A recent case should serve as a reminder that rules are rules and 'close enough' often isn't!
The Town and Country Planning (General Permitted Development) (England) Order 2015 states that 'the enlargement, improvement or other alteration of a dwelling house' is a 'permitted development' (under class A), which subject to certain restrictions does not require planning permission.
So, when a garden room was built on a residential property, that should have been that. However, a visit by the building inspector uncovered a fatal flaw…the garden room was not physically connected to the house, there being a gap the width of a finger between the two.
This put the development outside the above rules and made it a 'class E' development ('the provision within the curtilage of the dwelling house of…any building or enclosure, swimming or other pool required for a purpose incidental to the enjoyment of the dwelling house as such, or the maintenance, improvement or other alteration of such a building or enclosure'), which is subject to different planning rules.
The result was that the extension was not permitted development. Enforcement action could therefore be taken unless retrospective planning permission is obtained.
Failing to comply with the letter of the law can have serious consequences.