If you’re planning to create a room in your roof, you’ll need to comply with Building Regulations which continually upgrade insulation requirements. You’ll achieve a much better (and almost certainly less expensive) result when you use Foamseal.
Foamseal, applied directly to the underside of the roof, gives an insulation value equal to twice that of fibreglass without the need of a ventilated air gap. It turns the whole roof into a ‘warm deck construction’ allowing draught and dust-free storage areas to be created at the eaves. Foamseal is sprayed snugly between the rafters so you do not usually lose any ceiling height.
The rafters can then be covered with plasterboard or plaster applied directly to the Foamseal to leave the rafters exposed.The room will be warmer in winter, cooler in summer and less airborne sound will penetrate your home.