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Fire resistance of a ceiling


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Hi All

I wonder if you can assist.  

On the top floor in a care home the ceiling is 12.5mm plasterboard fixed to roof trusses not less than 38mm thick.  The plasterboard is skimmed and there is about 150mm of rockwool above.  This arrangement covers the top floor bedrooms, escape corridor and elec room, sluice room, clinic room and lounge etc.  The roof void above the protected area of 10 beds has cavity barriers and is free of storage.  The concern is the escape corridor and risk rooms may not give 30 mins fire resistance at ceiling level. The plasterboard is not fire rated and a fire ie in the elec room, or a bedroom could pass through the ceiling and spread in to what should be a protected corridor or neighbouring bedroom.  In the British Gypsum White Book such an arrangement with a 12.5mm fire line/board would give a 30 minute rating from the room/corridor side of the ceiling.  Does anyone know what fire rating single 12.5mm skimmed plasterboard offers? It may be that the fire breaking into the roof void and then spreading down in to a room within the protected area may take longer than 30 minutes.

Are there any documents which has the result of approved fire tests for such designs?? Basically i just want to ensure the existing arrange is safe or plan a cost effective solution.

Hope it all makes sense.  Thanks


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Hi Tom - thanks for your replies.  The thread has not had much activity so far.  I have looked at the information and links & the Rock wool flexi guide offers other ways for a 30 min ceiling/floor beyond the British Gypsum White Book.  On one of the threads a person mentions standard 12.5mm plasterboard single sided offering 15 to 20 minutes fire resistance - does anyone have any evidence of this???  I telephoned British Gypsum Technical helpline today but they can only offer solutions from the White Book.

Does anyone have any evidence of what a ceiling offers in terms of fire resistance made up of skimmed 12.5mm plasterboard fixed to 38mm roof trusses with 150mm rockwool infill between trusses.


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You could check out https://www.brebookshop.com/details.jsp?id=325239 (BRE digest 208) I cannot find any definitive guidance they all appear to point to nominal Fire resistance and not a full 30 min FR. Because you are looking to protect circulation areas you need full 30 min FR.

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  • 2 months later...

Hi Tom

The research established that there are a myriad of different plasterboards, thicknesses and manufacturers. For the FR on some it depends on roof truss spacing, nogging & nail spacing etc etc. Whilst the aim was to determine the rating of existing ceilings below roof voids without flooring above I didn't achieve that. On some you can see the boarding is pink and can google data printed on the boarding to further the research.

As part of my research I contacted various manufacturers who simply refer to there guidance docs/ data but you can't always ID who manufactured the boarding. Different manufacturers have different methods which go with their boarding to establish i.e. 30 min FR. I did not find anything published for single 12.5mm plasterboard FR rating with no flooring above. Other than ie fireline boarding.

i contacted companies which test normal plasterboard for fire ratings and was informed that manufacturers do have fire ratings for normal plasterboards. Whilst they are not 30 mins the info was not shared with me as their clients have paid for those tests. They were willing to conduct tests on any plasterboards for me at a cost.

Thanks to those who get involved with my initial enquiry.?

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  • 1 year later...

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