I am of the opinion without any proof that this RO measurement has evolved a
bit over the years. Most likely as a result of the smaller tanks using 1.6
35 years ago if you were installing a new flange we measured out from the
studs 12-1/2". Then about 20 years ago that was suddenly leaving way too
much room behind the tank.
So let's surmise that it is now a 12" RO from the studs, add 1/2" of
drywall, 5/8" of base and 1/2" of shoe base and you depending on what you
measured, where and how well you could easily be 10-10-1/2" from the shoe
base to the center of the flange.
The only way you will ever know for sure is buy it, open carefully and dry
fit the thing.
I just went in and measure my Mansfield. The measurement is 11-1/2" from
the shoe base to bolts. The Mansfield unlike many cheaper BORG units has a
tapered back so that it is closer to wall at the top than it is at the
bottom. Even with that I have an inch between the tank lid and the wall.
Most of the BORG units have a straight back on the tank. Over the years I
have routinely added a small scrap of 2x4 to the wall behind the tank to
prevent tenants from breaking something when the feel the need to recline on
I have a hunch that the $80 jonnie in box from Lowes will work just fine for
you though you may choose to upgrade the seat.
Please come visit http://www.househomerepair.com
Here's a link to a few blurbs about the rough-in measurements, people's
As far as I can tell, different people have different preferences regarding
how far from the wall the tank should end up being. I have seen many setups
where the distance is one or two inches, and the two-inch distance seems a
little strange to me. I would rather see the distance be much smaller,
maybe 1/2-inch, but not have the tank actually touching the wall (so taking
the tank cover off won't involve rubbing it against the wall).
But, given the above discussion link, I think maybe you'll get what you want
by buying one of the 12-inch rough-in toilets you saw. If you take careful
measurements, which you appear to have done, the end result seems like it
would be that the 12-inch toilet you buy will fit well in the space you have
and will end up with the tank close to, or touching, the wall.
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