Replace plywood under toilet

[icboet]

Just wondering how difficult it is to replace plywood from under the toilet. We are replacing the toilet but there has been a lot of water leakage downstairs. We can see through the basement ceiling that around the toilet looks black and white powderish...rotten I presume.

How difficult is it to replace just the plywood subfloor under the flange? Can anyone explain?

[SSN596]

I hope you are talking about taking up the finish floor and working that way. In this case, it is not a big job. You need to make cuts on the joist centerlines for support. Or just sister some 2X6 or 2X8 in at appropriate places. If the new finish floor will be sheet goods, you need to be quite fussy about nice joints, and even then I would plan on using some 1/4" luan sheet as an intermediate substrate. If you are going with ceramic, you need cement backer board.