Rear Extension - Proximity to Existing Outbuilding?

[subzero]

Detached property with detached garage/workshop, which is positioned such that the left hand side of the garage is directly in line with the right external wall of the house, and positioned about 3-4m behind the rear external wall of the house. See the sketch below.

This would make it seem impossible to add a full-width extension to the rear, so I have drawn up the following sketch for a 'gable end' style extension which would be not the full width, but would allow space between the proposed extension and the existing outbuilding. The question is, would this be allowable under PD?

 

[tony1851]

As long as the ridge height is no more than 4m, that would be permitted development.

There is no stipulation on the minimum gap between the structures; IIRC, there was an appeal case in which
a distance of 1" was sufficient to establish separation.