Surely if the extension was added in 1996 there must be some insulation in the flat roof? Can council not provide ANY documentation at all?
We have a 60's house that was built with a utility room at the back of the garage and door from kitchen leading into it.WC room in there too. Single brick construction.No source of heat. Freezing!
It had 70's mock wood cladding on the walls and T/G on the ceiling.Pulled all that off and there was about 50mm of some sort of soft plaster underneath.
People were quoting 6.5k to internally insulate the roof and walls, redo plumbing for loo,hand basin, pipes and fit rad' (boiler is in the garage) fit 3 base units, sink ,tap and worktop. Plastering. No idea what spec and no mention of buidling reg's approval, which is required.
Decided to DIO with reg's.
Walls -50mm PIR (between 75 x 50 battens with 25mm air gap as bricks only 110mm), 37.5mm insulated plasterboard over ( ideally would have been 67.5 ins'pb but we didn't have room behind doors/door reveals etc and the room is only about 2.4 mm x 3, so BR were happy with the 37.5, especially as we'd just had a new A* combi boiler fitted, several new windows and cavity wall to main house.
Ceiling 50mm between the roof joists and 67.5 insulated pb over
We haven't got any heat in there yet, but it's already considerably warmer, in fact probably warmer than the rest of the house without any heating on! New door into garage has helped too. If we put a little electric heater on on the frost setting it warms up really quickly and stays warm once the heater is turned off.
We're now thinking about either some IWI to the end wall of the house (hall /understairs/stairs part of landing) or as pointing on end of the house is poor, some EWI and cladding or render.