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How to get thinner floors?

Tremolux Member Posts: 28
We have three 1st floor rooms that we want to convert to radiant floor heat. The house is being restored, with the remaining hot water radiators being replaced with low-water Euro units. ( most of the cast iron was broken, but the pipes hold pressure )

One is a bedroom, where the original wood floor had to be ripped up exposing the subfloor from 1930. The bathroom was gutted for minor enlargement so the subfloor is gone ... bare to the joists. The kitchen floor is old linoleum tile, over plywood, over subfloor.

The plan is to do radiant heat & tile floors in all three, but matching to the existing floors seems to be a problem.

One prospective contractor suggested using rock-board, or Hardie-board, or a similar product over the pex panels on top of the subfloor ( instead of floating in a layer of mix ) and then attaching the tile to that board. Would that work? 1/2 in. board minimum?

Would we be better off tearing out the rest of the subfloor and starting from the joists?

The kitchen has two outside facing walls ( brick ), plus a large window ( being replaced with a double-pane ), and a porch door with 12 glass windows ( plus a storm door ).

There might not be enough floor to heat it with radiant one the cabinets are installed, minus the space under the refrigerator.

Comments or suggestions are certainly appreciated.


  • Thinnest Floors

    Subfloor + 1/2" Quik Trak (an Uponor product) + cement board + tile

    You will have to lower the water temperature for radiant via a mixing valve and pump.  Your contractor will help you out.

     Do you have a basement or accessible crawlspace under the first floor?  If so, an alternate method is to install tubing with plates attached to the underside of the subfloor.  It's not as good as the above method since the tubing is further removed from the conditioned room, but it is an alternative.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Jack
    Jack Member Posts: 1,047
    I did all three of my bathrooms this way.

    You are so far into it that i can't imagine that you wouldn't want to open the sub-floor and get to the floor joists. In all three of the bathroom remodels in my home I did this and went to the rafters, studs, joists. I was ale to repair concealled water damage, and in a house as old as your there is likely some there. I was able to plumb the walls, level the floor and get things square with the world again. Doing so will also open the possibility of moving fixtures.

    I went with a 3/4" plywood, Uponor Quiktrak, 1/4" cement board and then tile. I made an Oak threshold into each bathroom, for the rise, but two year into it, no one has fallen into the bathrooms. It has about 1 1/4" rise. That is a lot, but it has not been a problem. A thought, depending upon what you have for floor joists, if they are heavy enough you may be able to shave the top off and depress the floor level a bit reducing the differential.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    If you are tearing out

    the sub floor you could use a staple up system with aluminum panels. I thought Viega climate panels were the thinnest radiant heat on the market.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • timbus
    timbus Member Posts: 3
    how to get thinner floors

    Viega Climate panel and Wirsbo quick trac are the same thing. Both 1/2" thick, and very efficient. Made by Stadler originally. Rehau Raupanel is a bit thicker, 5/8" but a better heat transfer product. Also, can add to the structural strength a bit.
  • pipemd
    pipemd Member Posts: 3
    Radiant and floor height

    here are your options.

    1- Use any of the track systems for 3/8" tube which will add 1/2" to the height.

    2- Install 3/8" staple down (no tracks) and float  Gypcrete over the tubing.

    3- Install electric radiant  and pour a self leveler over it to embed the tubing.This will add 1/4" to 3/8" inch. Flextherm makes has nice products.

    4- Install staple up radiant tube on the underside of the subfloor.

    For #2 and #3, install an anti fracture membrane to keep any movement from transferring upward and popping tiles loose.
  • tim smith
    tim smith Member Posts: 2,743
    Another option

    But is a bit of a pain. We have had the GC pull the subfloor, install 2x blocking on edges of joists down 3/4 from top and inset plywood panels between joists for sub floor. Then either Quicktrack or mudset  depending on thickness needed. This saves the 3/4" of subfloor that would normally be on top of joists. Just a thought. Tim
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