Hearth construction and dpc

[Tonythecat]

Hi all I'm new to this forum and hoping someone may be able to help/advise
So I am in the process of preparing my hearth and fire place for a stove. I have everything out to the original builders opening and the hearth down to about 200mm below floor level (floor is suspended t+g boards on joists) the hearth is constructed on a brick fender type construction with rubble infill which extends down approx 2m under the floor to ground. A bitumin doc runs around the brick fender and joists are built into it
The joists have perished and need replacement
I plan to build the fender level back up to floor level and install new hearth on top. But new joists will be supported on hangers attached to the fender. Instead of being built in. My question is around installing a dpc into the fender. Obviously as I have down by 200mm I can add a membrane before I build back up but the membrane will be lower than the dpc which runs in the walls. And I cannot turn it up the wall as it will bring it too close to the stove. Is it just acceptable to lay it in and build up on top
Cheers

 

[Tonythecat]

I've added this drawing to help to explain. The red line shows where the dpc was fitted and the joists extended into the fender and sat on the dpc. Ive shown the level that I'm currently at and how the joists will be supported when I build it back up