Redecking bridge

[EddieWalker]

I've never seen treated wood that is T&G before and was surprised that it's available. I've been trying to figure out where it would be used without any success. I would not use it for any sort of outdoors decking. You need the water to drain through the boards as quickly as possible. You also want air flow all around them. Both are important for longevity.

With the span that you have to deal with, and the process that it takes to create pressure treated lumber, you are going to struggle to find anything that will remain flat long term. If I was to do anything, it would be to run a board under the decking, centered between the I beams to tie the decking together.

Why 2x6's? If you run the numbers, I think you will find that when comparing how many square feet you are covering, you'll find that 2x8's will cost you the same as 2x6's. I prefer 2x8's because they are just a little more stable and you have fewer boards to handle.

Eddie

 

[tlj87]

2x6 was the only size available in PT T&G. I was considering the T&G because I thought it would be more rigid because of the interlocked decking, less bowing, warping etc. It sounds like the general consensus here is to definitely not use T&G. 2x8 is on there now, each plank is a little over 5' (1/3 of 16'). I would like to go to 7 (1/2 of 14') or 8'. If I attach at top of the I beams, center of bridge between I beams and then at the curbs (perhaps 4x6) at each side, I think that would greatly limit bowing, warping, etc.?

 

[s219]

The biggest issue with PT wood is warping and twisting as it dries out (which may happen even before you get to use it). You can get kiln-dried PT (called KDAT for "kiln dried after treatment") but the cost is more of course. In some situations, it's justified if it saves you on labor or fixing boards later on.

For regular PT wood, I have gotten in the habit of keeping it stacked and strapped carefully before use. Then when putting into use, making sure it's nailed/fastened properly and quickly (i.e., no partial jobs to leave a board dangling un-restrained out in the weather). Since then I don't have a lot of problems.

In some cases you can't always nail/fasten/brace it securely enough though, and it's prone to warping or twisting (for example, a long horizontal deck rail). You just have to hope for the best. Don't underestimate the ability for a single board to warp/twist and take all your bracing or attached pieces with it. Seen it too many times. There is a lot of torque in a piece of lumber as it warps and twists.

So I have two suggestions -- first look into KDAT and see if the pricing is feasible for this project. Second, buy regular PT lumber and stack it with spacers ("stickers") for a few weeks in a dry location, strapped and/or weighted down, so that it can dry out and stabilize before use. If any boards are hockey sticks when they come out of the stack, return them to the supplier.

 

[SandburRanch]

Check with your county road maintenance department. Sometimes they replace bridge flooring lumber that's still plenty good for your use. I bought 90 2-1/2" x 3-1/2" x 16 ft. creosote nearly 40 years ago and have used them for everything from A-Z including corrals.

 

[oosik]

I re-decked my back porch last year. The only PT lumber available locally is that slime green colored stuff. So I went with standard kiln dried 2 X 8 lumber and put my own preservative coating on it. The previous decking lasted 32 years and actually was in good enough shape that I have saved it for another project.
If you go with T&G and no spacing - the deck will surely develop mold, slime etc and rot out fairly soon.

 

[beeforty]

Definitely go with something that gives you air space between the boards. When I redecked my bridge I drive over, I left 3/4" at least between the 4x12's to be able to clean out the leaves that fall. Also I wouldn't want too much room out side of the beams to drive on for fear they might start snapping off.

 

[rtimgray]

I would vote for leaving a space between the boards. Or even butting them together during installation, and the natural "shrinkage" will usually leave a little gap.

A couple of years ago, SWMBO was looking at our back deck (about 3 years old at the time) and she didn't like the gaps between the PT decking boards. She asked how big of a deal it would be to pull them up and push them all together. I told her it wouldn't be too tough, but it wasn't a good idea because it would cause water to stand on the deck.

Long story short, I pulled up all of the decking, pushed it together, and even had to add a couple of boards to make up for the gap spaces.

Worst idea ever - and I can't even say "I told you so" - not if I want to still sleep indoors. Several of the boards have warped, twisted, bowed up, etc. due to having water standing on them at times and poor air circulation. One of these days we are going to re-deck - again - and she has agreed to leave some space between the wood.

If it were me, I would leave a little space. If you are worried about bowing in the middle, I would think that you could run some PT 2x4s underneath the decking as you install it (or after, if the bottom of the bridge is accessible) and screw the deck boards to those. It would serve as a tie to keep them together.

I would also go ahead and make it wide and just put a board perpendicular to the decking boards along the edge. Nothing that you have mentioned driving (or walking) across the bridge would cause too much of a canitlevered load anyway.

Good luck and take care.

 

[rd_macgregor]

When I intalled the 6' deck on my bridge, the PT 2x6's were 12' long, so I had to cut them. Before intallation, I dipped both ends of each deck board in a pail of wood preservative. The PT treatment often doesn't penetrate to the center of the board so a cut end is especially susceptible to early rot.
The shrinkage of wet PT wood is incredible; I intalled the boards a finger-thickness apart, but the gaps are considerably wider than that now.

 

[KennyG]

When I bought my house, the cedar deck had been installed with no gaps. After the first time someone fell through the deck I replaced it with an composite Azek deck.

 

[smilindave]

I have used the PT t&G 2X6 as a retaining wall. Its not too bad to work with as long as the wood is still wet. However, the tongue and grooves are not very pronounced and I do not believe it will give you the extra strength you are looking for.