I have to replace the floor under the toilet because it was rotten.
The toilet flange is cast iron (the house is over 60 years old); it is still in excellent shape.

I prefer not to remove the flange from the cast iron pipe (I am an amateur, and don’t like to mess around with these ancient hardware). If I made the new flooring under the toilet from two pieces (to go around the flange), and connect the two with a 1/4” thick steel plate (from underneath), do you think the floor will be sturdy enough to prevent an wobbly toilet.
(There is not enough room under the 45 degree drop kick cast iron flange for a thick ply wood / lumber).

Do you have any other suggestions? Is removing the flange from the cast iron pipe easy enough to be done by an amateur? Many thanks,
nodelac

I may be misunderstanding you but your should be putting down at least a 5/8 or 3/4 plywood flooring. Are you saying that you can not slide a piece of 5/8 plywood in unedr one side of the toilet flange?

Many thanks to ballengerb1 for your quick response.
I will be using a 1" thick plywood, and will be able to slide underneath the toilet flange, however I will have to cut the plywood in 2 sections (of which each will have a half hole of approximately 4.5" diameter, because the flange outside diameter is 7" and the cast iron piping is 4.25" O.D. (the flange is still attached to the cast iron piping; and I don't like mess it up by trying to detach it from the cast iron piping).
Cheers,
nodelac

OK I better understand you. I would suggest cutting a large U shaped slot in the plywood and then slide the U under the toilet. A U slot gives support 3/4 of the way around the toilet rather than two half circles. The bottom circumfurence of the U slot should be 4.25" and the falne top surface should be just above your finished floor surface. Will you be putting down ceramic or vinyl or what?

Thanks for your quick response.
I will be installing ceramic tile. At the moment the old flange is sitting on the new 1" wooden floor. So I think I will have to buy toilet flange extension kit tom raise the flage to above the ceramic tile. Is taht right?
Eventually two sheets with half 4.5" diameter holes, and managed to add additional support to the new floor from underneath. It seems to be quite sturdy.
Thanks for your input.

Your flange can be flush with the floor surface or it can sit on top of the floor surface. Nything within this tolerance will be OK with a standard single wax ring.

Mmm

ICEBIRD, interesting comment!

Install 2 halves of ply. Put 2x4 at the cut. Secure with lots of 1 1/4" coarse drywall screws.

Since you have to build up the replacement floor 1', I suggest you make one piece out of 1/2' ply riped down the center of the hole like you stated. Then make the second piece but rip it through the center of the hole the opposite direction. When screwed together one piece will support the other.