Garages with area greater than 40m2!

[Radian]

Regarding Approved Document B (Fire regulations) I've been puzzling over the "purpose group" into which our existing detached brick & block garage/workshop falls. Our current project involves an extension to to the side of the workshop providing an new additional ground floor room containing a staircase to the entire roofspace above (formed out of new "attic trusses"). I had expected to have to line the underside of the garage roof trusses with double layer of plasterboard to give the usual 30 minute fire resistance - as is required for a house with integral garage - which has a concrete block cavity wall extending to the roof ridge.

 

However, our garage is 6m x 7m which is 5% bigger than the 40m2 maximum for it to be included in purpose group 1(c) (as per table 0.1). Given this, it appears to default into Group 7(a) "• any building not within purpose groups 1 to 6."

 

This has an enormous effect on the fire requirements -- 90 minute resistance not 30 for example and puts all kinds of additional demands that weren't anticipated. My head is still spinning trying to follow the relevant details in the regs. that mostly seem wholly inappropriate to our situation. No it's not commercial or open to the public nor has it 150 occupants!

 

Surely the intention of purpose group 1(c) was to cater for a typical 2-car garage? 7m isn't even quite enough width to comfortably get in and out of two modern parked cars. This must have bitten other people so I'm wondering if there are any known workarounds?

[PeterW]

Can you not use an external staircase ..?

[stephen margerison]

Have you spoken to your building inspector ? they can be very helpful

[Radian]

Hi PeterW, well, the stairs aren't the problem (I hope!) They're already in.

[Radian]

Hi stephen, that's our very next move only this all kicked-off after close of play on Friday (as always seems to happen) Been stewing on it all weekend and decided to cast around here for ideas.

Is it possible BC may make an exception? I mean, is there an element of discretion available or are "rules rules". Never been in this kind of situation before.

[Oz07]

Be a shame if your drawings showed it one block shorter than you built it! 450mm on the long side gets you below with my reckoning

[Ian]

9 minutes ago, Radian said:

 

Is it possible BC may make an exception? I mean, is there an element of discretion available or are "rules rules". Never been in this kind of situation before.

It depends where you are building in the UK. In my experience there’s a great deal more flexibility shown by BC Inspectors in England & Wales than there is in Scotland.

[Radian]

How many people must there be with double garages exceeding 40m2? 6m seems a fairly common depth - so width greater than 6.66m would put you in "no man's land" group 7(a). Opening both sides of a 2m wide SUV in less than 3.33m is not all that practical. I bet the 40m2 figure hasn't been updated in over 40 years.