NPPF Paragraph 84
NPPF Paragraph 84(d) treats limited extension, alteration, or replacement of existing dwellings as not inappropriate in the Green Belt, provided the new building is not materially larger than the one it replaces[NPPF]. Outside Green Belt the test is even looser; design quality, landscape impact, and policy-compliance carry the decision.
Materially larger test
Most authorities apply a 30-40% volumetric ceiling on replacement dwellings in the Green Belt; some specify GIA percentages instead. Read the relevant Local Plan policy before pre-app. Mole Valley, Waverley, Three Rivers and Buckinghamshire all publish per-district guidance.
Local Plan variations
Surrey districts and Bucks Council typically permit replacement dwellings on a generous plot where the new dwelling reads as one volume. Brentwood and Epping (Essex) and Three Rivers (Herts) are similar. Sevenoaks (Kent) takes a stricter design-led approach. North Yorkshire National Park authorities apply tighter materials and form controls.
Appeal outcomes
Planning Inspectorate appeal data shows replacement-dwelling refusals overturned at roughly 35-45% on written-representation route. The strongest grounds for appeal are: established case-law on materially-larger test, demonstrably superior design vs original, and proper biodiversity net gain submission.