Dwarf walls in loft conversion

[Buildermonks]

I have had a loft conversion partially completed with dwarf walls fiited as required. However LABC have instructed me to support a section of the hipped roof with a dwarf wall resting on 9x2 joists which at present is unsupported and was left intentionally by the builders because it was never supported with any structure before (1930s bungalow) . Now if I were to construct a dwarf wall which is the same as the others this will cut down the size of what will be an already small bathroom, so I would like to keep the dwarf wall as low as possible to give me more floor/ cupboard space. Is there any regulations which state what percentage of the existing roof rafter should be supported (I would like the walls to be as far back into the eaves as possible)? I don't really want to get the inspector round again as he's a pain in the proverbial and always finds fault with anything he can find as it is! I am completing the loft myself and have built a few extensions before but never a loft so this is new territory for me.