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The bathroom model saga continues. The old toilet flange was rusting, and the subfloor was rotting, so I pulled up the subfloor around the toilet, and replaced the drain pipe with ABS, and an elbow. The plan is to tile this bathroom.

So my question is- should the toilet flange sit on top of the backer board so that the top of the flange is close to flush with the top of the tile? Or should the flange sit on top of the tile (thus raising the top of the flange 3/8" or so over the top of the tile)? I've seen it recommended both ways, but have had some trouble finding the pros/cons of each.

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4 Answers 4

up vote 6 down vote accepted

You want the flange to be secured to the floor as tightly as possible. If it's on top of the tile, I think you run the risk of cracking the tile when you're tightening the nuts on the flange, so I say attach it to the backer-board.

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In the process of redoing my vinyl floor with backer board and tile. The flange is set on the finished vinyl floor as shown in the upper photograph. The result is a toilet that rocks,leaks at the wax gasket and has ruined the vinyl floor. It's not a cheap Home Depot toilet (can't remember the brand, but it was about $200 years ago...). Even after removing and replacing the wax gasket, then doubling it up with the plastic collared type and wedging the toilet front and back at 4 points, it still rocked and leaked. The same is true of the same model toilet in another bathroom. I will be mounting the flange flush with the new tile floor and using a rubber (foam) style gasket this time.

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The toilet flange needs to be on top of the finished floor. Meaning the bottom edge of the flange needs to be on the same plane as the toilet. So if your toilet sits on the tile, the flange needs to be on top of the tile too. The spacing of the toilet exit "horn" and sealing surface is designed for this height.

almost all plumbers agree, here are some sources:


cutaway of toilet to flange spacing

if you have it lower than the finished floor you risk leaking toilet water (the water is the best part) into the floor or worse, in-between the tile, sub-floor, backer board. This is because the wax ring was designed only to take up the air gap, not to provide a "tunnel" or extension of the pipe/flange/toilet horn.

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I wouldn't recommend installing the flange on top of a finished floor like tile since that flooring may not be as stable as the subfloor (and you could crack the tile). But you can get a flange extension ring to bring the flange up to the finished floor level. –  BMitch Feb 28 '14 at 4:04

When I redid my bathroom (added backer board and tile to replace linoleum) I had to raise the flange too. All I did was cut a piece of plywood to fit around the flange and raise it about the same as the backer board. I agree with Niall C.'s answer not to put it over the tile since it could easily crack but I also think the backer board would break easily too considering the screws for the flange would be very close to the edge of the backer board.

But in my case, I didn't realize that I needed to raise the flange until after the tile was in and a piece of plywood worked really well in that situation. :)

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Good point about the backer board. +1 –  Niall C. Aug 20 '10 at 1:50

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