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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: Suttonfire on September 14, 2015, 04:33:00 PM
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Hi All,
I note that the ADB states that a roof void above a fire resisting ceiling can be up to 30m (section 9.10c), whilst 20m is allowed in non fire resisting ceilings (table 13).
However, it also states in section 8.22 that compartment walls used to form a separated part of a building should run the full height of the building in a continuous vertical plane.
When applying this to a block of flats this seems to indicate that walls which compartment flats from each other and from the common areas should be extended into the roof void (up to the underside of the roof).
I have seen many roof voids accessed via common areas which are not vertically compartmented from the areas above the flats. Would you apply the 20/30m guidance in this case, or recommend that compartmentation is upgraded (very difficult I would assume - I understand that cavity barriers are not adequate as an 'extension' of compartment walls into a roof void). Or would your view be that if the roof void is well managed in a low risk building (secure, no storage etc, retrospective compartmentation would not be necessary).
I would appreciate any views on this.
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What you describe is commonplace, and the answer is any of the above depending on the circumstances. It is absolutely appropriate to point out such variations from good practice during a risk assessment, with full regard to the age and design strategy for the building, but is it reasonable to expect the action plan arising from such an assessment to incorporate often major and fundamental building works? No it is not.
We have do what we can to identify shortcomings and evaluate their consequences should a fire occur, and to mitigate such consequences as far as is reasonably practicable. If its there and broken - fix it. If its never been there in the first place then its a different matter and management of the risk may be the only way forward.
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Thanks,
Just for clarify, would you consider that a compliant current purpose built block would have all compartment walls from flats extended up through the roof void?
Or, is a void of up to 30m/non fire resisting void up to 20m OK as per current guidance?
My reading is that both options are set out in ADB. thanks
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The compartment walls should extend through the roof void.
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Thanks - So what would be considered to be a reasonable recommendation when coming across a (common) scenario in a typical block of flats in which the compartment walls within the flats have not been extended into the roof void? As Kurnal has alluded to it is not going to be practical in most cases to extend walls into roof voids. Would the installation of fire curtains or cavity barriers in line with the compartment walls be more practical? Or nothing at all provided that other fire risks are adequately managed (although its not possible to manage fire risks within a flat which may result in the open roof void being affected)?
I appreciate that ultimately the solution should be based upon the risk assessment findings but I would like to gather information on what would be considered reasonable similar situations.
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We must always take into account the age of the building and the design strategy. But yes cavity barriers and curtains may be a reasonably easy fix. The proportionate response will depend on many factors including for examples size, height, dead end corridors or two way travel, number of flats so interconnected, travel distance and layout of the flats, standard of the ceilings.
Have found this same problem in a number of recent care homes too.
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Which walls in the care home did not extend thro' the void Big Al.
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those subdividing the adjacent protected areas for PHE
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Was there no plasterboard ceiling?
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Diagram 33 ADB & 26 BS9991 shows the compartment wall going to the underside of the roof. To pick up on the earlier post - is it acceptable to use an alternative i.e double sheet the ceiling where the FFL is below 4.5m and incorporate the 20m cavity barrier in the roofspace?
I also have a sprinkler system within each apartment, the roof space is not accessible to the residents with a locked hatch within the communal area under the control of the factor for the common areas?
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i would suggest a sprinkler system is such a significant risk reduction measure that justifies variations in other areas - subject to risk assessment
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with a 10 minute water supply?
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I understand we are talking about existing buildings and in the original posting what could / should be done about the absence of compartmentation in the roof void. In such a scenario a the provision of a domestic sprinkler system offers very many benefits compared to the retrospective installation of fire curtains or cavity barriers without sprinklers - we have an active fire protection reducing risk at source, making a huge contribution to life safety within flats, providing protection to elements of structure, and will make its contribution wherever the fire occurs. To me its no contest.
For new builds I share your concerns over duration however in many of the scenarios frequently discussed as trade offs including within ADB. A summary of typical permissible trade offs for domestic sprinklers can be found here:
https://www2.redbridge.gov.uk/cms/planning_and_the_environment/building_control/who_are_building_control/idoc.ashx?docid=c8bbd55b-00ba-43a3-acf5-faaf5bac04b8&version=-1
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We are talking compartment walls here and not internal walls to the flats i.e. bedrooms and lounges etc that separate each flat from the other?
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Yes, the compartment walls between flats that on the top floor should extend through to the roof in order to support a stay put strategy. In this case, as in many thousands of other similar buildings, the flats on the top floor appear to share a common roof void. the OP was asking what, if anything needs to be done to reduce the risk to relevant persons. Now GB fire has asked about a similar scenario but where sprinklers are installed in each apartment.
