Ok to cut my CI closet bend riser above the closet bend hub?

[Dougster]

This project started with a toilet flange wax gasket leak into the floor.

For my replacement floor I want to raise my toilet flange to the proper height, and bolt it to the floor. I also want to switch the current 4” cast iron flange to 4” PVC for future serviceability. (I prefer to avoid flange extenders. I've also read about removing the CI closet bend from the CI san tee hub and using a donut gasket but that seems overkill for my situation.)

My crawlspace has ~ 18” clearance to the undersides of my 4x6 girders. My 4” cast iron sanitary tee, closet bend, riser and hubs are 58 years old. Notably, the clearance distance from the top of my CI closet bend’s hub to the underside of my floor boards is about 6.5”.

It seems given this clearance it would be best to cut the CI closet bend riser about 2” above the hub. (To reduce the stress on the old hub joints underneath while cutting I would temporarily clamp the upper end of the CI riser to the floor boards or the adjacent 4x6 girder. I would prefer to use a soil pipe cutter since grinder sparks could ignite my blown cellulose debris.)

I would then use a no-hub to transition from the 2” CI stub to a Sch.40 PVC riser which is glued into a 4" hub PVC flange.

I would appreciate any tips or cautions and whether this is a sensible plan.

 

[Terry]

You can cut the vertical, but the horizontal may be an easier snap. It depends on which style cutter you are using.

 

[Sponsor]

 

[hj]

I would just remove the existing cast iron flange and install a new longer one.

 

[Reach4]

I would just remove the existing cast iron flange and install a new longer one.

Like this one maybe? https://www.plumbingsupply.com/toiletflanges.html#deep

 

[Dougster]

Re. PVC transition option (Terry):

• When cutting the vertical cast iron riser (above the hub), could a Sawzall give me the cleanest and safest cut?
• Based on my photos, will a wire brush and emory paper make the surface of the cast iron stub smooth enough for a banded rubber coupling?

Re. Cast iron flange change-out option (hj):

• What is the downside to simply packing lead wool onto the oakum? I don't have the pour kit or experience and it seems a little tricky pouring lead into a joint that is an inch below the flange. (Unless I can find an old-school plumber in my area.)

Re. InstaSet compression type cast iron flange option (Reach4):

• What is the downside to this option, e.g. what is the expected lifetime of the gasketed seal?

Thanks for your feedback!