What is the specified U value for roof insulation in a loft conversion?

if the ceiling is horizontal above your head (ie not sloping) it has to have a value of 0.16W/m2degC.

The sloping sections need to be a min of 0.2.

To give you some idea of how much insulation you need now, the horizontal area will need 250mm of mineral wool quilt. you need 1 layer of 100mm and 1 layer of 150mm - you need to put 1 layer running in between the ceiling joists and the other perpendicular running across the joists.

the sloping bit can be a bit fiddly - but if you want a bit of help I should be able to help you sort something out.

Cheers for the reply. Its actually for a friend so I'll pass it on to him.