Mostly, yes. There are few listed buildings. The conservation areas are in the older villages and along the canal. Most of the heath is post-war housing that nobody saw any reason to protect. The ground under your extension will have more say than the council.
Iver Heath and the surrounding area hold 57 listed buildings: one at Grade I, three at Grade II* and 53 at Grade II. Listing covers the whole building, inside and out, and any alteration that affects its character needs listed building consent on top of any planning permission. Doing the work without consent is a criminal offence. That matters to the owners of those 57 buildings. For the far larger stock of post-war semis and detached houses around them, listing doesn't come into it.
There are six conservation areas in the surrounding area, including Iver itself and stretches of the canal at Cowley Lock and Uxbridge Lock. Inside a conservation area, some extensions that would otherwise go ahead without an application need full planning permission, and the council will judge the design against the character of the area. Check the council's conservation area map early: whether a home is inside or outside the boundary decides how the whole project goes.
There is one scheduled monument in the surrounding area. Scheduling is the strictest protection there is, and it matters mainly to anyone whose land lies close to the monument.
Buckinghamshire Council received 2,018 planning applications across the Iver Heath area between April 2024 and June 2026, including 926 in the last twelve months. That figure counts applications only and says nothing about how many were approved, but it shows that plenty of people here are altering their homes. It looks like an area full of semis whose owners would like a detached house.
The bigger issue for an extension is the ground. The British Geological Survey rates shrink-swell clay at its class 3 across about 45% of the area. Clay at that class swells when wet and shrinks in dry summers, and a new extension on shallow foundations can move independently of the house it is attached to. Building on it usually means deeper foundations, and a structural engineer should assess the ground at the design stage, along with any large trees near the planned footprint. The last big rebuild on record at Richings Park followed a fire that burned the house down in the 1780s, and the council would not recommend that route.
For most homes in Iver Heath, a modest rear extension or a loft conversion can be done under permitted development, the national rules that allow some building work without a planning application, provided the house is outside a conservation area, isn't listed and hasn't had those rights removed. Anything larger, or anything inside the protected areas, needs an application to Buckinghamshire Council. A lawful development certificate from the council confirms in writing that a project falls within permitted development, which helps when the house is sold later.
Iver Heath sits in the middle for freedom to extend. Planning is unlikely to stand in your way, but the clay will affect the foundations and the cost.