You can extend a house in Petts Wood, but it involves more paperwork than the suburban semis suggest. Three conservation areas carry the town's own name. There are about ninety listed buildings in the wider area. The clay underneath shifts everywhere. Neighbours file planning applications at a rate that suggests most of them got their extensions in the end.
There are 91 listed buildings across the wider area covered by this page. None is Grade I, 8 are Grade II* and 83 are Grade II. Listing protects the whole building, inside and out, so changes that would be routine on an ordinary house, from windows to internal walls, need listed building consent from Bromley council on top of any planning permission. Most buyers here won't own one of the 91. Anyone who does will spend more time on paperwork than on building.
The same wider area has 11 conservation areas, three of them named after Petts Wood: Station Square, The Chenies and Chislehurst Road. Inside a conservation area, the council judges changes partly on how they affect the look of the street. Work that counts as permitted development elsewhere, such as some front-facing alterations, cladding or a dormer facing the road, can need full planning permission. The council can also remove permitted development rights in specific areas. Check on Bromley council's planning pages whether the house is inside one of these boundaries and whether any of those rights have been taken away, because the answer can turn a weekend job into an eight-week application. The builders of the late 1920s had more freedom with these plots than their current owners do.
There are 4 scheduled monuments in the area, the strictest tier of heritage protection. They mostly matter to anyone whose land is next to one.
Bromley council received 1,063 planning applications across the area between April 2024 and June 2026, and 487 in the most recent twelve months. That doesn't show how many were approved. It does show that a lot of people here keep applying to change their homes, and some of them come back to apply again.
The British Geological Survey puts the ground under the whole area in class 3 for shrink-swell, a published hazard class for clay that swells when wet and shrinks when dry. For an extension, that means deeper foundations than you would need on sand or chalk, nearby trees taken into account, and a structural engineer's view before anyone digs. It is a well-known problem with known fixes, and they cost money. Build without them and you risk cracks in the new work.
Historic England's Heritage at Risk register lists one building in the area, a listed building in poor enough condition to be on the register. Repairs to it may qualify for grant support and will be closely examined. For the owner of an ordinary house down the road, it changes nothing.
In practice, outside the conservation areas and away from listed buildings, a standard rear extension or loft conversion on a semi may come under permitted development, subject to the usual limits and a check with the council. Inside the three Petts Wood conservation areas, assume anything visible from the street needs permission. Wherever you are, the clay sets the foundations.
Freedom to alter a home here is below average. The conservation areas and the clay add cost, time or both to most projects, though the planning figures show that people manage it.