Closet Flange level to finish floor but gap to sub floor

[boardryder]

Hi All! Hopefully I can describe this without a picture.

I have a closet flange that is level to the hardibacker board and 1/4" below the finish tile floor which should be fine to install with a possible extended wax ring. The problem comes in that there is actually a gap of 3/4-1" between the bottom of closet flange ring and the old plank subfloor. It's an old lead pipe and in tact flange with the hardibacker fit snug around the flange so not much rocking could happen and it would take a lot to move the pipe up and down. Will I be safe with the gap as long as I anchor the flange in place? Also, the subfloor where the anchors would screw in may not hold a screw, due to years of wear and replacements. Any input on that? Maybe something to fill the gap?

[Gary Swart]

I'd be concerned with the lead pipe. Any movement, rocking or up and down, will break the wax ring seal. As far as anchoring into the old plank subfloor, you could use plastic or lead sleeves into the planks then #12 stainless steel screws into them. I use lead sleeves into concrete anytime I need to attach or anchor anything and they will hold forever. Plastic would probably work OK as well. But, I'd sure deal with the lead pipe situation. Better to spend some time and perhaps $$ now while you're at it than regret it later when you have to rip up the flooring and redo the job.