Yes, most houses in New Cross can be extended, and the heritage rules reach fewer of them than the area's age might suggest. Under a hundred buildings are listed. The conservation areas lie out towards Nunhead. One scheduled monument turns up nearby. The ground and the fact that most homes are flats will shape a project more than any listing.
There are 96 listed buildings in and around New Cross: one at grade I, 15 at grade II* and 80 at grade II. Listing covers the whole building, inside and out, so changing one needs listed building consent from the council as well as any planning permission, and the two higher grades get the closest attention from Historic England. For a house that is not on the list, none of that applies.
The two conservation areas in the wider box drawn round New Cross are Nunhead Cemetery and Nunhead Green. Homes inside a conservation area face tighter rules on demolition, trees and changes visible from the street, and some works that would be automatic elsewhere need an application. The residents of the first one have not filed for an extension in some time.
The same wider box contains one scheduled monument, the strictest tier of protection, which matters mainly to anyone whose land touches it.
Lewisham's planning register logged 565 applications for New Cross between April 2024 and June 2026, and 197 of them in the last twelve months. Somebody in New Cross is putting in plans for something most weeks of the year.
The British Geological Survey puts the whole of New Cross in shrink-swell class 3, so every part of the area reaches that class. Ground in that class swells when wet and shrinks when dry, which affects how deep an extension's foundations need to go and how close they can sit to trees. A structural engineer's view on foundation depth for the exact plot is worth paying for at the design stage, since a deeper trench costs less to plan for than to discover.
One listed building in the area is on Historic England's Heritage at Risk register. That marks a building in poor condition, whose repair can attract grant money and will certainly attract scrutiny, and it makes no difference to the owner of an ordinary house down the road.
For a house outside the conservation areas and off the list, many rear extensions and loft conversions can go ahead under permitted development, within the national size limits. Flats are a different matter. They do not carry the same permitted development rights, so most changes need a full application, and a leasehold flat usually needs the freeholder's consent as well. In an area where most homes are flats, that is the rule most buyers will run into.
Freedom to extend in New Cross is middling: a house off the list and outside the conservation areas has room to grow, while the listed buildings, the flats and the clay each add their own paperwork.