Yes, you can extend a house in Hayes, but your freedom to do it is limited. There are 155 listed buildings in and around the area. Nineteen conservation areas overlap it. The clay under the houses is a reason to get a structural engineer involved early. Your neighbours are submitting planning applications at a steady rate, so extensions do get done here, with the paperwork that comes with them.
Historic England lists 155 buildings in and around Hayes. Six are Grade I, nine are Grade II* and the other 140 are Grade II. Listing covers the inside of a building as well as the outside, so a new kitchen layout or a replacement window in a listed house needs listed building consent from the council as well as any planning permission. The protection applies whatever the grade, and owners have been prosecuted for work done without consent.
The bounding box around the area takes in 19 conservation areas, among them Hayes Village, Keston Village, Bromley Common, and Bromley, Hayes and Keston Commons. Inside a conservation area, the council controls demolition, changes to front elevations and work to trees much more closely, and some of the work that would need no application elsewhere does need one here. Look up the address on Bromley council's conservation area maps, and ask the seller about any work they have already carried out under those rules.
Four scheduled monuments are also within that wider box. Scheduling is the strictest level of heritage protection, though it mainly matters if your garden backs onto one.
Plenty of people still extend their homes. Bromley council received 1,338 planning applications covering the area between April 2024 and June 2026, and 597 of them came in the last twelve months. Neighbours here are used to reading each other's plans, and someone will probably be watching yours.
Under most of Hayes the ground is clay that shrinks and swells. The British Geological Survey puts the shrink-swell hazard at class 3, the moderate level, across all of the area. Clay shrinks in a dry summer and swells in a wet winter, and large trees near a house make the movement worse. An extension on this ground will usually need deeper foundations than the builder's first quote assumes, so ask a structural engineer and get a soil report before the design is settled.
Seven listed buildings in the area are on Historic England's Heritage at Risk register. These are buildings in poor condition. Repairs to them may qualify for grant support, and any work on them gets close scrutiny. They make no difference to the owner of an ordinary semi down the road.
On an unlisted house outside a conservation area, many modest rear extensions and loft conversions come under permitted development, which needs no full planning application. In a listed building or a conservation area, much of that work needs consent, as does anything on a front elevation. Check with Bromley council which category your address falls into, because the answer decides how long and how expensive the project will be.
Hayes is more restrictive than most suburbs. An ordinary post-war semi can usually be extended, but the more historic the house or the street, the more consents you will need, and the clay means every extension will need proper foundations.