Toilet flange mount to subfloor or LVF?

Old 10-24-19, 06:05 PM
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Toilet flange mount to subfloor or LVF?

Hi all,

I keep reading that it is "best" to install a toilet flange to the finished floor to reduce the seal to the toilet. I just repaired the PVC for my toilet drain, which is essentially a 3" 90 elbow with a flange in it. I haven't cemented the toilet flange in yet, but I am wondering if it is best to wait on the flange and install it over the finished floor, which will be LVF.

I am guessing above the floor is better but I also read that most flanges are on the subfloor just because the finished floor isn't installed when the work is done.

That said, LVF isn't that thick, and I intend on using a Sani Seal which I am guessing can accommodate the thickness of most LVF. They can also be stacked, but I don't think I would need to.

If I were to cement and attach to the subfloor, that elbow sits just below the 3/4" subfloor, so I would get about 1" of PVC into the elbow to cement. Is that sufficient? Or, should I come out of this elbow with the tiniest bit of 3" pipe, and use an "over 3 pipe" flange? I imagine if I mount the flange to the finished floor, I definitely need to extend out of the elbow a little bit. What's the minimum amount of PVC that should touch in a connection?

Old 10-25-19, 04:09 AM
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You don't want the flange above the finished floor surface. You want it even with the finished floor surface. If you it have above, the toilet will be sitting the thickness of the flange above the floor surface. But you can get away with up to a 1/4 in above or below the floor finished surface.
Old 10-25-19, 04:55 AM
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I agree, you do NOT want the toilet flange on top of the finished floor. I have seen some toilets where there sealing ring is very close to the bottom of toilet. With the flange on top of the finished floor it may sit too high for some toilets. If the ring is lower the extra height can always be made up by using jumbo wax rings or toilet flange extenders. I install toilet flanges on the subfloor with a clearance cutout in the backer and tile.

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