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Diagram 33 ADB & 26 BS9991 shows the compartment wall going to the underside of the roof. To pick up on the earlier post - is it acceptable to use an alternative i.e double sheet the ceiling where the FFL is below 4.5m and incorporate the 20m cavity barrier in the roofspace?
I also have a sprinkler system within each apartment, the roof space is not accessible to the residents with a locked hatch within the communal area under the control of the factor for the common areas?
Not sure where the 'double sheeting' of the ceiling comes from, to be honest? Firstly two layers of ordinary plasterboard isn't going to give you an hour's F/R & in any case it only really works in risk terms if you have a F/R ceiling membrane (to the same rating as the compartment walls) in all the top storey accommodation (not just the corridor)?
Cavity barriers/curtains providing the same function as compartment walls are problematic because they're (generally speaking) not designed to be self-supporting, so strictly speaking the supporting structure ought to have the same F/R rating as the compartment wall - which will not necessarily be straightforward to design (especially for 'gang-nailed' trussed rafter roofs, which can collapse really quickly in a fire).
I know there's the 'reasonably practicable' test to be done where we're talking about risk assessing existing construction, but for new build or refurbishment the recommendations are hardly onerous...
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If the objective is to keep the fire from spreading beyond the compartment of origin, is it not a better solution to use sprinklers within the apartment to control the fire? What we are trying to do is allow the building to be constructed quicker with breaking up the roof space every 20m and not at each apartment boundary in the roof space.
The inclusion of sprinklers ought to be cost neutral for developers to incorporate them where there is no requirement for them. Is the increased safety within the apartment due to the sprinkler presence sufficient to remove the extended compartment wall in the sterile roof space?
How many times has fire broke into the roof space from an apartment fire when a sprinkler system is present within a domestic environment?
How many times has a fire spread along a roof space with compartmentation as ADB or BS9991 under the same conditions?
I am not sure that this statistical analysis exists - but it would sure be useful!
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the stay put strategy determines that the interior of each flat be fully enclosed within a 1 hour compartment such that in the event of a fire the fire is likely to burn itself out before it penetrates into adjoining dwellings. Generally passive measures such as compartment walls are considered more robust and reliable than active measures such as sprinklers which require regular maintenance. The responsible person is difficult to define - If each flat has its own self contained sprinkler system who is to ensure that relevant persons are not put at risk from a lack of maintenance? And if the system has only a 10 minute duration and it fails to extinguish the fire due to shielding or lack of maintenance then it might be considered that the solution ios inferior to the one hour compartmentation?
In this regard I ageee with Fishy- If this is a new build or refurbishment give the people on the top floor the same level of protection as those on the floors below. For an existing building fitted with sprinklers then I would consider the sprinklers a reasonable risk control measure and the FRA will provide evidence as to whether the systems are being maintained.
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What if fire occurs in the roof void!!!
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A Bit off topic but I suggest that the level of compartmentation may be questioned here ;)
https://www.facebook.com/pointswest/photos/a.886358191459325.1073742149.102814153147070/886358251459319/?type=3&theater
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I am getting this funny feeling of deja vu.
http://www.bbc.co.uk/news/uk-england-nottinghamshire-32117823
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Another one - seems to be quite a problem!
http://swns.com/news/14-year-old-destroyed-a-3million-block-of-flats-leaving-100-people-homeless-by-copying-a-school-science-lesson-and-building-a-home-made-bunsen-burner-68773/ (http://swns.com/news/14-year-old-destroyed-a-3million-block-of-flats-leaving-100-people-homeless-by-copying-a-school-science-lesson-and-building-a-home-made-bunsen-burner-68773/)
Question - it appears to be a deck approach to the flats above, presumably this would bring it into the RRFSO? (Not too sure if the stairs are at the ends.)
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I Wonder what the compartmentation in the roof was like in recent Bristol City student flats fire.
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Looking at the photos, to quote P Daniels 'not a lot'
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In reply to K Laird - the block in question did have comparatmentation between the upper maisonettes ( x12). Although the compatment walls did not pass through the roof tiles etc it was a solid block and brick wall up to the underside. The probelm in this fire, centres on the construction of the soffit and facia boards - which were made of UPVC and fitted with ventilation grilles ( as is required). The fire quickly got into the ventilated soffits and hence into the roof. Then due to wind conditions it flipped from one roof space to the next , to the next.
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I believe that the same happen here -
http://www.tamworthherald.co.uk/Blaze-hit-flats-months-fix/story-27552607-detail/story.html (http://www.tamworthherald.co.uk/Blaze-hit-flats-months-fix/story-27552607-detail/story.html)
Compartment doesn't pass through roof tiles, pretty common scenario.
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Just re-visiting this one as I have an upcoming meeting with a client who is responsible for blocks of flats at which fire resisting walls have not been extended into the roof void.
