Span


  #1  
Old 05-12-03, 12:19 PM
slavetohouse
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Wink Span

I am planning to build a 22 x 16 deck. The concrete footings are already in and are 16' from the house (about 7 feet apart). I plan to use 2 x 12s, 12" o.c. to span the 16 feet from the ledger to the beam. The "beam" will essentially be the front edge of the decks framing (2-2x12s sandwiched together) using joist hangers to support the joists on both ends (ledger and beam). The beam will span 22 feet total, but really only 7 feet between the 4 posts that go down to the footings. I plan to use Trex decking.

Is this feasible? I am concerned about the span and also the fact that there will not be a separate beam that runs under all of the joists.

Thanks for any help.
 
  #2  
Old 05-12-03, 03:58 PM
L
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That's not the way I would do it.

I would add 2 mid-span beams between the house and footings that are already in, and set a third beam on that footing. Now there will be 3 beams about 5 ft. apart. Since you are supporting the beams with posts set about 7' apart, use double 2X8's or 2X10's for your beams. Then, use 2X6 joists and the ledger, with the joists attached to the ledger with the hangers, and resting on all 3 beams. If you are using 2X6 Trex, joist spacing is 20" max. If you are using 5/4, reduce that to 16" max.

I would actually add a 4th beam, about a foot out from the house, eliminate the ledger, and make the deck free standing. But that's just me. I prefer not to attach my deck to the house unless there is a very compelling reason to do so.
 
  #3  
Old 05-12-03, 04:30 PM
slavetohouse
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I am afraid I cannot add all the extra footings that would require due to the rocky terrain. I just had this house built and the builder already put on the ledger board and poured the footings since he needed heavy equipment to dig there. So I am stuck with the four footings out 16' from the house. I asked for them closer but there were problems digging that resulted in them being 16 feet out.

Simply put, can 2x12s span the 16 feet I need at 16 o.c. spacing or do I need to go 12 o.c.? Also, Will my "beam" (doubled up rim joists, I think they are called?) be able to span the 7 feet between the posts out at the end of the deck?

Thanks very much for your insight.
 
  #4  
Old 05-12-03, 09:20 PM
L
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Why all the footings if the deck is going to be attached to the house? A hole 5" or 6" deep, 18" in diameter, fill it with ready mix and set a pier block in it. The outer beam already has it's footings. Everything else is just there for support, NOT to keep the deck from moving!
 
  #5  
Old 05-13-03, 05:15 AM
slavetohouse
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I guess I am not explaining myself well. The footings are 4 foot deep cement things that will support the end of the deck oposite the house. I kinda need them.

For the 3rd time, I am going to ask the question: Can I span this distance with the lumber I plan to use.

FWIW, there is more than 1 way to skin a cat or build a deck.
 
  #6  
Old 05-13-03, 07:03 AM
petrsjo
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The answer to your question is: probably, depending upon your local code.

If your code requires only 40psf live load and 15 psf dead load, treated #2 Southern Pine can span about 19 feet at 12" spacing, or 17 feet at 16" spacing. I would go 12" o.c. as the 17 foot limitation cuts it kind of close.

You can check out span tables at www.wwpa.org or www.cwc.ca.

Based upon the same assumptions, the rim joist (beam) of doubled up 2x12's will be more than adequate. However, I would suggest NOT using joist hangers on that side of the deck. Rather, if you can lower the rim joist (beam) and run the joists over the beam. You can even cantilever the joists another foot or two past the beam, giving you another foot or two of deck depth.

How big (diameter) are your footings?

John P.
 
  #7  
Old 05-13-03, 07:12 AM
slavetohouse
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Thanks for the quick reply.

I appreciate the insight on the load requirements.

The footings are the bell shaped kind so the bottom (burried part) is quite large (maybe 20"). At the top it is about 10".

It sounds like I should be okay. The decks I have built in that past were not as far off the house and I did use the support beam under model.

If I move the beam under, perhaps I could use a tripled up 2x8 rather than a doubled 2x12? What do you think?

In that scenario would you say I could use a single RIM joist at the end?

Again, thanks for hanging in there with me.
 
  #8  
Old 05-13-03, 07:36 AM
petrsjo
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The footings are a good size - definitely no problem there.

For the beam, I would go to a tripled up 2x10 approach. Tripled 2 x8's might be okay, but since that is your main support artery, I tend to be conservative. Again, it depends on your minimum code requirements. That's also why I would put the joists 12" o.c.

If you cantilever the joists, you only need a single rim joist, since it's not a major support piece. I also prefer the cantilever because 1) it hides the footings and posts a bit, 2) it gives you more deck space, and 3) it's a better structural approach than the joist hangers (in my opinion).

If you really want to go nuts (and have 15 bucks to spend) try www.bestdecksite.com. It has a tremendous amount of information regarding the structure of a deck.

John P.
 
  #9  
Old 05-13-03, 07:38 AM
slavetohouse
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Excellent. Thanks for all your help. Have a great day!
 
 

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