I have just finished rebuilding my camp. My contractor had to raise the height of the foundation about 4 inches to allow for drainage. The existing toilet waste pipe is cast iron and is now 3-4 inches below my sub floor. I only have about 8 inches clearance between the granite that the camp sits on and the sub floor. I haven’t been able to find a PVC flange that has a long enough pipe to extend down to the waste pipe. Do they make such a thing as a waste pipe extender? The cast iron pipe extends about 3-4 inches high above an elbow that sits at/slightly below ground level with piping that is slanted under ground to the septic. I don’t have much pipe to work with (meaning if I screwup cracking it off I could be screwed) and I have next to no room to work in. Can the flange be extended by adding 3 or 4 inches via a pvc coupler? Worried about "structural" integrity. One other thing to note – camp is in northern NY so in the winter it gets pretty cold. My solution has to stand up to mother nature. Any thoughts would be appreciated.

I don't know of a PVC fitting that would fit in the 3-4 inch space that you mentioned but they do make a PVC pipe that has a coupling built onto the end of the pipe. It is swaged on the end and when slipped over a 3 inch PVC pipe it only takes up about 1 to 1-1/2 inches, that would leave you 1-1/2 to 2-1/2 inches for you flange to glue onto. Now at to find out where you might find one of these pipes without having to buy a 20 foot section I am not sure but I do know that people that install irrigation systems use them, they might possibly have one laying around.

Use a shielded clamp to connect from cast iron to pvc. Then you should only need a short piece of pvc to fit into clamp