Yes, for most houses, with a couple of exceptions to check first. The village has a handful of listed buildings and one conservation area, and most homes sit outside both. The clay under every street matters more than either. The neighbours keep the planning office busy, which shows plenty of people get their extensions through. For most owners the bigger cost is foundations, more than the paperwork.
Elstree has 24 listed buildings: none at Grade I, 2 at Grade II* and 22 at Grade II. For those homes, listed building consent covers almost any change to the character of the building, inside as well as out, so an extension, new windows or a knocked-through wall all go to the council first. Work done without consent on a listed building is a criminal offence, and the duty to put it right passes to whoever owns it next. For the great majority of houses, built long after anything here was first listed, none of it applies.
The village has one conservation area, Elstree Village, covering the historic core. Inside it the council has firmer control over changes that can be seen from the street, and the size of extension a homeowner can build without an application is smaller. Hertsmere publishes the boundary on its own map, and checking it is worth a few minutes, because two houses on the same road can fall on different sides of the line. The village name goes back to Tidwulf's tree, and nobody needed consent to plant that.
The planning records show how much building goes on. In the area's records there were 1,036 applications between April 2024 and June 2026, 441 of them in the last twelve months. That is a busy planning list for a village, made up of rear extensions, loft conversions and the steady job of making post-war houses bigger. Elstree's homeowners are, on this evidence, constantly building.
The ground is the bigger issue. On the British Geological Survey's shrink-swell measure, the area's highest class is 3, and every part of the area reaches it. Clay that swells when wet and shrinks when dry moves foundations, and nearby trees make it worse by drawing water out of the soil. For an extension that means deeper foundations, sometimes considerably deeper, and a structural engineer's view before the builder prices the job. Building control will expect it either way. Most of the extra cost of extending here goes into the ground.
For a typical Elstree house outside the conservation area and not listed, many single-storey rear extensions and loft conversions can go ahead under permitted development rights without a full planning application, within national size limits. A listed house or one in the Elstree Village conservation area needs consent much earlier. The clay has to be dealt with under building regulations whichever route applies.
Elstree gives an owner a middling amount of freedom. Most houses are fairly free above ground, a protected few are not, and the clay underneath slows every project down.