# Composite decking on joists that are not perfectly level



## Ron6519 (Mar 28, 2007)

I'd adjust the joists so the deck boards are in the same plane.
The result will be:
1. it will fall into manufacturers specs.
and
2. it won't look wavy.
Two birds with one plane.


----------



## ront02769 (Nov 28, 2008)

If you have framed with presure treated jpists, and get them perfect
Y level, they will be again out of level in six months or so. Ron


----------



## gregzoll (Dec 25, 2006)

It all depends on if someone went every other one with the crown being opposite of another. It should be Crown Up, so that over time, it will lay flat as the boards start drying out.


----------



## ChuckF. (Aug 25, 2013)

Re: "Adjacent joists appear to be 1/8"-3/16" off."

Are you saying they are warped so they are off in the center of their span, or are they off that much all along the full length of the joist?

If the former, are the joists long enough that you can pry-bar them into level and then install blocking to keep them that way?

If the latter, how did that happen?


----------



## cjdavia (May 28, 2010)

Thanks for your responses. 

Long story short -- last year a contractor started framing the deck but never finished. This year a new contractor took over and continued where the other left off.

Some joists are not level by about 1/8"-3/16" between adjacent joists. The joists are 16" apart. In other words, one side of the joist bay might be 3/16" higher or lower than the other side so when I lay the decking down there can be a 3/16" difference across the 16" inches. And then maybe another 1/8" difference to the next joist over the next 16 inches. The joists themselves appear to be pretty much level across the full 18' length of the joists.

The latest carpenter already did some planing and shimming so I can't really tell where the crown is anymore. In order to bump up the two joists that are low, I guess I can remove some hurricane brackets and joist hangers, shim, and re-install as you suggest but I am concerned that when I reinstall them they will not be effective since I'm moving the joists up by such a small amount.

What do you think about shimming the tops of those joists? I can rip a strip of PT, nail it on and then wrap the whole thing with watertight deck/joist tape. For the low spots, what do you think about using an extra pice of joist tape to make up the difference? 

I just purchased a hand planer to help with the high spots but I can see this is going to be a long and frustrating process.

I know you are all trying to help but I think a great place to start would be "How level is level enough"? 

For those of you that have success installing composite capstock do you stop planing and shimming when you are dead level, or within a threshold of like 1/8"?

Thanks so much


Any help or suggestions would be very much appreciated!



Thanks so much for your help,
Chris


----------



## Homerepairguy (Aug 1, 2010)

cjdavia said:


> Some joists are not level by about 1/8"-3/16" between adjacent joists. The joists are 16" apart. In other words, one side of the joist bay might be 3/16" higher or lower than the other side so when I lay the decking down there can be a 3/16" difference across the 16" inches. And then maybe another 1/8" difference to the next joist over the next 16 inches. The joists themselves appear to be pretty much level across the full 18' length of the joists.


Hi Chris,

A few things:

1. With an 18' span, is there a supporting beam in the middle making each span 9'? If so, are the high joists resting on the center supporting beam? Or maybe you have two 10' joists sister-ed together over the center supporting beam?

2. What size joists?

3. If 18' long joists were used (long single length, not two 10 footers sister-ed together), to fix your problem, I would get fairly straight, not warped PT 2x4's and screw them to the sides of the joists using stainless steel, hot dipped galvanized or ceramic coated screws. At 16' to 18' long, the 2x4's should be easily bendable enough to end up with almost perfectly straight and flat surfaces. I wouldn't use glue or nails in case adjustments need to be made years down the road. ..... With that in mind, I would put the screws down just far enough to be able to remove the screws later from below without having to remove all of the decking boards (assuming that the deck is high enough to go underneath.) If not enough room to go underneath later, then screw placement would be a non-issue.

Personally, I think 1/8" or more difference between adjacent joists 16" apart will end up with a wavy look. If all of the joists were installed crown up in one perfect plane, then the high joists would settle down on to the supporting center beam over time, ending up with a flat looking deck. But with all of the planing and shimming done so far, that option doesn't seem like a possibility anymore. 2x4's screwed to the sides of the joists seems to be the easiest solution now.

HRG


----------



## cjdavia (May 28, 2010)

HRG,

Thank you for your thoughtful response. 

There is one triple beam about 16' away from (and parallel with) the ledger board. The joists are 2x12 and they are full 18 footers.

I think you are right, even 1/8" might cause an issue. When I get the delivery I might lay out a few boards in the worst areas to see just how bad it is. Sistering with 2X4 sounds like a completely reasonable approach. 

Thanks again!
Chris


----------



## Homerepairguy (Aug 1, 2010)

cjdavia said:


> HRG,
> 
> Thank you for your thoughtful response.
> 
> ...


When you get delivery? I thought the joists were already installed. I must have misunderstood.

EDIT: Just realized that your delivery must mean delivery of the composite decking material. If there's only two low joists, maybe just sister long 2x4s on each instead of trying to raise the joists or shimming.

Best regards,
HRG


----------



## hand drive (Apr 21, 2012)

tolerances for treated lumber is quite high, 1/8" is nothing to worry about but 1/4" to 3/8" would be of concern.


----------



## kwikfishron (Mar 11, 2010)

+1 to hand drive's responce. I think op's overthinking this a bit. 1/8-3/16" is nothing in the middle of a 16' span, they'll flatten out. As long as the joist are in plane at the hangers they should be fine.


----------



## cjdavia (May 28, 2010)

Sorry for the confusion. Yeah, the joists are already in place with hangers and what I think are hurricane braces. 2 of them have to be raised about 1/8". 

I agree that sistering is probably the way to go. 

The composite decking material should arrive tomorrow. 


I'll let you know how it turns out and thanks for all the help!


----------



## cjdavia (May 28, 2010)

thanks everyone


----------



## cjdavia (May 28, 2010)

Thanks for all the advice. I really appreciate your help and will most likely be planing and sistering over the weekend but please let's keep this simple: 

If I lay capped composite down with hidden fasteners across joists that are not perfectly level, will there be a noticeable wave? That's all I am asking.

Let's say the first joist is our reference, the second joist is 3/16 higher than the first and the third one is 1/8 lower than the second. 

I want to know about your personal experience. Have you ever put down composite in this type of circumstance? Do you wish you planed and shimmed the joists more carefully or glad you did not expend the effort?

Thanks so much!


----------



## kwikfishron (Mar 11, 2010)

cjdavia said:


> Thanks for all the advice. I really appreciate your help and will most likely be planing and sistering over the weekend but please let's keep this simple:


I think you should re-read post 10 and 11.


----------



## ChuckF. (Aug 25, 2013)

I assume you are using typical metal joist hangers. On the joists that are low, I would try hammering a cedar or plastic wedge (Home Depot) into the bottom of the hanger, between the saddle of the hanger and the joist. That might be enough to move the joist up a fraction of an inch or so.


----------

