Compartmentation of roof voids above self contained flats

[Suttonfire]

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.

[kurnal]

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.

[Suttonfire]

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

[colin todd]

The compartment walls should extend through the roof void.

[Suttonfire]

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.

[kurnal]

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.

[colin todd]

Which walls in the care home did not extend thro' the void Big Al.

[kurnal]

those subdividing the adjacent protected areas for PHE

[colin todd]

Was there no plasterboard ceiling?

[GB]

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?

[kurnal]

i would suggest a sprinkler system is such a significant risk reduction measure that justifies variations in other areas - subject to risk assessment

[wee brian]

with a 10 minute water supply?

[kurnal]

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

[William 29]

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?

[kurnal]

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.