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ssc 04-07-2006 04:19 PM

wooden platform on concrete
i want to build a wooden platform on top of concrete. i was told to 1st put down plastic so the wood does,t rot out. do i need to use pressure treated wood(2by6) or can i use regular (2 by 6 s ) . i was just going to lay down the 2by6 flatevery 4 /6 inches qnd go over it with 3/4 plywood putting screws 2 inches. it will be covered with a building but not heated to hot. i live in get very cold in the winters. will this warp or will it stay pretty flat that is my main concern , flatness

tgeb 04-07-2006 07:54 PM

I would not put plastic down, but I would use treated lumber. The plastic can not only keep moisture away, it can also trap moisture around your lumber. Don't forget about insects that would like to eat that lumber. Go with the treated. You could probably use 2X4 lumber though from what you have described. Might be cheaper.:)


bob the builder 04-07-2006 08:03 PM

I opt for the treated, but I'm sure in some parts it is allowed to use s.p.f. If you use treated make sure it is dry enough so there isn't excessive shrinkage after installation. This may take several weeks depending on moisture content...


ssc 04-08-2006 07:54 AM

so just put the treated lumber on the concrete with nothing under it.

tgeb 04-08-2006 09:58 AM

You got it!

You might consider putting some kind of venting so it can breath a little under there, so moisture if it does get under will not cause problems later on.


747 04-08-2006 03:40 PM

A rule of thumb is always go with PT lumber when its in contact with cement. Also if your thinking about painting the platform you must wait a considerable amount of time before preceeding.(months)

Darylh 04-09-2006 10:21 AM

I would at least put tar paper down before the pressure treated wood and 2x4 every six inches will be extremely strong.

Bonus 04-09-2006 10:15 PM

Why would you want 2x4 more frequently than 16"o/c? Unless you've got some nasty point loads 3/4" ply can easily span the remaining 12-1/2". Ventilation under there is going to be an issue, if it gets, and stays, moist, the plywood will rot out on top of the pt sleepers. My $0.02

Darylh 04-10-2006 09:21 AM

I built a huge sunroom about 8 years ago and what I did(code requirements) was I layed tar paper all over the concrete slab then layed 2x4s flat 4 feet on center then ran 2x6 16 inch on center. I put a 2" plastic soffitt venting around the outside nailed to the but ends of the 2x4s. In your case your wanting to run just 2x6 on flat so the soffitt venting should work the same just make sure it all flashed properly..

ssc 04-11-2006 03:14 PM

you didn't use pressure treated wood

Darylh 04-17-2006 09:02 AM


Originally Posted by ssc
you didn't use pressure treated wood

Yes I sure did I also used 3/4" t&g select plywood and
talk about solid as a rock.
I also Insulated the floor to but I made up some wooden
blocks to keep the Insulation off the concrete and create some air flow.
What goes through my mind is when ever building a floor on a concrete slab
there is not going to be any excess to it so build it extremly strong,
insulate it ventalte it and use the very best in Material
then you won't ever have to worry about it later.

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