As we have acknowledged earlier in the thread that this is a common scenario, has anyone been involved with the implementation of risk reduction works in this respect? We have discussed the installation of fire curtains, cavity barrier and sprinklers earlier so I wondered whether anyone may have seen such measures implemented successfully? thanks
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Are there not cavity barriers in the roof void following the line of the flat compartment walls? Or is there no separation in the void at all?
Over boarding the existing ceilings to 60mins FR would be costly and disruptive to residents. The option of retro fitting barriers could be equally expensive and difficult due to access?
CT has mentioned what about if there is a fire in the roof void but what are the ignition risk there and also fire load?
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Just re-visiting this one as I have an upcoming meeting with a client who is responsible for blocks of flats at which fire resisting walls have not been extended into the roof void.
As we have acknowledged earlier in the thread that this is a common scenario, has anyone been involved with the implementation of risk reduction works in this respect? We have discussed the installation of fire curtains, cavity barrier and sprinklers earlier so I wondered whether anyone may have seen such measures implemented successfully? thanks
I have assumed that the existing ceilings are 30mins and not 60, if they are 60 then does the building not comply with the functional requirements of ADB, although not the diagram provided? i.e. 60mins FR between the flats?
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No. Fire gets into roof through the soffit then spreads sideways dropping into neighbouring flats.
If you really want an horizontal break then your ceiling needs to be FR when attacked from underneath and from above. Also, how exactly do you get the lighting to work without holes in the ceilings?
IMHO, an extra layer of plasterboard is not enough.
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To add clarity, In the cases I am looking at there is no vertical compartmentation within the roof voids. It is difficult to retrospectively ascertain the FR of the ceilings in all cases, but all appear to be a minimum of 30 minutes fire rated. From my understanding of the Building Regs and the responses on this thread the fire rating of the ceilings does not negate the requirement for vertical compartmentaion (or adequate compensatory measure) in line with the fire rated walls from the floor below.
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you get my vote
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Sorry, if I was confusing? Just to clarify then, 2 options as I see it:
1. No FR to flats ceilings but the flat walls (60mins) extended to true roof height, giving 60mins between flats and flats and common areas. This is as per the diagram in ADB and in an ideal world is the preferred option.
2. 30min or 60min FR to the ceilings but the flat walls do not extend to true roof height, but there are 30/60min cavity barriers (i.e. rock wool) in the roof void in line with the flat walls.
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Yes, but No 2 and the FR needs to go up and down - almost impossible to build - you have been warned.
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I have seen three solutions to this but retro installing a compartment barrier will always be a compromise and have several weaknesses in particular at the roof junction and at the head of the internal wall.
1- one local authority client installed plasterboard and stud partitions on the line of the internal walls within the roof void. They made a fair and durable job with access hatches using cut down fire door blanks, but this breached the fire door blank certification.expensive and messy.
2- a social housing provider installed rock wool FirePro mineral fibre cavity barriers again with cut down access hatches - fixing is critical at the head and base of the barrier, it is essential to follow the spec to the letter. The most appropriate and cost effective solution IMO if you are forced down this path.
3- another housing provider bodged it with smoke control curtain intended for subdividing cavities but ignoring the lack of integrity and insulation, the curtains were stapled together and within a year had been ripped asunder by other contractors. waste of time and money to achieve nothing.
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Wee B you are right as always but now that you can get B Regs approval from the world and his wife (in England and Wales, wherever the latter country is) you will find an A(dapatable) but Ignorant chap to approve it. Equally, in an existing purpose built block of not too high risk, you have to be realistic, and a cavity barrier would be reasonably practicable.
I like local authority building control-I always used to liken them to a squelch in 2-way radio (breaker breaker Big Al 10:4 will understand). It applied a bias current to that generated by the signal so filtering out the crap but letting good signals pass.
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Another solution might be to upgrade the ceiling to be a compartment floor, using the justification that if it was another flat above the then it would be acceptable for the flat accommodation to straddle the compartment wall.
BRE Digest 208 gives guidance using mineral fibre fixed with chicken wire between the joists and tongued and grooved floor boarding.
There could be an electrical fire within the construction and there could be a fire within the void, but these things could happen if it were a flat above.
You would need to check any penetrations, eg seal all holes and fit intumescent collars to the structure at soil pipe penetrations / pipes over 40mm dia.
The access hatch would need to be considered.
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Just remember that its the entire construction that gives you the fire resistance. Thats the ceiling, the joists (much bigger for floors that for ceilings) and the floor boards.
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Just remember that its the entire construction that gives you the fire resistance. Thats the ceiling, the joists (much bigger for floors that for ceilings) and the floor boards.
Ja - EI for ceilings, REI for floors (to BS EN 13501-2).
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Just remember that its the entire construction that gives you the fire resistance. Thats the ceiling, the joists (much bigger for floors that for ceilings) and the floor boards.
