Uneven Joist

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Old 08-19-19, 10:29 AM
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Uneven Joist

I'm putting a composite deck up. I'm noticing as the surface is installed that one joist is a bit higher than the others and giving a bit of a waving effect. The joists were installed with the bow pointed upward. There is some space between the girder and joist which I had shimmed, but removed with hopes that it'll sag to the height of the others with the height of the decking and people standing on it. With a 2x10 joist, will it sag if I leave that space? How long will it take? We're talking about 3/8 - 1/4" higher maybe -- not an inch.
 
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Old 08-19-19, 11:58 AM
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Besides being crowned or bowed, joists sometimes vary in width. Its often good to check the surface of the joists with a straightedge before any decking is even applied, planing down any high spots with a power planer before you begin laying out your decking.

Don't plan on one joist sagging to match the others.
 
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Old 08-19-19, 12:57 PM
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With 1/3 of the boards already on, power planing isn't a simple option right now. Will a 2x10 on end usually sag to meet the joist over time?

It is something you can't notice while standing on the deck, but can when closer to eye level so I'm not looking to tear down what I did, but if I can make small structural changes that could help, I'm open to it.

Thanks for the reply!
 
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Old 08-19-19, 01:19 PM
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They will all move over time. So I wouldn't obsess over it too much. Even if they were all perfect, they will likely move up and down in a year or two. You can't really control or predict how wood warps. 2x decking helps hold things straight better than composite does.
 
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Old 08-30-19, 10:26 PM
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Planing deck frame

Your best start is to plane the effected 2x before installing the deck boards. Pressure treated lumber is usually still wet when installed. There is a very likely chance that as the 2x dries out, the warp will be even greater. You may be able to attach a 2x under the joists, the length of the deck and pull the joist down using framing hangers, lags or screws.
 
 

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