Most single storey extensions in Swansea end up somewhere between £35,000 and £80,000, which is too wide a range to budget with. The gap comes down to size, specification and, more than people expect, the plot itself. Here is how the figures break down and what moves a quote on a Swansea house.
Builders usually price by the square metre of floor area. For a properly built single storey extension in the Swansea area, a realistic guide for the build is around £1,800 to £2,600 per square metre plus VAT. That covers foundations, walls, roof, insulation, windows and doors, plastering, and basic electrics and heating. A high-end finish with large glazed openings and a lot of structural steel can go past £3,000 per square metre.
As rough guides before VAT:
A build cost per square metre is rarely the whole bill. Check whether a quote includes the items below, because they are the usual reason two prices for the same job look very different.
Smaller extensions also cost more per square metre than larger ones. Setting up the site, digging foundations and knocking through the back wall cost much the same whether you add 12 square metres or 25.
Ground and access matter as much as the design. Sloping plots are common in Townhill, Mount Pleasant and parts of Sketty and Mumbles. They can mean stepped foundations, retaining walls and extra excavation, which can add several thousand pounds before a wall goes up.
Terraced streets in Uplands, Brynmill and Sandfields often have no side access, so materials and spoil are carried through the house or along a narrow rear lane. That adds labour time. Older terraces also tend to have shared drains running across the back gardens. Building over or close to one needs agreement from Dŵr Cymru Welsh Water, and sometimes a diversion.
Parts of Morriston, Llansamlet, Gorseinon and the wider former coalfield have a history of mining. An engineer may ask for a mining report or deeper foundations there. On exposed coastal plots around Mumbles and Gower, it is worth paying for better windows, fixings and roof coverings that cope with salt air and driving rain.
Many modest rear extensions fall under permitted development and do not need a full planning application, but the limits depend on your house and plot. Conservation areas such as parts of Mumbles, and homes within the Gower National Landscape, have tighter rules. Check with Swansea Council's planning department before you commit to a design.
Every extension needs Building Regulations approval, whether or not it needs planning permission. Allow several hundred pounds for each application. If you are building on or near a boundary with a neighbour, set aside something for a party wall surveyor too.
A firm price needs drawings. A builder quoting from a conversation in the garden is guessing, and those guesses tend to be corrected upwards once work starts. Get your plans and structural calculations done first, then ask each builder to price the same written specification.
Ask for an itemised quote showing what is included, what is a provisional sum and what is excluded. Keep a contingency of around 10 per cent, particularly on older Swansea properties where drains, ground conditions and existing walls are not fully known until the digging starts.
Most take around 10 to 16 weeks on site, depending on size, weather and how much work is needed inside the existing house. Allow extra time beforehand for drawings, approvals and any drainage agreements.
Not always, as many smaller rear extensions fall within permitted development. The rules are stricter in conservation areas and on Gower, so confirm with Swansea Council before work starts. Building Regulations approval is needed either way.
Usually yes. Most of the work happens outside until the opening is made into the existing house, though you should expect dust, noise and a spell without a working kitchen if that is the room being extended.