You can extend most houses in Heston, though with more paperwork than a suburb of interwar semis would usually need. There are forty listed buildings in and around it. Seven conservation areas overlap its edges. A third of postcodes sit on clay that moves. Heston is mostly an ordinary suburb, but the parts that aren't ordinary come with an unusual number of rules.
There are 40 listed buildings in and around Heston. Four are Grade I, two are Grade II* and 34 are Grade II. Owning one means getting listed building consent for almost any change that affects its character, inside or out, and the council and Historic England both take an interest in the Grade I and Grade II* entries. Four Grade I buildings is a lot of national importance in a district that was mostly market gardens until the 1920s, and the houses next to them inherit some of the attention.
The area overlaps seven conservation areas: Heston Village, Norwood Green, Cranford Village, Cranford Park, Osterley Park, Hounslow Cavalry Barracks and St Paul's Church. Inside them, works that would be routine elsewhere, including some extensions, roof changes and demolition, need the council's consent, and the council will look at materials and appearance as well as size. A rear extension that goes through without trouble on an interwar estate can take months of letters about brick colour in Heston Village.
The neighbours are extending anyway. The council logged 784 planning applications in the area between March 2024 and July 2026, 279 of them in the last twelve months. That is a steady flow of lofts, side returns and rear extensions on a suburb of semis, and a buyer who wants the fourth bedroom will be joining a long queue of people who wanted the same thing.
The ground needs as much thought as the planning. The British Geological Survey rates Heston's clay at class 3 for shrink-swell, its highest class here, and 34% of postcodes reach it. Clay like this swells when wet and shrinks in dry summers, so extension foundations usually have to go deeper than on sand or chalk, and trees near the build matter more. Get a structural engineer to look at the soil and the trees early, because the foundation design will move the builder's quote more than the planning application will.
Three listed buildings in the area are on Historic England's Heritage at Risk register. They are buildings in poor condition. Repairs to them may get grant funding, and they will get close scrutiny. None of that affects the owner of an ordinary semi down the road, except as a reminder that the council keeps a close eye on the old buildings here.
In practice, a house outside the conservation areas can often take a modest rear extension or a loft conversion under permitted development, without a full planning application, as long as it stays within the national limits. Flats have no permitted development rights, so any change to one needs consent. The useful check is to ask the council whether the house is inside a conservation area and whether permitted development rights have been removed for it, because the answer decides whether an extension is a builder's job or an application.
Heston gives a homeowner less freedom to extend than its rows of interwar semis suggest. The conservation areas, the listed buildings and the clay all add work to a project, so most extensions here need permission, a structural engineer, or both.