I recently bought this house with unfinished basement. It had a rough in for a basement washroom. I have 2 issue but the first is the toilet flang is approx 1.25" above the basement floor. I will be putting in tiles but this will still leave an inch. What is the maximum I could allow for, or could I cut the bottom of the flang and put a new one on as it looks like it needs it. I think if I cut it however the old flang will still be on the outside of the drain that was roughed in.

Looks like ABS pipe/flange... yes? If this is the case then can certainly cut flange off and install a new one. Could use an inside cutter to cut inside pipe just to below flange and then could chisel back concrete a bit and then hopefully prime/cement new flange over the pipe... but be clear chiseling concrete could break/crack the brittle ABS pipe.. but if careful will work fine.

Another alternative if you cut the pipe is to get an inside flange with a tapered rubber seal (sold at home supply stores) that is made exactly for this purpose... only drawback is that the outlet of flange is reduced compared to a full flange... but they work pretty good in a pinch.

Point here is you really don't have a choice but to redo flange... or build up floor (1/2" pressure treated plywood, 1/2" concrete board, 1/4"tile and thinset mortar should do it).

Hope this helped.. if it did please rate the answer below. Thank you.

Excellent help. I was thinking of raising floor with only concrete which would have been a pain to mix all for the entire washroom. I will also go look at the inside flange with a tapered rubber seal at the store to get an idea of what it is and how it would connect. I was planning on putting in electric floor heating so would have to find out if it will work with the wood and concrete board, but I don't see why not.

Thanks very much for you advice. Much appreciated.