Going over 40m3 L Shape Loft Conversion issue? And eaves question.

[markymarky]

I'm having an L shape dormer built on a terrace house and the outer dimensions have gone to approx 41.7m3 and I'm worried it could cause a PD issue and will need to be taken down?!

Does anyone know if the 40 cubic meters is based on an internal volume measurement, i.e internal walls to walls, internal ceilings to ceilings; or an external measurement of the outer dimensions of the dormers?

The guidelines for the 40m3 rule seem to be a bit ambiguous and open to interpretation?

PD Guidelines state:
For the purposes of Class B “resulting roof space” means the roof space as enlarged, taking into account any enlargement to the original roof space, whether permitted by this Class or not.

To be permitted development any additional roof space created must not increase the volume of the original roof space of the house by more than 40 cubic metres for terraced houses and 50 cubic metres for semi-detached and detached houses. Any previous enlargement to the original roof space in any part of the house must be included in this volume allowance. ‘Terrace house’ has the meaning set out in the ‘General Issues’ section of this document (see page 6).

‘Original roof space’ will be that roof space in the ‘original building’ (see ‘General Issues’ on page 6 for the definition of this).

(d) the cubic content of the resulting roof space would exceed the cubic content of the original roof space by more than -

1. (i) 40 cubic metres in the case of a terrace house, or
2. (ii) 50 cubic metres in any other case

Is ' roof space 'deemed an internal measurement or external measurement? And above uses the word cubic 'content' which I believe means inside?

Lastly, can anyone also clarify; I know all eaves need to be reinstated at the back at least 200mm. But what about on the left and right side of the dormer where the party walls/chimneys are? I'd call it the roof verges if that makes sense? Does each side need be set in 200mm as well? Or can it go width to width of the internal party walls?

Thanks in advance

 

[Nakajo]

I don't think there's any case law confirming the position, but as discussed elsewhere on this forum, logic dictates that the calculation must include the external fabric, otherwise you could just stud out the internal volume until you were back below the limit. That said, how wide, and how deep is your terrace house? Because to increase the roof volume by more than 40m3 on a typical terrace house is quite an achievement.