Convert a Garage loft to a habitable box room

[Neoc]

Hello 

 

I have a planning permission for a garage and a porch conversion for my semi. Currently I have a pitched roof on my garage which will stay the same after conversion, and have a decent amount of space in the garage loft for a small room - circled in the picture below.

 

Do I need a planning permission and building regs for converting the garage loft into a small box room once the conversion concludes ? I have been told by my builder its not required as its internal but I want to be on the right side of the law. The stairs to this box room will be from the converted garage

Edited January 10 by Neoc
extra info

[joe90]

So what is your planning permission for? And why isn’t your box room part of that application?

[Neoc]

Planning permission was for garage conversion to a room and the porch. I have realised after the permission that there is an opportunity to put the loft also for use which is an afterthought 

[joe90]

I would guess your builder is right, even with a velux window but it might be worth changing your permission (others here will know more about that) and include a dormer on that roof to give more room. 

[Tomsbuild29]

Interestingly I'm in a very similar position. We've converted the garage to a toilet and office and now we've been toying with the idea of converting the loft. 

We have converted the garage under permitted development to regs with building control etc and my understanding is that we could do the same with the loft. Have you had any designs for the loft or are you holding fire?