For most of Boreham, yes. Most of the houses are post-war semis with no special heritage protection. A small number of old buildings are listed. Two conservation areas bring extra rules. For most extensions here, the clay under the house will take more thought than the planning paperwork.
Historic England lists 18 buildings in Boreham. One is Grade I, one is Grade II* and the other 16 are Grade II. Listing protects the whole building, inside as well as out, so changing anything structural, from windows to internal walls, needs listed building consent on top of any planning permission. Owners of those 18 know who they are. Most of the village was built during a programme of house-building in the mid-1970s, and nobody has listed any of that yet.
Boreham has two conservation areas, Boreham Church Road and Boreham Roman Road and Plantation Road. A conservation area doesn't stop you extending a house, but it narrows what you can do without asking, and the council will look harder at anything visible from the street. On Church Road, the council will take a close interest in your front elevation.
People clearly do extend and alter their homes around here. The planning register covering the area logged 2,215 applications between April 2024 and June 2026, and 1,008 of them came in the last twelve months. Whatever else Boreham's planning department is short of, it isn't paperwork.
The bigger issue is the ground. The British Geological Survey puts the area in class 3 for shrink-swell clay, and all of Boreham reaches that class. The clay swells when it gets wet and shrinks when it dries out, and nearby trees make both worse. For an extension, that usually means deeper foundations than a standard design would assume and a structural engineer's view before the builder prices the job. Ask building control what foundation depth it expects near any trees on the plot you're looking at. The clay doesn't care whether the house is in a conservation area.
One listed building in the area is on Historic England's Heritage at Risk register. That means it's in poor condition, so its repair may qualify for grant support and will be watched closely by Historic England. It's a matter for that building's owner, and it has no effect on a semi three roads away.
In practice, a semi or a detached house outside the two conservation areas can usually take a modest rear extension or a loft conversion under permitted development rights, which allow certain work without a planning application. Inside a conservation area those rights are narrower, and a listed building needs consent for almost everything. Chelmsford's planning department will confirm which applies to a given address, and a lawful development certificate puts that answer in writing.
Overall, Boreham gives owners about average freedom to extend. Most homes can grow without much trouble, a handful of streets need the council's agreement first, and the clay affects every extension wherever it's built.