Most single storey extensions in Dorset never go near a planning application, but the ones that do usually fail because of a boundary line, a roof height or a conservation designation nobody checked at the start. The rules are national, yet how they land on your house depends heavily on where you sit in Poole, Bournemouth or rural Dorset. Here is what actually determines the answer for your property.
Single storey rear extensions are usually covered by permitted development rights, which means no planning application is needed as long as you stay inside a fixed set of limits. These are national rules set out in the General Permitted Development Order, so Dorset Council and BCP Council apply the same measurements as everywhere else in England.
The core limits for a detached house are 4 metres of projection from the original rear wall, and 3 metres for a semi or terrace. Height is capped at 4 metres overall, and if the extension comes within 2 metres of a boundary the eaves cannot exceed 3 metres. Total footprint of all extensions and outbuildings must not cover more than half the land around the original house.
If you want to go deeper than the standard limits, the prior approval process (often called the neighbour consultation scheme) allows up to 6 metres on a semi or terrace and 8 metres on a detached house. You submit details to the council, neighbours get 21 days to comment, and if none object on grounds of amenity, approval is granted without a full planning application.
Fees are lower than a householder planning application and the determination period is typically around six weeks. It is worth talking to the neighbours yourself before submitting, because a single objection pushes the decision into an officer assessment and can add weeks to your programme.
This is where local geography bites. Permitted development is restricted or removed entirely in conservation areas, and BCP has a number of them, including Poole Old Town, Branksome Park, Canford Cliffs and Lilliput. Side extensions and cladding are the first things to go. Much of rural and coastal Dorset also sits within the National Landscape (formerly AONB) or the Purbeck and Cranborne Chase designations, which carry their own tighter limits.
Listed buildings always require listed building consent regardless of size. New estates around Poole, Upton and Wimborne frequently carry Article 4 directions or planning conditions from the original approval that strip out permitted development rights, so check your title deeds and the original estate planning decision. If you are near heathland in the Poole Basin, extensions creating additional bedrooms can trigger Heathland Infrastructure Project contributions, though pure extensions without extra dwellings are usually exempt.
Planning permission and building control are separate systems, and an extension that needs no planning permission still needs building regulations approval. That covers foundations, damp proofing, insulation values, structural openings, drainage and, increasingly, ventilation and overheating.
In Poole and much of the harbour fringe you should also budget for ground conditions. Made ground, high water tables and shrinkable soils near mature trees can push foundations from a standard 900mm trench fill to 1.5 metres or deeper, and that changes the cost materially. A trial hole before you price the job removes most of that uncertainty.
If you are building near or on a boundary, the Party Wall etc. Act 1996 also applies, and notice periods of one or two months need to sit in your programme rather than surprise you the week before the digger arrives.
The application fee is currently around £145 for a proposed use, plus drawings. It is not compulsory, but it is strong evidence for a future buyer's solicitor that your extension was lawful, and most surveyors we deal with will ask for it.
A householder application to BCP Council has a statutory eight week determination period, though validation delays can add a couple of weeks at busy times. Budget three to four months from first drawing to being ready to start on site.
Yes, in most cases, but the eaves height must stay under 3 metres if you are within 2 metres of the boundary, and you will need to serve Party Wall notice. You also cannot oversail the boundary with guttering or foundations without their agreement.
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