W e have built an extension to our house, which includes a garage with a bedroom above. We have lined the walls and ceiling with two overlapping layers of 12.5mm plasterboard. Are we required to have a plaster skim applied over the plasterboards, in oder to obtail Building Regulations final approval?

(Please note, we have already had the relevant electrical work certified by the qualified electrician, who installed it.)

Check out Approved document B (Fire Safety) Vol 1 my understanding is it requires 30mins FR between an attached garage and the house. Two overlapping layers of 12.5mm plasterboard skimmed will give you 60mins, one layer skimmed would give you 30mins. I would suggest you contact your building control officer as you appear to be between two stools.

Check out http://fire.org.uk/forum/index.php?topic=5055.0 for more info.