How to tile under a forced hot-water baseboard heating

Insufficient space under one of the baseboards for backerboard and tiles - read on ...

I am replacing bathroom vinyl floors with tile. Under the vinyl is a base layer of plywood, and then a second layer of plywood. There is no luaun on the second layer of plywood. Whatever adhesive was used between the plywood
and vinyl comes off easily with a putty knife.

I only have access to the subfloor 1) where I cut a 1’x1’ hole in the wallboard years ago, and 2) where I pulled up the vinyl some to see what the subfloor looked like.

At the hole in the wall, the wallboard sits down along the side of the top subfloor on another piece of plywood. This is all I can see of the first layer of subfloor.

My guess is that when the house was constructed (1978), that there was a rough plywood floor in the bathroom (thickness unknown), the wallboard was installed, and then a second layer of plywood (measures 1/2” thick) installed running from wallboard to wallboard.

A local tile place I spoke with yesterday recommended the cement backboard. Her comment was that here in NH, the plywood subfloor would swell and contract; that this could cause the grout (and possibly) tiles to crack.

I also measured under the heating fins for all 3 bathrooms that I will tile. The space under the baseboard for 2 bathrooms is ok.

BUT for one, the bottom of the heating fins is only 1” above the vinyl floor. There is no give (vertically) on the forced hot water pipe to pull it up a bit. And the front cover is a tight 7/8” above the vinyl floor. After putting down backerboard and tile, there would be 0” left for air circulation. The heating fins would be sitting right on top of the tile, and the front cover would not go back on. ARG! So what to do???

Joists are Unknown wood, but in good condition, 9.25 inches tall, 1.5 inches wide, 14 inches on center, and 10 feet long between supports (a guess).

Thanks, Joe

 

I guess lucky for me all 3 of my bathrooms had space under the water baseboards for tile.

I'm pretty sure I understand your issue. The best and probably most inconvenient solution is to raise the heating elements up so you have room.

Another option is to not use cement board and use something a bit thinner like schluter ditra maybe?
http://www.schluter.com/6_1_ditra.aspx

Or the least recommended method would be to just install the tile directly over your vinyl if it is glued down very well and your subfloor/joist situation is solid.

I guess it also depends on how thick your tile is if the previous 2 will work. Good luck.