Yes, in most of Cuffley you can extend under ordinary planning rules. Only a handful of buildings in and around the village are listed. None of them is above Grade II. The only conservation area belongs to the village next door. The thing most likely to argue with your extension is the clay under it.
There are five listed buildings in the area around Cuffley, all of them Grade II, with none at Grade I or Grade II*. Listing protects a building's interior and exterior, so changes to a listed home need listed building consent from the council on top of any planning permission, and that covers windows, doors and internal walls as well as extensions. With five in the area, almost every buyer here will own a house the listing rules never mention. Cuffley was a hamlet of a few cottages at the start of the twentieth century, and nearly everything since went up after the railway, long after anyone thought of listing it.
The area has one conservation area, Northaw Village. Conservation areas bring tighter control over demolition, trees and changes visible from the street, and some householder work that would otherwise go ahead without an application needs one inside the boundary. The council's map shows where the line runs, and it is a quick check for any house near Northaw. For a typical Cuffley semi, bungalow or detached house, the boundary is someone else's concern.
The neighbours have certainly not been sitting still. Welwyn Hatfield Borough Council's planning register logged 1,275 applications across the area between April 2024 and June 2026, and 581 in the last twelve months of that period. Those counts include everything from loft conversions to new garages, and the planning list tells you how many people applied, never how many got what they asked for. With that many applications, the bungalow next door is unlikely to stay a bungalow for long.
The ground is the part to plan for. The British Geological Survey puts Cuffley's shrink-swell hazard at class 3, and the whole of the area reaches that class. Shrink-swell clay swells when wet and shrinks when dry, and it can move foundations that are too shallow, particularly near thirsty trees. For an extension that means deeper footings than the original house may have and a structural engineer's view at the design stage. Building control will want to know about clay, and a design that planned for it from the start costs less than one changed halfway through.
In practice, most homes outside the conservation area and outside the five listed buildings can use the national permitted development rules for modest rear extensions, loft conversions and outbuildings, within the size limits those rules set. Anything bigger, or anything on the front of the house, goes through a normal householder application to the council. The council's planning portal holds the decision history for every address, and the decisions on a few nearby houses with the same layout are the best guide to what the officers will accept. The rules here are mostly the standard ones, and the main extra cost is the depth of the foundations.
Cuffley gives owners plenty of freedom to extend. Heritage barely gets in the way, and the clay is the one thing to budget properly for.