Decking over a tile / concrete slab

[Ethan Brown]

First time poster and not a builder. Just wondering if the below is possible:

I want to deck over our front porch (~1m x 4m). The porch is currently tiled over a concrete slab. I was thinking of laying joists over the top and then decking on top of that; however, I was wondering if you can lay joists down so they aren’t as tall? I understand that this will make the deck less stable in a normal circumstance, but will this be the same as the concrete slab is already there? If I have the joists standing upright then it will be too tall for our entry way.

Thoughts?

[Ed Pawlowski]

You can but you may regret your decision down the road. Sealing. staining, whatever, wood deteriorates over time

Wood is more maintenance than tile or stone that is easily washed off. You are going to have a couple of inches of space between decking and the base. Rodents and insects like places like that. Of course, it you are raising rats for research labs it is a great place for them to nest.

[trader_4]

Yes, since the slab is supporting the wood, the joists do not have to be as wide, even a couple inches would be enough. You can anchor each joist to the slab in a few spots for stability, keep them from moving, etc. I hope it has some pitch in the right direction so water doesn't pool up under there.

[trader_4]

Nowhere for water to drain? It accumulates, freezes? IDK, might work but I think using some wood strips is safer.

[Hal Bundy]

Maybe throw in some grass accent tiles as well?

[hubops]

I wouldn't call them joists - more like levelling strips or spacers. Why not synthetic decking directly on the tiles ? John T.

[Dean Hoffman]

Maybe the OP could run the joists to allow for water drainage if he doesn't care how the deck boards are run. I was trying to think of an alternative to wooden joists depending on how much higher he wants the deck to be.

[Hawk]

Way to tell him why and the proper method, pea brain. Do you offer anything of use being in here?

[Hawk]

Wood directly on concrete will deteriorate and eventually cause the deck to slowly collapse. You should have a few inches between if possible. Use composite or galvanize spacers between the two. It will keep the moisture and all drained water from contacting the wood and allow airflow under them.

[Ed Pawlowski]

Maybe a synthetic 2 x 4 is the best of both worlds. Won't rot and allows air circulation.

Depending on the size, I'd consider building it in sections that can be lifted for cleaning the gunk building up underneath.

[Ethan Brown]

Thanks for the reply. I can see how the water could be an issue. What if I attached the joists to the concrete with angle brackets? Would this keep the water off the wood and allow for it to flow out naturally? It is underneath a roof and generally doesn’t get much water as is, but better safe than sorry. Cheers

[Ethan Brown]

Hi John, I am planning on using a synthetic decking but was not aware I could do this straight into the tiles. How would you suggest going about this?

[Ethan Brown]

Hi Trader, do you think anchoring each joist would allow enough space between the joist and the slab for the water to escape? Cheers

[gfretwell]

I think I would use 1 1/2"Trex for the sleepers under the deck. They won't rot any time soon. That isn't going to be at the Home Depot but a real lumber yard will have it. Run them up and down the slope, not across it so it can drain. If you can't find that stack a ribbed

5/4ths Trex on the bottom and put a standard 3/4" trex or even PT wood ion top of that. Use some 1/4" hardware cloth at the bottom so water can get out but rodent's can't get in.

another option; If you are near the coast, a marine supplier can sell you rough sawn

0.8 CCA lumber that will outlast us all.

[micky]

+1

Interesting how you and Bob F didn't get a reply from the OP. I guess his mind is made up.

[Ed Pawlowski]

I saw a message, "I admire your honesty" until you are honest with them and then you are an asshole.

[Ethan Brown]

Hi Ed, sorry I am really new to this type of thing. What do you mean by a synthetic 2 x 4? Thanks for the thought on the gunk building up underneath, something I hadn’t considered. I am just trying to understand how to keep the wood off the concrete slab and what approach would be best? Cheers

[Ethan Brown]

Something like this underneath the joists?

[Ed Pawlowski]

Right, synthetic

Even pressure treated on concrete will deteriorate over time. Depending on cost and height needed you could double up on Trex.

If you plan to move in five years, most anything will work but if it is long term, go for rot proof.

[Clare Snyder]

frame around the concrete with upright 2X, lay strips on top of the concrete, separated from the concrete with a membrane - roofing paper or whatever, then lay the decking on top. about 1/6 of my front porch is constructed this way over the original pre-cast "stoop"