Ja - EI for ceilings, REI for floors (to BS EN 13501-2).
Ive amended my earlier comment as below:
"Another solution might be to upgrade the ceiling to be a [color=red]compartment[/color] floor"
The compartment floor would have stability (R) , integrity (E) and insulation (I). As wb pointed out above it is the whole floor that counts and exstg say "3 x 2", ceiling joists on their own wont suffice, new joists could be fixed alongside. The cavity above the mineral wool would need to be totally filled where it passes over compartment walls and around the perimeter. Trussed rafters would make it more complicated.
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Hi All,
I would appreciate some views re the legal requirement for any works in relation to this topic. We have established that compartment walls above flats should be extended into communal loft voids, and that were this is not the case various compensatory actions need to be considered.
I have a client who has asked 'is it a legal requirement to take any action in the communal roof voids as the property complied to the building regs at the time it was built?'
Can anyone give me some more detailed views on the legal status of these types of recommendations, which require retrospective building upgrades.
I would also be interested to learn whether it has ever been allowable under previous Building Regulations for compartment walls separating flats from eachother/the common areas not to be extended into the roof void.
Thanks
PS... Here is my take on the legal basis of the requirement to implement measures in the roof void, based on current guidance:
The law, The Regulatory Reform (Fire Safety) Order 2005 (RRFSO) sets general fire safety objectives to be achieved. For example it is a requirement of the RRFSO to ?reduce risk of the spread of fire on the premises?.
Accordingly, a Fire Officer could take enforcement action if he/she determines that by not installing compartments within the lofts the Landlord/Managing Agent has not taken reasonable steps to ?reduce risk of the spread of fire on the premises?.
Whilst the existing layout of the lofts may have considered to be adequate at the time of construction, it may not be considered to be adequate now (due to developments in technologies, and the understanding of how fires can affect buildings etc).
It is accepted that it is not realistic/risk proportionate to update existing buildings to meet all current approved guidance; however, the guidance should be used to establish just how far removed the original standards are from what is considered acceptable today, and whether this has given rise to an unacceptable level of risk.
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Just reading through this thread again, my scenario is slightly different in as much as the building is a supported living scheme so residents are more vulnerable. I have ruled out the over boarding option as it does not adequately deal with a roof fire or a fire spreading from a flat window through the soffit, the practicalities of carrying out the work and the additional weight applied to the structure.
My preferred option is controlling the fire loading and the installation of cavity barriers. But do I need to do all flats, every other flat or even every third flat? Could I extend the size with the addition of detection?
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I would always be inclined to provide, at the very least, cavity barriers at each compartment line if I couldn't provide full compartmentation.
I have seen this go wrong a few times, where the idea of a fire-resisting ceiling has been provided in lieu of vertical compartmentation.
Although it softens the blow, I do think that detection is inadequate mitigation in this scenario. Particularly as the likely intention is stay put.
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Just to pick this up again.
Would you consider that any form of retrospective cavity barrier is required if the floor within an open communal roof void is a concrete slab?
Obviously there is potential for fire spread across the open void but little chance of ingress into the flats.
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Can't envisage an issue with that and I'm sure the risk assessor would record the the matter accordingly after examining it. Problems tend to arise where the Fire Authority have been informed that the compartmentation will be taken up to rafter level at consultation stage.. and then find the premises has not been built to plan. But I can't imagine any objection being raised to this provided adequate fire stopping and intumescent materials are used where necessary.
There's a reluctance to accept horizontal protection in place of vertical fire barriers which is understandable. Systems are now available in which ceilings and floors can be upgraded to provide an hours FR from above and below and meet BS 476;pt 21 criteria. Whether the relevant stautory authorities will accept these or not seems to be on a case by case basis.
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Just to pick this up again.
Would you consider that any form of retrospective cavity barrier is required if the floor within an open communal roof void is a concrete slab?
Obviously there is potential for fire spread across the open void but little chance of ingress into the flats.
I would think cavity barriers would be needed as per ADB in this case. A similar scenario is discussed in the specialised housing guide, although different premises, the same principle would apply IMO.
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...Systems are now available in which ceilings and floors can be upgraded to provide an hours FR from above and below and meet BS 476;pt 21 criteria...
We'd be very interested in these (do tell who offers them)... British Gypsum used to do a variation of their 'MF' ceiling but they're reluctant to offer formal evidence of fire performance for it these days. I also thought you couldn't test a ceiling/floor from above to below under BS 476: Part 21 (only under the EN standards), but I'd be quite prepared to be proven wrong.
I wouldn't use it for resi, but we do have situations in non-domestic premises where corridor walls haven't been built up to the soffit (depressingly common) where it might be useful.
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You also need to consider the risk of a fire breaking out of a window, affecting the eves and getting into the roof that way. Also external fire on the roof due to hot works etc.