Hi
Me again:woohoo:
I have read your post about the insulation of your room in the roof and replied accordingly.
I would suggest an easy way to prove heat loss in this case would be to show that the, supposedly insulated, roof space leaks air.
Manufacturers of gas flue blocks such as Dunbric can supply smoke pellets that are used to test the integrity of the chimneys built with these products.
If you were to (taking care to insulate the pellets from surrounding surfaces with a block or metal sheet) light a couple of these within your roof space you would be able to prove to your builder the extent of the air leakage in your roof by photographing the resulting smoke pouring from the soffit vents in the eaves. Warn the neighbours before you do this

hmy: