Yes, you can extend a house in most of Romford, and the conservation areas are where the rules get stricter. Only a couple of dozen buildings are listed. Three conservation areas reach into the area. The clay underneath most of the area matters more than the paperwork. For most homes the planning side is routine, and the ground is the bigger cost.
There are 26 listed buildings in the area: none at grade I, one at grade II* and 25 at grade II. Listing covers the whole building, inside and out, so changes that would affect its character need listed building consent as well as any planning permission, and the bar for granting it is high. Romford is first recorded in 1177, and in all that time it has kept just 26 listed buildings, which is very little red tape for a town that old.
Three conservation areas reach into the area: Gidea Park, Romford, and St Leonard's, Hornchurch. Inside them, the council looks more closely at anything that changes a building's outside, and some work that would be routine elsewhere needs a full application. The Gidea Park area grew out of the Romford Garden Suburb, built in 1910 and 1911, so inside it you're dealing with Edwardian planners who decided what the streets should look like, and the council still holds to it. Whether a house sits inside one of the three boundaries is the one thing to check on Havering Council's conservation area maps, because the line can split a street, and the work you can do changes from one side to the other.
There is one scheduled monument in the area, the strictest tier of protection, and it matters mainly to anyone whose land is next to it.
Plenty of people do extend. Havering Council logged 643 planning applications in the area between April 2024 and June 2026, 249 of them in the last twelve months. Plenty of the neighbours have already put in for their own extensions.
The ground matters as much as the paperwork. The British Geological Survey rates the area's shrink-swell hazard at class 3, the highest class found here, and the whole area reaches it. Clay that swells when wet and shrinks when dry can move shallow foundations, especially near trees. In practice, that means getting a structural engineer to look at the ground before any extension, and possibly digging deeper foundations than a builder would quote by default. The north of the town is built on London Clay, and it's the clay, more than the council, that will have the biggest say on a rear extension.
Outside the conservation areas and away from the listed buildings, many ordinary rear extensions and loft conversions can go ahead under permitted development, the national rights that let homeowners build within set limits without a full application. Inside a conservation area, or on a listed building, expect to apply and expect closer scrutiny. Flats don't have the same permitted development rights as houses, so changing a flat usually means an application whatever the address.
Freedom to extend in Romford is middling. Most streets are straightforward on planning, the conservation areas are stricter, and the clay sets the cost of the foundations everywhere.