These descriptions help compare designs, but planning rules assess the actual relationship to the original walls, not the marketing name given to the project. [1]
Rear extension
Use a rear option to test whether extending the existing kitchen or living space is enough. Include the old and new rooms on the same furnished plan, with the structural opening shown. This makes the comparison about the whole layout rather than just the depth of the addition.
A single-storey rear extension may qualify for ordinary permitted development or the larger-home-extension prior-approval route. All relevant conditions must be met; being within a headline depth limit is not sufficient by itself. [2] [3]
Side-return extension
A side return is the space beside a projecting rear part of the house. Infilling it can change the width and arrangement of the rear rooms without necessarily extending as far into the garden. Check the exact original footprint: stepped rear walls and the side wall of an original wing can each create a relevant measurement line. [1]
For the options exercise, ask how the original middle room will obtain light, how the roof meets the existing wall and whether access to the rear will remain. Historic England advises considering the significance of rear wings and the balance between the house and its yard, particularly in historic terraces. [4]
Wraparound extension
A wraparound joins the side and rear elements into one enlargement. It should not be assessed as two unrelated allowances. Both side and rear permitted development tests apply where the relevant walls are crossed, and the width of the combined enlargement can rule out that route. Building the elements at different times does not automatically avoid that assessment. [1]
Compare the wraparound with a smaller rear-only alternative. Identify exactly which extra activities the additional side space accommodates before asking builders to price it.
Two-storey extension
A two-storey scheme should be designed on both levels from the outset. Ask for the upstairs circulation, windows and roof junctions to be resolved alongside the ground-floor layout. The structural assessment must account for the loads from the whole addition and the existing building. [5]
Permitted development for an extension of more than one storey has substantially different restrictions from a single-storey rear addition. Among them are a 3m rear projection limit and the requirement not to be within 7m of an opposite rear boundary; side extensions of more than one storey do not qualify under Class A. [1]
Make the decision on a common brief
Compare each option against the same accommodation brief, drawing information and specification. Keep planning advice, structural feasibility and a costed schedule together. An apparently cheaper sketch is not a meaningful comparison where it excludes the opening-up work, drainage or finishes included in another option. [6] [7]