We are based in the north east of England and recently obtained planning permission, which included raising the ridge line of our roof. Our builder has now suggested that given we now have a good sized roofspace, we should consider doing a loft extension at the same time as the other works.
Our house is set in the middle of a large plot, is not overlooked and is not visible from the road. I understand that generally planning permission is not required for dormer windows that do not front a highway, up to a limit of 50 cubic metres for a detached house.
My question is whether this 50 square metres is calculated from the new roofspace, after it has been raised, or if we have to reduce it to reflect the fact we have already had planning permission to raise the roof?