deck movement?


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Old 06-27-08, 10:19 AM
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deck movement?

We have almost completed our deck - we just have to finish getting the railing up then have the last inspection.

We built this deck over our 3 foot retaining wall. At its highest the deck is about 5' off of the ground - and as it comes up and attaches to the house it is about 2' off of the ground there.

We used composite decking with 4"X4" inch posts attached to case-ons (sorry, not sure of all of the technical words like my husband ) - these were all approved by the city.

My one and only concern is that it seems like when my dogs (total 175 lbs of labradors) run off of the deck I can feel it shake a bit. Is this normal? It's not like I can "see" it shake, but definitely something I can feel.

Before our final inspection I want to make sure we can do everything possible to pass.

Our deck goes off of our house approx 12ft and is approx 20 ft wide. Our joists are 16" apart (per code)

Thanks for any and all info
 
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Old 06-27-08, 11:14 AM
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Probably the spacing of the joists. "Most" composite decking has more flex to it than "most" wood deck boards. Not sure if its a problem to be addressed or more of an annoyance if it bothers you.

Wait for one of the Pro's, but I saw a post a while back, that one of them now spaces his joists at 12" because of customer concerns about the feel of bounciness.
 
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Old 06-27-08, 01:24 PM
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Thanks
Yeah, it's not really a "bounce" more of a "shake" if that makes sense. It's not a huge annoyance...I just want to make sure it's okay if it does that..and if not..what we need to reinforce to make it stop
 
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Old 06-27-08, 03:02 PM
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Like i said, I'm sure one of the Pro's will weigh in eventually.

Anyway, I probably would have gone with 4x6 or 6x6 posts myself, not sure if thats a requirement, but I prefer to overbuild. I have noticed that 4x4's are not the same everywhere. I was used to Southern Yellow Pine treated lumber back in VA, now here in AZ it seems like its balsa...
a 4x4x8 here weighs less than a good 2x4x8 from back there.

On the 5' end, do you have diagonal supports from the rim joist(?) to the posts? (Sorry, been out in the 105 heat working on my own sorta deck project)

If its not bouncy, then your joists should be ok, esp if reviewed by the Inspector.

Is it nailed, screwed or bolted? The real experts are probably going to ask.

Don't know what else to ask. Reinforcement and bracing never really hurts. It will probably only annoy you more and more as time goes on.
 
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Old 06-27-08, 04:38 PM
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Movement

Is the movement vertical or horizontal?

Vertical movement could be reduced by adding blocking between the floor joists.

Horizontal movement could be reduced by adding diagonal bracing attached to the posts and the rim joists.
 
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Old 06-27-08, 05:03 PM
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It seems to move side-to-side/type shaking if that makes sense.

We dont have the diagonal posts in between the posts. Maybe that's what we're missing.

Is there somewhere I can see how this is done?

Thanks!

Oh - it's also done with all screws - no nails at all. I know there are what look like either huge screws or bolts that go on the attachments that attach the beam and posts.
 
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Old 06-27-08, 05:12 PM
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Thats good, lag bolts or bolt and nut. Sounds like you need the diagonal bracing, which makes sense with a 20ft deck.

Its pretty simple, 2x6 or 2x8, bout 2 ft long or so, 45 dgree angles on each end, lag bolted to the rim joist and the post.

Hubby does know yer on here looking for advice, doesn't he...lol
 
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Old 06-27-08, 05:25 PM
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The books on lumber engineering give allowable deflections and recommended floor loading, and how to achieve them.
I've worked in commercial buildings that had the floor shake when someone walks by 10' away.
Sometimes an e-mail to your county permit guy may clear this up.
 
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Old 06-28-08, 10:51 AM
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Originally Posted by Gunguy45 View Post
Thats good, lag bolts or bolt and nut. Sounds like you need the diagonal bracing, which makes sense with a 20ft deck.

Its pretty simple, 2x6 or 2x8, bout 2 ft long or so, 45 dgree angles on each end, lag bolted to the rim joist and the post.

Hubby does know yer on here looking for advice, doesn't he...lol

ha! Well he knows I want to make sure a little bit of "shake" is okay. I guess we have already paid all of our permit fees so I could just have the city department out twice if need be - does he know that I am researching it as much as I am? Maybe not But he will if we need to do the diagonal bracing...which is what it sounds like

I guess I am not "seeing" the diagonal bracing right though...I am sure my deck book probably shows something like this I just dont remember seeing it.

Or I suppose I could just stop trying to micro-manage his project and let him find out for himself That sounds like a good idea


Thanks!
 
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Old 06-28-08, 11:35 AM
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Think of your post attachment now...when you look at it, it looks like a "T" with the post being the downward leg and the rim joist being the top horizontal of the "T".

The diagonal bracing would make the "T" look like a "Y" has been layed over top of the "T". Its just adding those 2 diagonal parts of the "Y" to the "T". You put them on the back of the rim joist and the post and bolt or lag bolt them through.

Sorta like you might see in front of the saloon or the ranch house in an old western, though lots of those were timber framed, but similar thinking.

Amazing how much difference it can make in the movement or a deck.
 
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Old 06-28-08, 05:13 PM
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Oh I can see it now - I was figuring we needed post attached to the bottom of one post (by the case-on) up to the top of another. But it probably only goes down the post about 2 ft?

Would you need to cut the post (brace) diagonally to attach it to the joist - or do you just attach it to the beam.

Also, is it normal for the wood of the frame to crack a little bit? i have noticed our beam is treated wood however it has a crack that kind of moves down the middle - not all connected..it just looks like its from all of the screws in there and stuff.

Thanks again.
 
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Old 06-28-08, 05:23 PM
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2ft down would be plenty on your 5 ft posts. You could probably go a bit less, 18" or so. Each end of the brace would be cut at a 45 degree angle so it fits.

Yes, treated wood splits like you describe. Would be nice if it didn't, but thats a fact of life.
 
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Old 06-29-08, 03:05 PM
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Also, just saw a fix in a mag I get. You can attach a 2x4/2x6 under the deck going from corner to corner in both directions. If theres room close to the house. Just screw or nail to every joist. Less visible and probably just as effective. Helps reinforce the floor joists too.
 
 

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