Compartmentation of roof voids above self contained flats

[Fishy]

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...

[GB]

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!

[kurnal]

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.

[colin todd]

What if fire occurs in the roof void!!!

[Bluffnpersuasion]

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

[Mike Buckley]

I am getting this funny feeling of deja vu.

http://www.bbc.co.uk/news/uk-england-nottinghamshire-32117823

[K Lard]

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/
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.)

[jayjay]

I Wonder what the compartmentation in the roof was like in recent Bristol City student flats fire.

[Mike Buckley]

Looking at the photos, to quote P Daniels 'not a lot'

[Argyle]

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.

[Dinnertime Dave]

I believe that the same happen here -

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.

[Suttonfire]

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

[William 29]

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?

[William 29]

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?

[wee brian]

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.