If you need more space, the choice usually comes down to building out with a single storey extension or building up and out with a double storey. Neither is automatically better, but one will almost certainly suit your house, budget and garden more than the other. Here is how we help homeowners across Swansea and South Wales decide.
A single storey extension in the Swansea area typically comes in somewhere between £2,000 and £2,800 per square metre, depending on specification, ground conditions and how much glazing you want. Kitchens and bathrooms push the figure up because of plumbing, electrics and fittings.
A double storey extension costs more in total, but noticeably less per square metre, often 20 to 30 percent less for the upstairs space. That is because the expensive parts, the foundations and the roof, are shared across two floors. So if a 20 square metre single storey costs around £50,000, adding the second storey might only add £25,000 to £30,000 rather than doubling the bill. If you genuinely need the extra bedroom or bathroom, building up is usually the better value.
Single storey rear extensions can often be built under permitted development rights in Wales, up to 3 metres deep on an attached house or 4 metres on a detached one, with a maximum height of 4 metres. That means no full planning application, which saves time and removes some uncertainty.
Double storey extensions almost always need full planning permission from Swansea Council. Officers will look closely at overlooking, loss of light to neighbours and how the extension sits against the original roofline. On many local streets, particularly the terraced and semi-detached stock in areas like Sketty, Morriston and Uplands, a well designed two storey rear extension is perfectly achievable, but expect the process to take 8 to 12 weeks and budget for drawings and application fees.
A single storey extension transforms how the ground floor works. It is the right choice if your priority is a bigger kitchen, a dining space that opens onto the garden, or a downstairs WC and utility. It also suits homes where the garden is generous, because you can afford to give up 15 to 25 square metres of it without the outside space feeling cramped.
A double storey extension is the answer when the problem is bedrooms as much as living space. Growing families who love their street but have outgrown a three bed often find that adding a fourth bedroom and second bathroom above a kitchen extension costs far less than moving, once you factor in land transaction tax, estate agent and legal fees. The trade-off is a longer build, typically 4 to 6 months against 10 to 14 weeks for a single storey, and more disruption while the roof and upper floor are tied into the existing house.
Start with what your household will need in five years, not just today. If the ground floor is the squeeze, build out. If you are one bedroom short, or will be, the shared foundation cost makes building up hard to ignore.
Then look at your specific plot. Foundations near drains or on made-up ground, which is common in parts of Swansea, can add cost to either option, and an awkward roof junction can complicate a double storey. A builder or architect who has worked on similar local houses can usually tell you quickly which route your property lends itself to, so get someone to look before you commit to drawings.
Often yes, if you need the upstairs space. Because foundations and roof are shared, the second floor is much cheaper per square metre than the first, and an extra bedroom typically adds more to a valuation than the same spend downstairs.
Not always. Many single storey rear extensions fall under permitted development in Wales if they stay within size and height limits, but it is worth applying for a lawful development certificate for peace of mind, and some properties have restrictions, so check with Swansea Council first.
Usually, yes. For a single storey extension most of the work happens outside the existing walls until the final knock-through. A double storey build is more disruptive, especially when bedrooms are affected, but most families stay put with some planning around the messiest weeks.