A complex-shaped cut-out is
made in the sub-floor, a piece of treated lumber installed
for a spacer, and the offset flange is glued to the 3" drain
The previous owner had installed a cheap conventional plastic
toilet flange and had hacked out a huge notch in the side of the 2x8
floor joist to accommodate the plumbing. Our room improvements
included adding a layer of 3/4" foam insulation, followed by ½"
drywall. In the old installation the toilet was tight against the
wall. We added at least ½" to the wall thickness (the old
plaster-and-lath was about ¾" thick), so we knew that a conventional
toilet flange would only amplify the damage to the floor structure.
The PVC drain plumbing was installed a month earlier, and the
toilet flanges had been put in place but not glued (as is common
practice) until the finish flooring installation was complete. The
toilet flange can rest on the finished floor. The toilet horn, which
fits into the flange, is recessed into the toilet body and lies
about 1 inch above the floor level
||The 3" drain pipe lies just below the floor
level. We had covered the pipe opening with duct tape to prevent
tile mortar from getting on the pipe end (and to keep sewer
gases from entering the house during remodeling).
|The offset flange. Note how the pipe is not
centered directly underneath the red mounting ring. This is the
only sensible choice when a toilet must be mounted directly over
a floor joist.
||During tile installation we had left this
unusual shaped opening in the finish floor. We arrived at this
shape by test-fitting the flange and drawing lines around the
red mounting ring.
We made the complicated angle cuts (instead of making a
simple square cut-out) because it appeared that the back
corners of a square cut-out might not be covered by the
|We cut a 3/4" thick piece of treated lumber (1x8
stock, actually) to fit in the tile cut-out. Then we used a
4-1/2" hole saw to cut the opening.
||We tested the fit of the wood filler block. It
took several tries to get the shape just right, because of the
complex shape of the offset flange.
In fact, we determined from the test fittings that the only way
to attach the flange to the pipe was to slip the wood filler block
over the flange's pipe fitting and then slip the fitting on
to the pipe. There was no way we could install the filler first and
then connect the flange.
|We applied purple PVC primer to the pipe and the
fitting. We also raised the drain pipe up and secured it with a
temporary support, making sure that the pipe had a suitable
slope (1/8" to 1/4" per foot) when the whole job was done.
||We applied PVC cement to the fittings and stuck
them together. At this point the entire flange is elevated from
the floor by the temporary support.
|We re-positioned the pipe support and drove long
deck screws into the flange. Some of the holes at the back could
not be used because the screws would penetrate the pipe.
||We filled the gaps with caulking. It is very
likely that the wax toilet seal will leak someday, and this
caulking may prevent water damage to the wood floor structure.
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- Cordless Drill/Driver
- Heavy Duty ½" Drill
- 4-1/2" Hole Saw
- Offset Toilet Flange
- PVC Cement, Primer
- Deck Screws