Proposal 3 - VM2 Vertical spread of fire scenario (VS) changes

Proposal 3 - VM2 Vertical spread of fire scenario (VS) changes

The full details of the proposed changes can be found here

You should also respond individually to the MBIE questions which can also be found at the above link.

In light of the Grenfell Tower fire I would hope that MBIE consider banning the use of all combustible cladding

No more timber weatherboards on houses or schools?

I think the issue here is the extent of the changes, and reasoning behind them. I’m currently working on a sprinkler protected, two level office (330 m2 per floor) (8 m in height), where the client wishes to have timber cladding on one elevation. The reasoning in the Codewords issued stated the dispensation for sprinklers was being removed to protect means of escape and fire fighting operations. I cannot see how timber cladding on a two level small sprinkler protected building can be that detrimental to means of escape or fire fighting operations. I do agree with increasing the requirements for ‘tall buildings’.

Maybe 2 floor levels rather than 7m would be a better way of controlling it.

Two or three levels would be reasonable. Perhaps 3 levels as a limit? Why restrict someone’s choice in materials for their 3 storey house?

3 storey house would come under C/AS1 and has a 10m limit.

That said what would we be achieving by restricting timber weather boards to active occupancies such as schools and offices of a similar height?

At IFireSS a few weeks ago there was an interesting paper about testing of external foamed insulation… Of interest is the effect of relatively minor damage of the coatings (>25* peak HRR ) and the doubling of peak HRR when a different installer was used. I can’t seem to uplaod a pdf here, so email me if you want a copy

Agreed, hard to see the risk for the timber weatherboard case.

The 7m limit has been in the acceptable solutions for a long time however the original definition of building height was similar to escape height so 7m meant a three storey building would have been ok instead of now only a single and maybe a 2 storey building. Probably the height limit should have been adjusted at the same time the definition was adjusted.

C/VM2 currently would allows schools and offices under 10m in height to be exempt from the VS scenario so timner cladding would comply.

In the VM2 proposal table 4.2, why are buildings under one ownership and no sleeping (office buildings for example) able to go to 60m able to have combustible cladding or weather boards? While there is no other property/ sleeping in an office building, the Grenfell tower and others showed how rapidly such cladding fires grow, the issues involved in escape as a result, and the impossibility of fighting the fire externally that is outside the 25m or so reach of the aerial appliance. A limitation (at least B rating) should apply 25m+ to all buildings. I do note that table 4.1 (horizontal fire spread) has B type limits at 7m+. It should be cross referenced and consistent - and what about that tall-ish building in a large estate under one ownership, so there is no other property for miles away?