Lyledunn Posted June 26 Report Share Posted June 26 Three storey office building. This is looking up at the underside of the first floor. The ground floor is to be a day-time diner. The client wants to leave the slab exposed. I can get it repaired but would not be able to get confirmation of the necessary 60min fire resistance. Anyone dealt with this type of issue before? Quote Link to comment Share on other sites More sharing options...
AnthonyB Posted June 26 Report Share Posted June 26 How thick are the beams & boards? It would be very unusual for concrete used as a floor to be so insubstantial to be anything less than notionally 60 minutes. BR128 can give a pointer as to fire resistance if you know the thickness. Quote Link to comment Share on other sites More sharing options...
Lyledunn Posted June 26 Author Report Share Posted June 26 Thanks Anthony. The floor is circa 25years and was originally underpinned by a ceiling of unknown FR. Not sure about exact dimensions but blocks appear to be standard 220x110x440. Usual issue when BC asks for confirmation of 60min fire resistance. Perhaps obvious to all but no documentation to confirm. Reluctant to proceed with project without ticking that box! Quote Link to comment Share on other sites More sharing options...
Mike North Posted June 27 Report Share Posted June 27 You ned to know what is happening at the junction between the concrete and the steel beams, is there a path for fire and smoke to traverse the floor/celling. Is the steel frame protected? It looks like there are some major repairs to complete, and what is there concrete (is it RAAC) Quote Link to comment Share on other sites More sharing options...
AnthonyB Posted June 27 Report Share Posted June 27 In theory that thickness should achieve 60 minutes, but subject to the various caveats Mike mentions. You are unlikely to find anyone to certify it though so as daft as it is you might need to under draw the lot with a 60 minute White Book plasterboard solution Quote Link to comment Share on other sites More sharing options...
Lyledunn Posted July 1 Author Report Share Posted July 1 On 27/06/2024 at 07:23, Mike North said: You ned to know what is happening at the junction between the concrete and the steel beams, is there a path for fire and smoke to traverse the floor/celling. Is the steel frame protected? It looks like there are some major repairs to complete, and what is there concrete (is it RAAC) Mike, the beams are pre-stressed concrete with dense concrete block infill. Very common construction method and, amongst other advantages, particularly useful for giving a solid platform during construction in terms of safety. In the past there may have been a nod to the fire resistance of the arrangement, but no hard evidence in terms of certification. Things have changed dramatically in Building Control, certification is being demanded for just about everything structural. I have absolutely no dispute with that but it has often been a game-changer in our more recent fit-out contracts. We are in discussion with BC regarding the issue. Your point about the gaps between the blocks was raised. There is a 75mm sand and cement screed to the floor above so whilst the complete structure might achieve the R, the E and I are less obvious. In any event, we can’t get certification so it looks like we will have to underdraw a 60min ceiling as Anthony indicated. Quote Link to comment Share on other sites More sharing options...
Mike North Posted July 1 Report Share Posted July 1 Can't you claim the screed as protection Quote Link to comment Share on other sites More sharing options...
Lyledunn Posted July 6 Author Report Share Posted July 6 On 01/07/2024 at 15:24, Mike North said: Can't you claim the screed as protection Yes, I could, but I have no formal test documentation. It is being considered by BC at the moment but that can’t be the end of the story. Just because BC are satisfied doesn’t necessarily mean others will. I am aware of technical disputes between BC and Fire and Rescue Service on similar issues. Perhaps the insurance provider might also be concerned. I have issued instructions to ensure that the ceiling is repaired and all openings and penetrations properly sealed irrespective of whether we end up underdrawing the floor with a 60min ceiling. From an academic perspective, if we do drop a ceiling, any services installed above the ceiling will effectively be above the fire line and any apertures cut in the ceiling for lighting or ventilation will need stopping. That might sound silly, but if it is determined that the floor slab is not suitable, then we should really be installing a 60 min ceiling, then our services then another decorative ceiling. Eh!? Funny world, compliance! Quote Link to comment Share on other sites More sharing options...
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