Yes, you can extend most homes in Greenford, but the clay underneath and the heritage map both get a say. Most of the houses are interwar and not listed. Even so, there are dozens of listed buildings and ten conservation areas in and around the town. Across most of the area the clay shrinks in dry weather and swells in wet. Planning permission is usually the easy part, and the ground is where an extension gets expensive.
Historic England lists 44 buildings in and around Greenford: three at Grade I, six at Grade II* and 35 at Grade II. If a building is listed, almost any change that affects its character needs listed building consent on top of any planning permission, and that covers the inside as well as the outside. Grade I and II* buildings are watched most closely. On an ordinary interwar semi none of this applies, but if your house is on the list, it shapes every decision you make about it.
Ten conservation areas fall within the wider box drawn around Greenford, among them Canalside along the Grand Union Canal and Brentham Garden Estate. Inside a conservation area, changes to roofs, windows, frontages and trees get more attention from the council, and some work that is automatically allowed elsewhere needs an application. Ealing Council's conservation area maps show the boundaries, so you can check which side of one a particular house is on.
There are three scheduled monuments in the area, the strictest tier of protection, including an Iron Age settlement on Horsenden Hill. They matter mainly to land right next to one.
People do extend here, and in large numbers. Ealing recorded 1,330 planning applications in Greenford between March 2024 and June 2026, 545 of them in the last twelve months. For many households on these streets, building out the back has clearly looked easier than moving house.
The ground is the bigger constraint. The British Geological Survey gives Greenford's shrink-swell hazard a top class of 3 on its published scale, and about 71% of the area reaches that class or above. Clay at that level moves with the seasons, so an extension usually needs deeper foundations than a builder might quote at first, and a structural engineer should see the plans. The roots of a nearby tree can make the movement worse. Clay that swells in a wet winter and shrinks in a dry summer will move a new extension whether or not the council approved it.
One listed building in the area is on Historic England's Heritage at Risk register. That means it is in poor condition. Repairs to it may qualify for grant support and will be closely examined. For the owner of an ordinary house nearby, it changes nothing.
Outside a listed building or a conservation area, many modest rear extensions and loft conversions can go ahead under permitted development, which needs no full planning application. Inside a conservation area that allowance shrinks, and on a listed building it largely disappears. Either way, building regulations still apply to the foundations.
Greenford gives you less freedom to extend than its plain interwar streets suggest. The heritage rules only cover pockets of the town, but the clay is under most of it.