Yes, and with fewer rules in the way than in most old villages. No conservation area covers any of it. Only about a dozen buildings are listed. One scheduled monument is the strictest protection anywhere near. The clay under the houses has more say over your extension than the conservation officer does.
Eleven buildings in and around Kelvedon Hatch are listed: none at Grade I, one at Grade II* and ten at Grade II. Listing protects the whole building, inside and out, so almost any change to one of them needs listed building consent on top of ordinary planning permission, and the officers will care about the details. For everyone else, eleven is the whole list, and the chances that the house you're viewing is on it are small. One phone call to Brentwood's planning department settles it.
There is one scheduled monument nearby. It's the strictest tier of protection, and it only matters if your plot sits right next to it.
The planning records covering the area show 1,643 applications between April 2024 and June 2026, 726 of them in the last twelve months. That is a steady stream of people asking to change their houses. Ask the seller for the planning history of the house itself: any consent granted to a previous owner, and any condition attached to it, comes with the house when you buy it.
The British Geological Survey puts the ground here in shrink-swell class 3, and the whole area reaches that class. In plain terms, the clay swells when it's wet and shrinks when it's dry, so it pulls at shallow foundations, especially near thirsty trees. For an extension that usually means deeper foundations than a builder working on sand would dig, and a structural engineer looking at the soil and the trees before the design is fixed. Building control will ask about it anyway. The clay sets the depth of the hole, and that comes out of your budget, not out of whether you can build at all.
With no conservation area and very few listed buildings, most homes keep their full permitted development rights, so a modest single-storey rear extension or a loft conversion within the national size limits can often go ahead without a full application. Anything larger goes to Brentwood's planners, and the Metropolitan Green Belt around the village makes them careful about bulk on the edges. The village's most drastic alteration on record was Great Myles, largely demolished in 1837, and a few of its outbuildings are all that remain. Your extension will face more paperwork than that demolition did, but not much more.
Freedom to alter your home is one of Kelvedon Hatch's real advantages. Outside its handful of listed buildings, the main limits are the size rules and the clay.