Can I do a 3 metre extension without planning permission?
Usually yes on a terraced or semi-detached house, provided it meets every other permitted development condition and the property is not a flat or in a conservation area. We would still recommend applying for a Lawful Development Certificate to prove it, which costs around £145 and protects you when you sell.
A 3m single-storey rear extension sits within permitted development for a terraced or semi-detached house. But 'within the depth limit' is not the same as 'permitted' — the height limit of 4m, the eaves height limit of 3m within 2m of a boundary, the materials condition, and the 50 percent curtilage rule all have to be satisfied too. A 3m extension with a 4.5m high roof lantern is not permitted development.
Even when you are confident, apply for a Lawful Development Certificate. It is not planning permission; it is the council confirming in writing that permission is not required. It costs about half a normal application fee, takes around eight weeks, and it is the document a buyer's solicitor will ask for. Without it you are relying on your own interpretation of the rules, and the burden of proof sits with you.
In Fulham the answer changes street by street. In a conservation area, permitted development rights for rear extensions may be restricted, and an Article 4 direction can remove them entirely. Because Hammersmith and Fulham has several designated areas, we always check the address rather than assuming — it takes minutes and it has stopped clients spending money on drawings for something that was never going to be permitted.
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