Yes. Perry Green is about as relaxed about extensions as a place with old houses gets. There are only four listed buildings. No conservation area reaches it. Neighbours put in planning applications all the time. Planning permission is the easy bit here, and the clay underneath is the harder one.
Historic England lists four buildings in Perry Green: none at Grade I, one at Grade II* and three at Grade II. Owning one of them means listed building consent for almost any change, inside or out, and Grade II* puts it among the more significant historic buildings, where the conservation officers look more closely. Buy any other house in Perry Green and none of that applies to you. With four listed buildings in the whole hamlet, you're unlikely to buy one without realising, and a conveyancer won't let it slip past anyway.
Between April 2024 and June 2026 there were 191 planning applications for the area, 73 of them in the last twelve months. That's plenty of evidence that people here alter their homes and go through the process to do it. What happened to those applications, approved or refused, the record doesn't consistently say, so the count shows how busy planning is here and nothing about the odds of getting approval.
The British Geological Survey puts the ground here in shrink-swell Class 3, and all of the area reaches that class. Shrink-swell is clay that swells when wet and shrinks when dry, and a new extension has to sit on foundations deep enough to ignore it. Expect a structural engineer to have an opinion on foundation depth, and expect the existing house and the new extension to need tying together with care. That's a matter for the budget, and nothing a buyer needs to fear.
Outside a conservation area and away from the listed buildings, many modest rear and side extensions fall under permitted development rights, which means no full planning application, within national size and height limits. Anything larger, or any house where those rights have been removed, goes through East Hertfordshire's planning process like everywhere else. The one check worth making is the planning history of the specific house: a condition attached to an earlier approval can quietly remove permitted development rights, and a buyer only finds out when the plans are already drawn.
Freedom to extend is one of Perry Green's real strengths: few listed buildings, no conservation area and an active planning record next door. The planning office won't be what slows you down. The foundations will.