30m2 garage build.. inside floor measurement?

[leebleez]

Hi,
I'm currently looking at taking down my original garage and building a new one.
I'm intending on insulating the whole thing so I can work on my car through out the winter.
The garage is against my boundary but I'm hoping to maximise the floor space and will be made of brick (non-combustable) and insulate, making the internal walls 100-150mm thicker than just brick with insulation, battons etc.
So my question is does the 30m2 floor space rule, start from the internal finished wall floor area or from the footprint of the actual building.
I'm hoping to not have to go down the building regs route, so I will build it to suit but I get conflicting answers browsing Google.
Many thanks for your help
Cheers Lee

 

[Screech20]

30m2 finished internal floor area

 

[leebleez]

Thanks Screech for the reply,
It's looking like I will have to go down the building regs root due to the finished ceiling height being to low for a lanky guy like me.
Another question is. Assuming I want to just build to my max area giving floor area of 35m2, roof height of 3 metres and being on the boundary is it likely this will be covered with just building regs or would I need planning permission.

Cheers