The problem with the pre-2008 rules was that you had to be adept at working out volumes. Presumably the powers that be then felt it would be easier just keeping to simple overall dimensions.
(though personally I always believed the 3m rear extension limit to be too small. When allowing for the thickness of the wall, it doesn't give much extra space; 4m would have been more reasonable).
(though personally I always believed the 3m rear extension limit to be too small. When allowing for the thickness of the wall, it doesn't give much extra space; 4m would have been more reasonable).