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I'm having thermal and acoustic insulation fitted between the basement/garage and the floor above. There will be two layers of Knauf 90mm Earthwool Frametherm friction fitted between the floor joists (with a 500g Polythene vapour membrane). The Earthwool is a Class 1 fire rated product.

There needs to be a fire resistant barrier between the garage and living room above. I had initially planned to use a cheaper insulation product with less fire resistance, then fireboard + skim below the joists. However the insulation fitters have given me a free upgrade.

So...now I'm having a Class 1 fire rated insulation product fitted, do I still need to use fireboard, or can I use a cheaper board? NB: I only want one layer of board due to the small gap between the ceiling and top of the garage door.

I will run this past building control too, but I find it works better if I give them my thoughts for them to comment on, rather than ask them to specify whats needed.

Class 1 is a low rating, but normally 2 layers of fire rated plasterboard is ok in a garage to give at least 1 hour.

Single layer 12.5mm Gyproc WallBoard each side of Gypframe 48 S 50 studs provides 30 minutes
Single layer 15mm Gyproc FireLine each side of Gypframe 48 S 50 studs provides 60 minutes
Double layer 15mm Gyproc WallBoard each side of Gypframe 48 S 50 studs provides 90 minutes
Double layer 12.5mm Gyproc FireLine each side of Gypframe 48 S 50 studs provides 120 minutes

Thanks. So the increased fire rating of the insulation has not resulted in being able to downgrade the type of plasterboard I need to use for the ceiling.

Building control are coming today so I'll stick to my original plan of a single layer of Fireline.

Coming back to this again, I'm confused by the reference to Gypframe studs. If I'm attaching the board to wooden ceiling joists, can they be screwed on? What are the studs for?