How do I acheive a 'Fire Rated' Ceiling

[glangri2]

My 2 storey extension will have an integral garage on the ground floor, and 2 bedrooms above it.

Can anyone tell me how I can achieve the necessary fire rating for the ceiling, in material terms?

Strength wise, the wooden joists need to be 146mm min, but I have read on another post that for the fire rating they have to be 195mm min

Is this true?

If so, and I go for 195 joists with 100mm of celotex between then, fitted in the gaps and flush with the top ...............

What flooring to I need for te bedrooms ? 22mm ?
What thickness of plaster board do I need for the garage ceiling?

And if I go for fire rated low energy down lighters, can I run the cables in the 95mm gap between the top of the plasterboard and the bottom side of the insulation?

And do I need to use temp resistant cable?

Sorry for all the questions !

Cheers
Gary

 

[kevindgas]

the bits i can help you on

1. ceiling plasterboard use the foil covered type this has a 30? mins fire resistance
2. if you fit downlighters in it you will need a fire hood for each light

suggest you download building regs document B this has all the fire stuff in it

 

[glangri2]

I was having a look through the regs earlier, and couldn't find the info I needed in simple enough terms .................... mind you I was looking at it at work at lunchtime, so was in a bit of a hurry.

 

[freddiemercurystwin]

1 layer of 15mm fireboard beneath and 22mm t&g flooring (chipboard or plywood (preferably plywood with lots of screws to try and stop the creaking)) above will achieve 1/2 hours fire resistance. Technically speaking the joists should be at least 195mm high, the depth of the joists is derived from fire tests carried out by British Gypsum, Building Control may well accept lesser joists, you will have to ask them.

Or use 1 layer of British Gypsum 12.5mm SoundBloc board instead.

 

[tfish]

either red board or double board with 12.5 norm. you need to go crazy on insulation as well otherwise the cool zone of the garage will be drawn into the over rooms, a very common fault with inbuild garages