Finished floor level below ground level

[Mark0395]

I’m converting a barn and have found the floor level at one end of the building will be lower than the floor of the building on the other side of the wall. The height difference will be 15-30cm. The rest of the walls will be well above ground level. However I can’t lower the floor in the building behind the barn. Will I need to tank out that wall or would extending the DPM up the wall 1m be enough. The yellow line is the problem area which is about 6m long.
Also the building behind has a concrete floor that slopes away from the conversion building.

 

[23vc]

Lapping the dpm up the wall should work if I’m reading the question right
Should go up to wherever the dpc is at that point rather than 1m up

 

[Mark0395]

Unfortunately no DPC as it’s a cobble stone building that’s about 200 years old. I should have mentioned that in the post.