the second section of the Maximum Joist Span table shows the joist spacing w/ the overhang (cantelever). I was thinking the span was just from the ledger to the girder. However, I don't think my local lumberyard has 20' 2x12s SYP ACQ. So, would 2x10 @ 8" O.C. suffice?

I am using a shed style roof using 2X10s rafters. I plan to have a metal roof because the pitch will be a 2:12 to 1:12. I also plan to have 4 skylights and use T&G decking. What would be the best way to support the roof? Because of the low pitched roof, I think I have to move the roof posts out to the deck rim. I was thinking of using 8x8 posts that rested on floor joist blocking. I would like the roof to overhang the deck about 24" so I can hang a typical gutter system.

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Old 08-14-2012, 06:25 PM   #7
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I know its NC, but you still get snow down there on occasion. The typical deck code does not address loading from roof structures, which adds to the live load on the deck, but typically as point loads, since the snow weight plus roof is normally carried down to the deck via posts. I would discuss your situation with the building inspector first, since all of your design seems to be based on standard deck code, which as I pointed out does NOT apply when you have a roof. If you carry all roof load down to footers via posts, your inspector may allow you to size the deck per code, but that is their call. Unless of course you live in a county with no code and no inspector.
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Old 08-14-2012, 06:41 PM   #8
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I know its NC, but you still get snow down there on occasion. The typical deck code does not address loading from roof structures, which adds to the live load on the deck, but typically as point loads, since the snow weight plus roof is normally carried down to the deck via posts. I would discuss your situation with the building inspector first, since all of your design seems to be based on standard deck code, which as I pointed out does NOT apply when you have a roof. If you carry all roof load down to footers via posts, your inspector may allow you to size the deck per code, but that is their call. Unless of course you live in a county with no code and no inspector.
It is true that NC gets snow but, it definitely matters where the deck is located in the state. I live in the South most part of the state away from the mountains and the extreme snow load. I think my 25DL psf will cover any snow in my area. With 6 posts, I re-calc that to be 5460 lbs per post. And, 5460 lbs/1500 psf equals 3.64 sf. So, a 24" sono would barely not cover it. I could either use a portable compactor, use a 30" sono, or use spread footers.
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Old 08-14-2012, 11:28 PM   #9
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Your roof posts will need to stack and transfer load down to the footings unless you want to do some crazy heavy duty structure. Did you include the roof loads in your calcs? you'll be looking at some hefty piers for sure. Call in the concrete truck when it's time to fill them up.
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Old 08-15-2012, 08:28 AM   #10
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Your roof posts will need to stack and transfer load down to the footings unless you want to do some crazy heavy duty structure. Did you include the roof loads in your calcs? you'll be looking at some hefty piers for sure. Call in the concrete truck when it's time to fill them up.
The roof posts and everything it supports (the rafters, roof girder, skylights, T&G decking, roof material, gutters, nails, etc) has to transfer down to the footings. However, my roof posts are not the same piece of lumber as my deck posts. I moved the roof posts out to the rim of the deck. I said in my previous posts that I raised my DL up to 25 from the typical 10 or 15 to account for the roof system. In my calc, I have accounted for all loads.

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Old 08-15-2012, 04:02 PM   #11
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If I'm understanding what you're saying correctly you want to build something like this picture but with a roof instead of the upper deck... Let's just say you'll need an engineer to design that kind of structure, this one was NOT engineered and it was VERY dangerous.
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Old 08-15-2012, 04:13 PM   #12
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In my calc, I have accounted for all loads.
did you account for all lateral loads?
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Old 08-15-2012, 04:14 PM   #13
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Robert,

that is one scary deck!!!! thanks for the post!
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Old 08-15-2012, 04:23 PM   #14
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Robert,

that is one scary deck!!!! thanks for the post!
We built a wall under the upper deck just over the beam just so we could tear the upper deck down safely. I am fully convinced that the double 4x4 post on the corner was the only thing keeping it from failing catastrophically. We replaced it with this. A much safer design and he won't have to worry about his deck again in his lifetime (or mine).

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Old 08-15-2012, 05:34 PM   #15
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It appears in the scary picture that the cantilevered portion of the deck is about 48" and supports another deck that had the potential of carrying 40ll + 10dl. I agree this did not look safe but, the load I plan to support with the cantilevered portion of my deck is pure dead load (~10dl). Also, the scary picture has 4x4 post.......yikes. I think putting a load bearing wall on a cantilever is done all the time for residential houses but, the load it is bearing is never a second story, its almost always the roof.

I appreciate the discussion. Obviously, I need to make sure this is done right.

What decking material is the bottom picture? Also, do you happen to know the dimensions of the main part of this deck? It looks great!

Last edited by Bugman1400; 08-15-2012 at 05:36 PM.
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