Cavity Barriers/Fire Stopping in Single Storey Detached Dwelling

[Martin81]

Hello Everybody,

I came across this very knowledgeable forum whilst trying to find an answer to this question, I do apologise if it has already been answered elsewhere:

To what degree will a single storey, detached timber frame chalet I will be building (a self-build project) require a) cavity barriers, and b) fire stopping measures?

The wall construction will be timber stud with voids totally filled with Warmcel insulation or similar. There will be a 38mm ventilation cavity between the outer sheathing boards/breather membrane and the timber cladding, but this is required to dry the walls after periods of driving rain. There will also be a 45mm service cavity on the inside between the vapour barrier and the 12.5mm plasterboard inner lining.

The roof construction will be timber rafters with voids totally filled with Warmcel insulation or similar. The roof will have a 55mm ventilation cavity between the sheathing/breather membrane and the metal roofing sheets, and a 38mm service cavity between the vapour barrier and in the 12.5mm plasterboard inner lining. The plasterboard will follow the line of the rafters and there will be no loft space.

This build is in Wales and so will have a fire suppression system installed (likely to be watermist) and all rooms will have an exit door or window to outside and a place of safety so there will be no protected escape routes. There will be no garage attached and the total floor area will be 63m2.

I believe I am correct in saying that the chalet will not require compartment walls. The plasterboard will be mounted onto 38 or 45mm timber battens, which I believe could act as a barrier in the service cavity if necessary as they also run horizontally along the top and bottom of the walls, around openings etc?

The Building Regulations don't seem to mention small, single storey structures in this respect and assume that all buildings will have at least two storeys and cavity walls (which I suppose many do, to be fair). I don't know if the same rules will apply here or if they are geared more towards safety and escape from larger/semi detached houses etc.

The way I read the regulations is that cavity barriers and fire stopping are required at joints between fire separating elements, and if I don't have compartment walls, do I need them, and if so, to what extent? If I have any of this wrong then please correct me, I am eager to learn.

I'm sorry this is such a long post, but I thought it best to give as much information as possible now to help build a picture of the proposed build. I may be able to post CAD drawings if it would make it any clearer!

Thank you in advance.

Martin

[Tom Sutton]

Your plans will be subject to Building Regulation approval so you will need to submit them to your local building control and they will correct any omissions. But my very basic knowledge would say you will have to install fire breaks, around any openings like doors and windows. Also if any internal walls needed to achieve 30 minutes fire resistance ( internal garage or maybe kitchen), they will need to be fire stopped and you may need to create a fire break between the walls and the roof. Study in fine detail ADB vol 1 B3, B4 where you will find out most about fire breaks.

Check and study Approved Document B (fire safety) volume 1: Dwellinghouses

[Martin81]

Hi Tom,

Thanks for getting back to me. I guess that Building Control will be my next port of call then! Thanks for your help.

Kind Regards

Martin