I have just finished a 20x 18 sunroom. I had a plunber come in and install under floor joist heating system off my existing hot water furnace. This new room is going to be tiled.
The problem that I now have is that the contractor that built the addittion did not match the new room to the exisitng sub floor. The existing tile floor and the new addition floor is aprox. 1-1/8 difference in height. I know that you have to put down cement board before you tile, but my question is instaed of installing more wood to raise the floor to what ever height I need for my tile & cement board to match the existing tile floor, is there some sort of material (like cement or floor leveler) that I can put down and my floor heat will tranfer to the tlie effeciently? I feel that if I install 3/4" plywood ontop of the plywood that is there now and then the cement board,my heat will not transfer to the tile effeciently.
I hope I am not to confusing.
Thanks, TAZ

Whatever difference there might be between a cement fill and plywood would be slight, and neither would affect the heating of your room. The only thing that might be affected slightly is the response time. Look at it this way, the heat is maintained by the mass of the flooring, and all you'll have is a little more mass. So, the room MIGHT not heat up as quickly (like it might take five minutes longer to reach temperature) but it won't cool off as quickly, either. I wouldn't worry about it.

I agree with Richard.

So if I understand correctly the new floor has to come up an inch+ higher to meet the old floor.
The buildup I would want for tile would be to add another 1/2" of BCX or ACX grade plywood, no CDX allowed as the "D" layers have to many voids which could create compression problems for the tile down the road. And, CDX is not rated as underlayment by the APA - American Plywood Association, it carries only a sheathing rating. Orient the new ply 90 degrees to the run of the existing, screw the 1/2" into the existing layer of ply but try to miss the floor joists so the second layer can remain isolated from joist movement in the future. Make sure there is NO seam over seam and that the new seams are about 4 to 6" off the existing ones. Fill the 1/8" gapped seams of the second layer with a cheap latex caulk and keep the boards off the wood framing in the wall by 1/4" so if the wood in the wall swells with seasonal weather it wont push on the plywood causing it to buckle.
Now install 1/4" cement board over the ply embedding it in a bed of thinset combed with a 1/4" square notch trowel ( the caulk mentioned above keeps the thinset from filling the 1/8" gap in the ply). Anchor the cement boards with 1 & 1/4" galvanized roofing nails or backerboard screws ( I personally use an air nail roofing gun).
Tape all seams of the cement board with fiberglass mesh tape and coat with a thin layer of modified thinset using a 4" or 6" spackle blade. This will unify all the cement boards. Now you are ready to tile, using modified thinset to set the tile.
Well almost, first tell us what the size and spacing of the new floor joists and what is the length of their unsupported span. Based on your answers I may have to change some things mentioned above.

TO do the tile install right and by the book, so that your tile floor lasts as long as the rest of the house, all that I described above should be done. Thias has all been verified by the Tile Council of North America who conducts test in asssociation with tile materials manufacturers to determine what does and what doesn't work, and within what tolerances it will work. A lot of guys who install tile will have no idea of what I am talking about, either because of indifference toward the trade or they are happy to work as hit and run artists who dont care about the finished product they produce. A tile professional will want to do the job right to perpetuate the trade.

Thank You.
I understand every thing you said except nailing the 2nd layer sub floor. I always thought that you should screw it down to the floor joist. The problem that I would have if I am not to screw it to the floor joist is the flex tubing that I have for the floor heat is iside each bay.

Thank You,

if there was a change in plane
why didn't you install a layer of 3/4" ply
then put your heating system and tile over

now, you can do a mud pack

Matt
Cupan Custom Tile and Paint
tile contractor

The contractor said this was a better system. If a pipe breaks you at can at least repair it.
They just did not measure properly for the hieght of the existing sub floor.

I still do not understand why you should not screw the second sub floor to the floor joist.

quote:

Originally posted by Taz:
The contractor said this was a better system. If a pipe breaks you at can at least repair it.

Every contractor is going to have a different opinion here. Personally I think the heat loss and uneven and inconsistant heat is more of an issue than a pipe breaking. That tubing is constucted knowing that it has to be durable because usually it will never be seen again once under concrete.

I know it is too late now but for informational purposes, we have been setting the tubing on top of the 3/4" subfloor and then pouring an 1 1/2" high strength concrete on top of that. Then we go below and spray 2" of polyurethane closed cell foam to direct the heat upwards. Of course your floor system has to be designed to accomodate this - I've been told it's no more expensive, but the truss designer needs to factor it in anyway. The beauty of this system is it gives you a more even and and consistant heat as the principal of thermomass will be present in concrete. You can then lay flooring on top of the cured concrete.

no need for the foam

heat rises