15sqm Permissible Dev, interior floor space?

[Mike_M]

I think i read it right, but can anyone confirm the 15sqm permissible development is on INTERNAL floor space, not the exterior size?

[Conor]

Gross floor area, so internal floor area, inclusive of voids and walls.

[Temp]

And as far as building control are concerned you can go upto 30sqm under certain conditions...

 

If the floor area of the building is between 15 square metres and 30 square metres, you will not normally be required to apply for building regulations approval providing that the building contains NO sleeping accommodation and is either at least one metre from any boundary or it is constructed substantially of non-combustible materials.

[Mike_M]

thanks guys.  I'm with a metre so will keep the plan as is, 15sqm including of walls

[DevilDamo]

Permissible development but I’m sure you mean Permitted Development? PD being Planning of which they’re interested in the external footprint while Building Regulations are interested in the internal footprint.