I have a detached brick built garage set back 1m from the rear of my 1930 semi. It's got a flat concrete roof and no dpc. I am planning to convert it to an office/playroom. Planning don't seem to be interested and the local building control think it's exempt from building regs (class 6 exempt i.e. detached outbuilding less than 30m sq, brick built and not to be used for sleeping). So it sounds like I can do what I want internally.
My initial plan was to construct a inner block work room and fill the cavity with rockwool but I have just found the metal studwall/partition wall system at wickes. It looks very quick but I'm after some advice on the dpc and where to insulate the stud wall? And any general advice?
For the dpc I though of using a plastic sheet laid on top of the current concrete floor, all in one piece and then turned up at the walls about half a metre (will it be ok to leave the outerwall without any dpc??). I then thought of building the metal stud wall on top of the dpc. I can fix the top of the partition wall to the underside of the concrete roof but if I fix the bottom it will go through the dpc sheet! Any ideas?
The new floor would be 50mm polystyrene sheet with chipboard on top sat on the dpc plastic sheet. How does this all sound?