Diagram 2.5 Ground or basement storey exit into an enclosed space

Where escape from a dwellinghouse is to an enclosed space with exit only possible through other buildings (e.g. a courtyard or back garden), the length of the space should exceed whichever is the greater of the following.
a. The height of the dwellinghouse above ground level (x).
b. Where a rear extension is provided, the height of the extension (y).
See para 2.10