Replacement dwellings within the greenbelt are an allowable exception under national and local planning policy. National planning policy states that “the replacement of a building, provided the new building is in the same use and not materially larger than the one it replaces” is deemed to be acceptable

 

Every local planning authority have their own definition of what they consider “materially larger” when assessing greenbelt replacement dwellings. These definitions and policies range from around 5 – 35% of the existing dwelling or structures on the site. Neither national or local policies give a definitive definition of what “materially larger” actually is, however there have been many approvals and appeals which have to some degree given us a “rule of thumb” for what should be allowable.

 

There are 2 different calculations to look at when designing a planning strategy. The size of home extensions within the Greenbelt are based on the “original” house, as it was in 1948 (or when it was built if post 1948) while greenbelt replacement dwelling calculations are based on the “existing” built area on the site. Using these and clever interpretation of permitted development allowances we can often achieve permission for houses that are “materially larger”

 

More often than not, the brief we receive for a greenbelt replacement dwelling is to design a home that is as large as possible and WhiteBox Architecture has a great track record of designing and justifying homes that are “materially larger” than the one it replaces.