Most people start with a figure they found online, then get a quote that looks very different. Extension costs in East Devon depend heavily on your house, your plot and the planning rules where you live. Here is an honest guide to what homeowners from Exmouth to Honiton are paying in 2026, and why.
Most builders price an extension per square metre of new floor space. In East Devon in 2026, a well built single storey extension usually works out at around £2,200 to £3,200 per square metre before VAT. That covers foundations, walls, roof, windows, basic electrics, plastering and a decorated shell ready for fitting out.
A two storey extension often costs a little less per square metre, because the foundations and roof are shared across two floors. Even so, the total bill is higher. Kitchens, bathrooms and high end glazing are usually priced on top of the shell.
The build is only part of the budget. Allow for professional and statutory costs before anything happens on site. Leaving these out is the most common reason projects go over budget.
We also recommend keeping a contingency of 10 to 15% for surprises. Older properties in places like Budleigh Salterton and Sidmouth are the most likely to need one. Hidden drains, weak lintels or old wiring often only turn up once walls are opened up.
Many single storey rear extensions can be built under permitted development without a full planning application. The usual limits are up to 3 metres deep on a semi detached or terraced house, or 4 metres on a detached house. Larger rear extensions may be possible through the prior approval process.
East Devon has more restrictions than many areas. Large parts of the district sit within the East Devon National Landscape (formerly the AONB). Towns including Budleigh Salterton, Sidmouth and Ottery St Mary also have conservation areas. In these places side extensions and some external materials usually need full planning permission. The council may also ask for materials that match local stone, brick or render, which can add to the cost. Listed buildings need listed building consent for almost any change.
Ground conditions matter. Sloping gardens, clay soils and tree roots can mean deeper or specialist foundations. These can add several thousand pounds on their own. Access matters too: narrow lanes and terraced streets with no side access can mean materials go through the house or by hand, which takes longer.
Coastal homes need materials that cope with wind driven rain and salt air. That means good quality render, stainless fixings and well specified windows. Big glazed openings, bi-fold doors and vaulted ceilings with roof lights all add cost quickly. A simple rectangular extension with a standard pitched or flat roof is the most economical shape to build.
Ask for an itemised quote based on proper drawings, not a figure per square metre. Check what is included: groundworks, drainage, electrics, plastering, flooring and decoration are often where quotes differ. A builder who visits, looks at your access and ground, and asks about your plans will give you a far more accurate price than any online calculator.
Not always. Many single storey rear extensions fall under permitted development. However, if your home is in a conservation area, the National Landscape or is listed, you are more likely to need full permission, so check with East Devon District Council or your designer first.
A single storey extension usually takes around 10 to 16 weeks on site, and a two storey extension 16 to 24 weeks. Allow extra time beforehand for drawings, planning and Building Control approval.
For many East Devon homeowners, extending works out cheaper once stamp duty, estate agent fees, legal costs and removals are added up. It depends on how much space you need and whether the extension adds value in line with what it costs to build.
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