A side extension is often the easiest way to add space to a Peacehaven home, especially on the wider plots and bungalows common across the town. Costs vary a lot, so this guide covers what you are actually paying for, the ranges people tend to see, and the things that push a budget up or down.
For a single storey side extension built to a good standard, most Sussex projects come in at roughly £1,800 to £2,800 per square metre for the build itself. On a common size of around 3m wide by 6m deep (18 square metres), that usually works out at somewhere between £35,000 and £60,000 before kitchen units, bathroom fittings or high-end finishes.
A two-storey side extension costs more overall, but the price per square metre often drops a little, because the foundations and roof are shared across two floors. Treat all of these figures as a starting point. The real number depends on your house, your ground and your specification, which is why a site visit and a written quote matter more than any online average.
Two side extensions of the same size can differ in price by tens of thousands of pounds. The main factors are:
Peacehaven falls under Lewes District Council for planning. Many single storey side extensions can go ahead under permitted development, as long as they are no more than 4m high and no wider than half the width of the original house. Two-storey side extensions, and anything that falls outside those limits, generally need full planning permission. Rules change and every property is different, so check before you commit, or apply for a lawful development certificate for peace of mind.
Whichever route applies, you will need building regulations approval. Budget separately for drawings, structural calculations, building control fees and possibly a party wall agreement if you are building close to or on a shared boundary. Together these can add several thousand pounds to the project.
Peacehaven is exposed to strong winds and salt air off the Channel, which is worth bearing in mind when choosing materials. Good quality render, properly detailed roof edges and sound pointing help a new extension stand up to the weather and match the existing house.
A typical single storey side extension takes around 10 to 16 weeks on site once work starts, depending on size and weather. Groundworks and foundations come first, then the walls, roof and the knock-through, followed by plastering, electrics, plumbing and heating. Using one team throughout helps avoid gaps between trades, which is where many projects lose time.
Get a clear, itemised quote that states what is and is not included, such as skips, steelwork, decorating and making good. Set aside a contingency of 10 to 15 percent for surprises, particularly once the ground is opened up.
Decide on doors, windows and the layout early, because changes mid-build are among the most common causes of rising costs. If you are a self-builder handling some of the work yourself, hiring a mini digger and having aggregates delivered to site can make the groundworks stage quicker and easier to plan.
Many single storey side extensions fall under permitted development, provided they are no higher than 4m and no wider than half the original house. Two-storey side extensions usually need full planning permission from Lewes District Council.
Not necessarily, as the cost per square metre is similar. Side extensions can cost more if access is tight, if services need moving or if a large opening needs a steel beam.
Most people do, as the majority of work happens outside until the knock-through. Expect some dust and disruption for a short period when the existing wall is opened up.
Tell us what you are planning and we will come and take a look. Free, no-pressure quotes across Brighton and Sussex.