You can usually extend a house in Colindale, as long as you get the ground and the paperwork right first. Listed buildings are few here, and almost all of them are Grade II. Three conservation areas reach into the district. Neighbours file planning applications all the time. The clay soil under every postcode is the bigger obstacle.
There are 56 listed buildings in and around the area: one Grade I, two Grade II* and 53 Grade II. Listing protects the whole building, inside and out. Most changes need listed building consent on top of any planning permission, and carrying out works without it is a criminal offence, not just a planning dispute. For the great majority of homes in Colindale, none of this applies.
Three conservation areas fall within the area's bounds: Hendon Church End, Hendon The Burroughs and the Watling Estate. Inside them the council takes a closer interest in front elevations, roofs, materials and anything that changes the street scene, and some work that would be routine elsewhere needs an application. The Watling Estate is a reminder that conservation status can cover a whole estate of houses, not just old churches and village greens.
Between April 2024 and June 2026 the council logged 1,203 planning applications in the area, 470 of them in the last twelve months. Neighbours here extend, convert and rebuild their homes all the time. Until the twentieth century Colindale was a farm, a large house and a few cottages, and it has kept building ever since.
The ground is a more common problem than heritage. The British Geological Survey rates every postcode in the area at class 3 for shrink-swell, the hazard where clay swells when wet and shrinks when dry. That is a published geological class, and it is no reason to panic. In practice an extension here usually needs deeper foundations than on stable ground, and nearby trees matter because their roots dry the clay out. Get a structural engineer's view on the foundation design early, before a builder's quote is settled.
Four listed buildings in the area are on Historic England's Heritage at Risk register. Those are buildings in poor repair that may qualify for grant help and will certainly get close attention from the council and Historic England. They are a problem for whoever owns them, and owning an ordinary house nearby doesn't make them yours.
How free you are depends on what kind of home you own. A house outside the conservation areas can often take a modest rear extension or a loft conversion under permitted development, the national rules that allow certain work without a full application. Flats have no such rights, and about 58% of homes on the council-tax list are flats, so for most owners any change means a planning application and the freeholder's written consent. If you own a house, a lawful development certificate from the council will confirm in writing that the work falls within permitted development.
Your freedom to extend in Colindale is middling. Heritage rules affect only a few streets, while the clay affects every plot.