This is a cross section of the roof design.

For ventilation of the cold roof under the aluminium roof there is a continuous vented void running up the space between the T/F and exterior rendered cladding in to the roof space under the sarking.

Does this present a fire risk hazard? I understand there is a thermally reactive material which could be placed at eaves level which when warmed by fire will close off this area but obviously there is  a cost implication and how long will this be effective for?

The BR are OK about this I am just concerned that this presents a fire spreading risk to the structure.

Any thoughts?

It would be possible to separate the air flow from the rainscreen and the roof void.  Having fire resistant breather membrane on the timber frame would also help.  Once the walls are alight the roof would not be my main concern.  I have used the intumescent stuff between dwellings in a terrace but it is very expensive and probably not needed here.

yes there is a type of fire stop putty that expands when heated to do that job and block off  voids