Deck Sturdiness


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Old 08-25-06, 08:58 AM
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Deck Sturdiness

I'm in the process of building a deck off the back of my house. Its attached to the house then an 8ft span 3 posts and a 12ft span for the final set of 3 posts. I notched the posts and used two 2x10's for the joists to sit on top of. I thought this would be a nice transfer of the weight but now it seems that the deck is "floating". If I walk to the end and move back and forth I can feel and see the deck swaying. I'm thinking about two possible solutions. 1. cut 45 degree Y for the post to better hold the ledgers in place. (and or) 2. Making an X from post to post with 2x4's. Any suggestions/help would be much appreciated.
 
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Old 08-25-06, 10:35 AM
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Deck

Tell us more:

1. How high is the deck above the ground?
2. How deep in the ground are the posts? Or are the posts on top of concrete pillars?
3. What size lumber did you use for the posts?
 
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Old 08-25-06, 11:06 AM
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Sorry for the little info,

The deck is about 8.5 ft off the ground. I went with the 6x6 posts and I didn't cement them into the ground wich I'm regretting. I used steel feet on them and bolted the feet into about a 3ft deep auged hole filled with cement.

The deck is about 16 ft wide and 21 ft long. I'm doing the stairs now and I made a landing with cemented in posts that I'm going to tie into the last set of posts to also maybe help the sway.

Any ideas as to what would stop the structure from moving left to right? Do you think I'm heading in the right direction with the Y and X's on the last set of posts into the ledger?

Its very stong near the house its just the further out you go the more wiggle it has. For the ledger attatched to the house I went through brick and into the floor joists of the house so I think that was done right. Thanks in advance for any advice.
 

Last edited by TooTall; 08-25-06 at 01:28 PM.
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Old 08-25-06, 02:06 PM
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Deck Sturdiness

You need diagonal bracing.

It can be parallel to the home at the outside. You can run diagonals from the base of one post to the top of the next post. Doing this is in 2 bays is better than doing it in one. The only problem is that does not look good.

You can also add diagonal bracing to the underside of the deck. This can be long 2x4s well nailed to the bottom of each joist. Probably not as effective, but more attractive. You could try it come back toward the house from each of the outer corners.

Anytime you nail wood, you do not get rigidity at a joint. The hardware will help, but nothing beats basic, sound structural principles.

Dick
 
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Old 08-25-06, 03:12 PM
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You haven't said so, but it sounds like your 1st mistake was not pulling a permit to build the deck. A 12' span with dbl. 2X10's is probably a bit too much. Your post or column bases should have been EMBEDDED in the footing, not bolted to it. (That requires a different base than what you used.)

Diagonal bracing (betweent the posts parallel to the house and from the posts to the beams perpendicular to the wall of the house) or diaphram bracing (bolted to the bottom of the joists diagonally from the wall of the house will help.
 
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Old 08-25-06, 09:37 PM
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It sounds as you are on the right track. A little overkill for structural support never collapsed a project if you ask me. I don't see whether a premit or not has anything to do with anything. Actually, my local codes call for a double 2x10 support beam for spans less than 10'. Over 10 requires a double 2x12 and the max of 16' requires a triple 2x12. Over 16' requires 2 sets of beams. Those spans don't count the 2' canteliver allowance, by the way, that's actual wall to beam spans.

Anyway, on the subject, my question would be, "have you laid the deck material yet?" because that helps sturdy up a higher elevation deck. Croos braces are definately in order, but how you go about them is subject to interpretation. My style has always been to cut them into the 6x6 post anywhere from 2 to 4 feet below the beam 45ed up to the beam (depending on the height). I've found that lag bolting these in adds to greater support in the long run.

Here's a link to a picture of a deck I built many a year ago;

http://img175.imageshack.us/img175/945/decks21br6.jpg

If you copy and paste that into your browser you will see what I'm talking about as far as the cut in to the 6x6. It's an old picture and the beam system is a little ridiculous under that deck, but it's the only one I could find that showed that cut-in. And no making fun of the work, I've improved over the years.
 
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Old 08-26-06, 06:19 AM
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Troy141,

The permit has EVERYTHING to do with the issues that TooTall is going through. (Of course, the permit process varies GREATLY from one place to the next, and we don't know where TooTall is or what his local bldg. dept. requires, so some of this may or may not apply in his case.)

Every jurisdiction that I deal with (build in) has essentially the same process. You submit a set of plans with your permit application. Those plans are then checked to insure that what a person will be constructing is sound and meets codes. Once the plans are approved, whoever is building can start and will have some inspections thoughout the construction process. In the case of a deck, the first inspection is the footings. The holes are looked at to make sure that they are the right size and style before the concrete is poured. Any post bases, column bases or pier blocks have to be on site at the time of that inspection. The ledger needs to be in place too so it can be inspected while it's still visible. TooTall's bases, at least where I build decks, wouldn't have passed.

The next inspection is framing, and is usually combined with the final when all of the framing is visible, as in the case of a deck that's 8' above ground. The inspector would have caught the lack of bracing under TooTall's deck and required that be in place before he (or she) would sign off the deck.
Those are the reasons that a permit would have made a difference.

TooTall, I'm not picking on you or your deck. I don't know where you're at or what your local bldg. dept. requires (and that varies GREATLY from one place to the next!!) But a deck that sways is not a safe deck, and that's what 90% (or more) of the building codes and inspections are all about -- SAFETY!
 
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Old 08-26-06, 10:36 AM
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Good points Lefty, I'm in agreement, and that's pretty much the same process where I am from (Chicago area). Most town municipalities provide a small guidebook when you apply for a permit which explains the local codes, so ya, a permit would have been a good idea. For me, I've just always found them to be a timely & costly pain in the butt once you know what the codes are, but I should leave the personal opinion out of the topic, so, I apologize.
 
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Old 08-29-06, 09:30 PM
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Troy141,

As a DIY'er, you know what the codes are -- or at least what they were the last time you dealt with such a project.

For me, a contractor, it doesn't work that way. When the codes change -- and they do every year or so -- I have to build according to the NEW code!

For you, the DIY'er, you build according to what the codes WERE, and you'll be changing it when the inspector turns you down.

THAT'S another reason why a permit is so important. You build it to the APPROVED PLANS and you won't have that problem. It sure saves a lot of work and aggevation!!
 
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Old 08-30-06, 06:32 AM
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TooTall,

Troy141 asked the question "have you laid the decking material yet?". If the answer is no, then you should consider laying it on the diagonal. That will provide considerable resistance to the swaying you are experiencing. If you have already laid the decking, I would suggest what Concretemasonry suggested, puting diagonal bracing under the floor joists. If you decide to pur braces on either side of the posts, they will not have to reach all the way top to bottom, as your 6x6 posts are more rigid than 4x4 - angled braces from the beam down 2 1/2 feet on the posts should be sufficient. Notched 6x6's (like the top of your posts) extending up into the beam, and lag screwed to the posts should give the support you want, and look like part of the original plan versus a bold-on fix.

Your stairs may help to stabilize the deck, but I wouldn't count on them for all your bracing - brace first, then tie in your stairs.
 
 

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