Yes, in most of South Ockendon you can. There are no conservation areas. Only a small number of buildings are listed. The neighbours have been sending in planning applications at a steady rate. The planning rules are relaxed here, so the clay under the town is the bigger obstacle.
Historic England's register includes 17 listed buildings across the area. One is Grade I, two are Grade II* and 14 are Grade II. Listing means almost any change that affects a building's character, inside or out, needs listed building consent on top of any planning permission, and the duty applies to the owner of the building. With 17 listed buildings among thousands of homes, most of them post-war, the chance of buying one by accident is small.
The area also has two scheduled monuments, the strictest form of heritage protection. Work on or near them needs consent from the government, but this mostly matters to whoever owns the land next to them.
Thurrock Council's register shows 429 planning applications for the area between April 2024 and June 2026, with 202 of them in the last twelve months. That doesn't say how many were approved, but it shows plenty of residents are getting plans drawn up. On terraces built in uniform rows, an extension at the back is often the first visible sign that someone has moved in.
The British Geological Survey's ground-stability mapping puts the whole area in class 3 for shrink-swell clay. That means clay soils that expand when wet and shrink when dry, enough to move shallow foundations. It doesn't stop anyone extending, but it does affect how the extension is built. Expect deeper foundations than a builder from elsewhere might quote, and get a structural engineer's view on the foundation design early. A quote that hasn't allowed for the clay is the kind most likely to grow once work starts.
One listed building in the area is on Historic England's Heritage at Risk register. That means its condition is poor enough to be watched, and repairs may qualify for grant support and will be checked closely. It matters to whoever owns that building. For anyone extending an ordinary semi nearby, it makes no difference.
With no conservation area, houses across South Ockendon get the standard national allowances that let smaller rear extensions and loft conversions go ahead without a full planning application. Anything bigger goes to Thurrock Council, as it would almost anywhere. Flats are more restricted, because most changes to the outside of a block need permission and the freeholder's agreement. With about three in ten homes here being flats, many buyers have less freedom than a house owner would. Check whether a past extension on the house you're buying went through the council's building control and was signed off. The lack of heritage rules makes unrecorded work more tempting.
South Ockendon is one of the easier places to extend a house. Heritage rules rarely get in the way here, so the main things to plan for are the clay and the cost.