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Question DetailsAsked on 12/22/2017

can I attach a closet flange to the subfloor and not to the down pipe

old flange fell apart and leaked water, damaging subfloor. I cut out damaged portion and replaced with new plywood. Old flange appeared to be setting on top of that but disintegrated after 24 years. The 4" drain down pipe has a pvc sleeve extending down the outside. New pvc press-in alternatives like Sioux Chief seem to make the toilet sit too high off the floor so I am looking to install just a metal flange screwed directly to the subfloor but not attached to the drain pipe, and then using a wax ring and bolting down the toilet. A test fit seems to show that the height is about right, and I can shim any little gaps to make the toilet level.

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Sure you can - but expect it to leak through surface tension wetting and wicking (which will likely cause rot and urine smell in the subfloor) as well as possible sewer gas leakage through the gap between the two pipes (the flange and the pipe) - not to mention not anywhere near to code.

The existing PVC sleeve does not sound good - sounds like maybe it leaked in the past and that was a rube goldberg fix, and if it is used to retain flushed material provides an over-sleeve leakage point further down where the PVC ends too - assuming the DWV piping is not PVC with them cemented together. I would fix it right - either by cutting back the DWV pipe to the right stickup height and putting a new flange on top (best), using a closet flange repair ring like sioux chief and other make if a major portion of your flange is intact (like just one bolt opening broken out), or in a more "bubba" type fix, cutting a 1/4" plywood shim sheet (under entire toilet with hole for pipe) of marine or at least treated plywood to raise the toilet a bit so the flange fits right under the toilet, then caulking that shim around the base of the toilet - though that is a poor substitute. There are also commercial plastic shim plates to raise a toilet 1/4" or 1/2" which fit under the base of the toilet, and you trim the outer edge as necessary with sheet metal shears or utility knife to a hair under the outside toilet dimension, then caulk the gap between floor and toilet.

One other thought - have you GENTLY pushed on the DWV pipe - it might be it is flexible enough (if plastic) or loosely enough mounted that with a bit of weight from the toilet it will actually press it down to the right height - might just take a few pounds to press it down to a good fit. Obviously, you do not want the whole toilet/person weight sitting just on the pipe 9plus that would high-center it) and you need some room for the wax seal so it is not all squeezed out.

Note you talked about "shimming any little gaps to make toilet level" - toilets do not do well with spot shims unless you use a lot of them - the base flanges crack off easily if the toilet is not firmly supported fairly uniformly all around, plus small shims smash down or work their way out, resulting in a cracked toilet or flange. Again - do it right.

Toilevator and Oatey and others do make snims designed to raise a toilet up - some just a fraction of an inch, the Toilevator and similar medical ones are designed to raise the toilet to a more convenient sitting height for elderly and disabled people so raise it an inch or more commonly. Goolge "toilet shim" for examples and blogs from Terry Love and others sbout shimming a toilet up due to too high a flange or rocking.

The slip-in type adapter flanges or combination flange-wax seal replacements have a reputation for leaking, and also reduce the ID of the DWV drain pipe by 1/4-1/2" ID - not a big thing if you have 4" DWV under the toilet, not so good with 3", definitely a no-go with 2 or 2-1/2" found in some older hosues. But the sleeve type ones tend to promote clogging, both because they are a reduction in passage size (a no-no in DWV work), but also because they usually have a squared-off flange or collar which can catch soilds and start forming a blockage. Another pair of problems with the press-in type insert flanges - in addition to the flange being plastic so they can easily snap apart if the toilet starts rocking a bit, is the flange is not a rigid fit in the DWV drain line so it provides no vertical support to the toilet so can cause opening up of the wax seal. Also, if you wever take it out, it is common for the gasket to stay in the pipe and then fall down the pipe and form a clogging point - though taking care to wad a rag down below the bottom of the flange extender before working on it can stop that and leave it hanging within easily removeable reach.

I would do this so you hopefully have peace of mind for some time to come, and get the old flange off and a new one put on at correct mounting height - which may require cutting the existing DVW pipe to fit.

One other tip - if the flooring is sealed around the DWV pipe penetration so any leakage will not run down there, and even sometimes even if not sealed, a lot of old-timers leave a small gap in the caulk seal around the toilet base, at the center back, so if there is a leak at the flange/wax ring it will hopefully appear behind the toilet on top of the floor before it starts rotting the fllor like it did in your case. That is one good reason to run the flooring (sheet or tile) in under the toilet and sealed with a raised seal around the DWV pipe - to keep leakage out of the flooring and have it rapidly appear on the floor behind the toilet rather than saturating the subfloor and rotting it for sometimes many years before you discover it.

The water-seal and handling of any leakage under and behind toilets is an under-designed area - not hard to handle, but takes thinking about where it can leak (at flange, wax ring, tank gasket, tank bolts, fill valve tank penetration) and how to get and keep that wster on the floor where it can be seen before it gets out of hand, rather than running down into the subfloor (and maybe through underlying ceiling) and/or in under adjacent vanity and/or walls. Ditto for shower/tub splash or dripping of people getting out of the shower/tub, which commonly run downs at the floor/tub boundary or under the adjacent wall and causes long-term rot issues.

Answered 2 years ago by LCD

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