I have a house that was built in 1870, and the upstairs bath floor is very
soft and creaky (I'm 180 lbs and I worry about my foot going through it one
of these days). It is a very small bathroom, with the worst part of the
floor between the toilet and shower (about 2' square). I want to pull out
the toilet and the carpet, and replace the subfloor. (for what it is worth,
the damage likely came from an earlier toilet leak, or the fact that someone
put the bath vent into a wall cavity and I'm sure it just condensed the
moisture and ran it right down to the floor).

I pulled back the carpet to see what was under there, and right in the
middle of my target area, there is a large round metal disk (5" diameter)
with a bolt running downward (bolt head is hex, 1 1/4" diameter). I've seen
similar things used for structural support in old brick buildings (like in
New Orleans), where the bolt holds two plates together, one on either side
of the building. In my case, however, the bolt goes straight down.

As far as I can tell, the bolt is above my dining room, so it doesn't go
very far, because there is no sign of it on the dining room roof.

So I have two questions, before proceeding:

(1) What precautions should I take when removing the subfloor- should I try
to leave the bolt where it is? I don't think I can really replace any part
of the floor without removing the bolt, so if I have to leave it, I'm
hosed..

(2) were these types of support plates used for anything other than
structural support? for example, the drain line from the toilet probably
feeds under this area toward the main drain which is next to the shower. Is
it possible that someone used this to support the toilet drain? If so, what
should I do? If there is a cast iron pipe under the toilet, I'd rather keep
it (to keep the noise down, PVC drains are just too noisy), but I'm not sure
if I'll just get stuck putting a big bolt back in the floor to hold it,
ruining my chance to put down a tile floor.

Any suggestions, and your voice of experience, would be greatly appreciated.


Thanks,
Keith