Yes, you can extend a house in Hillingdon, but more of the area comes with heritage rules attached than its suburban look suggests. There are well over a hundred listed buildings nearby. A dozen conservation areas. Three scheduled monuments. Clay under a good part of it. The semi looks easy to extend, and Hillingdon's paperwork is less easy-going.
Historic England lists 161 buildings in and around Hillingdon. Four are grade I, nine are grade II* and 148 are grade II. Listing covers the inside of a building as well as the outside, so almost any change to a listed house needs listed building consent on top of any planning permission. That goes for a new window, a moved wall or a different roof tile. Grade II covers most of them, which still means the council gets a say over your kitchen units if they come attached to a historic wall.
Twelve conservation areas fall within the same wider area, Hillingdon Village and Ickenham Village among them, along with the canal-side areas at Cowley Lock and Uxbridge Lock. In a conservation area, work that would go ahead without permission elsewhere can need consent, especially anything on the front of the house, and taking down a tree or a wall becomes a conversation with the council. The village names give it away. Wherever "Village" appears on the council's map, the planning officer has a view on the front of the house.
The wider area also contains three scheduled monuments, the strictest protection there is, and they matter mainly to anyone whose land runs up to one.
People here alter their homes anyway, and in large numbers. Hillingdon council received 922 planning applications for the area between April 2024 and June 2026, 372 of them in the last twelve months. Whatever extension you have in mind, the council's planning register will show several on nearby roads to read through first.
Ground conditions are the other constraint. The geological survey rates Hillingdon's ground at class 3 for shrink-swell at worst, and about 29% of the area reaches that class. Shrink-swell is clay that expands when wet and shrinks in dry spells, which moves foundations that are too shallow. For an extension it means deeper footings and a structural engineer's view early, especially near big trees. The kitchen extension costs more below ground than a buyer expects, and the clay is the reason.
Seven listed buildings in the area are on Historic England's Heritage at Risk register. These are buildings in poor condition. Their repair can attract grant money and will certainly attract scrutiny, and they make no difference to the owner of an ordinary house down the road.
In practice, an unlisted house outside a conservation area can often go ahead under permitted development, the national rules that let modest extensions and loft conversions skip a full planning application. A listed house always needs consent. A house inside a conservation area will often need it for anything visible from the street. The council's conservation area maps settle which group a house falls into, so read them before planning the work around the house.
Freedom to extend is below average in Hillingdon. The ordinary suburban streets leave reasonable room for a rear extension or a loft, but the old village cores and the clay make sure nobody does it cheaply or without being noticed.