Hi,
I am in the process of deciding how to install a radiant heating system over an existing concrete slab. I have seen articles and information on pouring new slabs and thin-slab systems over wood sub-floors but nothing on putting a system over an existing slab. I have enough room that I could pour a thin-slab (1 ½ to 1 ¾ thin) over the existing slab. I plan on tiling the room. The room is approximately 15 x 20 ft. I do not want the tile to crack and I am not sure if I need to put a barrier between the existing slab and a newly poured thin slab. Also should the thin-slab be concrete or gypsum based system. Or would I be better off with another alternative since the existing slab is not insulated? Does anyone have any experience in this area?
Thanks
Replies
If your concrete slab is quite level and you can afford a 3" rise in floor level, I would do the following:
1) Lay down a poly vapor barrier over the whole floor, 4 mil or heavier.
2) Lay down 2x4's on the flat, with 14 1/2" inches between each 2x4, shot down with a Hilti or Ram Set.
3) Fill the space between the 2x4's with 1" foil faced rigid insulation, fitted tightly with the foil face up.
4) Install two loops of 1/2" pex in each 2x4 bay on top of the rigid insulation.
5) Put down 3/4" T&G plywood or OSB, glued and screwed to the 2x4's, being extremely careful to screw into the 2x4's, not the tubing.
6) Put down a layer of 1/4" cement board, glued with thin set to the plywood.
7) Tile the floor and enjoy.
This is assuming you know how to do the radiant floor heating, ie hook up to the boiler, mixing valve, etc.
One other consideration, if the pex tubing is more than 1/2" OD, then you may have to rip strips of wood to build the 2x4's up somewhat - 1/4" or so.
I have done a similar job which worked out fine. Any questions?
Bob
Bob,
Thanks for the information. I don't think I can afford a 3" rise in level. If I went with a thinner profile do you think it would work?
I believe I got the boiler & mixing valve stuff figured out. I just a installed a new hot water heating system (boiler, DHW & controls). I may have some questions in the future on interfacing my Tekmar boiler controls with the mixing value controls.
Ron
What about using bubble foil insulation with the seams taped, then 1x sleepers(tapconed)12"oc, 5/8 subfloor(glue and screw), 1/4 backer and then tile?
I think 3" is about the minimum for a good job. If you don't do the 1" rigid insulation, I think you will be wasting a lot of heat into the existing slab. I have a friend who has the light weight concrete under tile and he would never do it again.
I think you might be better off with baseboard radiation around the perimeter - at least the room will be warm, even tho the floor is a little cool.
Bob
"I have a friend who has the light weight concrete under tile and he would never do it again."
Bob, what doesn't he like about it? I'm looking to do something similar on my 2nd floor. 2 bedrooms & a bath. Carpet in bedrooms and hall, tile in bath. Just wondering. Bear
Bob,
Your outline is nicely explained. I have a similar situation I'm trying to layout but I'm intending to use a little different approach. I'll highlight my differences by referencing the steps you have suggested in your post.
(Step 2) I am planning to use trex or a similar plastic material to avoid any possible moisture problems such as rot, bugs etc.
(step 4) Rather integrate pex tubing into step 5
(step 5) Route out tubing runs into the subfloor to accept the Pex. Lay the Pex into the subfloor similar to quicktrack (a wrisbo product)
Just another approach-John
Edited 2/14/2003 12:57:22 PM ET by john m