Yes, in most of Borehamwood, though the clay under the town has its say. Listed buildings are rare. There is only one conservation area within reach. The neighbours file planning applications at a steady clip. The town's heritage is a light constraint, and its geology is a heavier one.
Borehamwood and its immediate surroundings hold 42 listed buildings, two of them Grade II* and the other 40 Grade II, with none at Grade I. Listing covers the inside of a building as well as the outside, so altering one usually needs listed building consent on top of any planning permission, and changes that would be routine elsewhere get looked at line by line. With 42 such buildings in a town of post-war estates, the odds of buying one by accident are slim. Anyone who does will know it, because the particulars rarely leave it out.
One conservation area falls within the area, Elstree Village, and it covers the old village core at the edge of town, away from the main estates. Inside a conservation area, changes that would normally go ahead without an application, such as some demolition, cladding or work affecting trees, can need consent, and the council judges new work by how it fits the character of the place. For most of Borehamwood's streets, a conservation officer is someone who works in Elstree.
The planning register records 4,310 applications across the area between April 2024 and June 2026, and 1,877 in the most recent twelve months. Those figures count requests, with no record of how they were decided, but they show plenty of people trying to change their homes. Hertsmere's planning list is the kind of thing residents read with a cup of tea, and the people next door are very likely on it. It is worth looking up a house's own history on the council's register too, since an earlier extension can use up some of the rights a new owner was counting on.
The ground is the more serious constraint. The British Geological Survey puts Borehamwood in class 3 for shrink-swell clay, and the whole area reaches that class. Clay that swells when wet and shrinks when dry moves foundations, so an extension here usually needs deeper footings than on sand or chalk, and a structural engineer's view before the builder quotes. Nearby trees can make it worse, because they draw water out of the clay. None of this rules out building. It changes the price of a single-storey rear extension, and the borehole tends to settle the budget argument before the architect does.
For most semis and terraced houses outside the conservation area, a modest rear extension or loft conversion can often go ahead under permitted development, with no full application. Some projects need prior approval, and anything larger or on the front needs planning permission. Listed buildings and homes in Elstree Village sit outside the simpler route, and the clay has to be dealt with under building regulations whichever way the planning goes.
Borehamwood gives owners middling freedom to extend. The planning rules mostly stay out of the way, and the clay is the part that tends to cost money.