I am remodeling a 1/2 bath and adjacent den in my 1940’s cape cod. The house sits on a slab foundation. The closet flange is brass/bronze with a lead riser. The flange neck is embedded in the slab floor. It is in excellent condition and extremely sturdy/rigid. In other words, i DO NOT want to remove the existing flange/riser.

Details….
I am debating two floor prep options that involve leveling compounds and/or schluter ditra decoupling membrane. My initial thought was to level the bath and den with a mono pour using Ardex K15. This leveling underlayment will have a buried electric radiant cable and increase the floor height by 1/2″. In the bath I would then use the ditra membrane to decouple the mosaic tile from the underlayment. I am estimating this will add another 1/2 to 3/4 inch to the overall increase in floor height. I am guessing that the top of the flange will between a 1/2″ and 3/4″ below the finished floor height. My second option was to install forms to prevent the leveling underlayment from setting in the bath. I would then set the radiant cable along with the ditra decoupler over the current concrete subfloor. This would greatly reduce the total add on height of the finished floor but will present other challanges not related to the toilet flange.  The finished floor in the 1/2 bath will be mosaic pebble stones.

I am seeking feed back on flange extension options, limitations to maximum height differential between flange and finished floor, wax build up, etc. Are there extensions made for this “antique” closet flange? Will a PVC extension kit work? Will option 1 create too much of a difference in height to correct? Are there other alternatives that allow me to replace the flange without breaking up the concrete and extending its height?

My preference is to go with option 1. Although, option 2 is doable I would like to avoid a transition in the door way to accomodate an elevation change between rooms and avoid the hassle of installing a pocket door frame kit at the edge of the newly leveled floor(don’t want the K15 to fracture in this area since it is close to the edge).

Also, my plumber will be finishing the relocated rough in next week. I will be floating these questions by him but opinions are like ********. I would prefer to have some proven techniques to bounce off him, he may not have knowledge of all of the options available for this situation.

Any advice is appreciated and I thank you in advance.