I have a converted loft which is really cold. The roof doesn't have any insulation, just a waterproof sheet, but i don't want to spend too much insulating it with the proper boards. If i use mineral wool and staple it across the roof trusses will it do a good job?
Yes, be sure to leave an air space between the top of the insulation and the roof deck to allow for ventilation, and use a vapor barrier on the interior side of the insulation.
