Birmingham is one of the largest planning authorities in England, deciding thousands of householder applications every year — and we get a steady stream of enquiries from homeowners here whose extensions have been refused. Like every council, Birmingham has a planning culture of its own, and one particular dislike stands out: deep single-storey rear extensions.
Birmingham has no fixed depth limit — which cuts both ways
Unlike many councils, Birmingham does not set a specific maximum depth for rear extensions. Plenty of authorities publish a hard 3m or 3.5m standard; Birmingham does not. In principle that is good news, because you can build to any depth provided you can justify it. The relevant policies sit in the Birmingham Development Plan, supported by the council’s ‘Extending Your Home’ guidance.
In practice, though, the absence of a fixed limit means the assessment turns almost entirely on one test — and that is where refusals come from.
The 45-degree rule and why it is a blunt instrument
Birmingham’s guidance recommends that rear extensions observe the 45-degree rule: an imaginary line drawn at 45 degrees from the midpoint of the neighbour’s nearest habitable window should not be crossed.
The difficulty is structural. Where houses are attached and in common alignment — which describes most of Birmingham’s suburban housing — almost any ground-floor rear extension breaches a 45-degree line. Even a 3m extension would, and those are usually permitted development requiring no application at all. Applied mechanically, the rule would prohibit extensions the government has already decided are acceptable without permission. That is a strong argument, and inspectors understand it.
What justifies a deeper extension
Our job is to show why greater depth is acceptable in your particular case. The arguments that work are specific rather than general: the height of the extension, its position relative to the boundary, the orientation of the two houses and where the sun actually falls, boundary treatments such as tall fencing or mature planting, differences in ground levels, which of the neighbour’s windows are affected and whether they serve principal rooms, and what neighbouring properties have already built.
We won permission at appeal for a 5m single-storey rear extension to a semi-detached house in the south of the city on exactly this basis, after the council refused prior approval for a larger home extension. Our success rate in Birmingham is high, and higher still for single-storey rear extensions.
If your refusal talks about the extension being overbearing or causing loss of light, those judgements can be tested on the evidence — and appeals are decided by independent inspectors with no connection to the council.
Appealing under the 2026 rules
Since April 2026, householder appeals are decided on your original application documents plus a concise 250-word summary — nothing can be added later. That makes the drawings crucial in Birmingham cases: sun paths, levels, boundary treatments and window positions need to be shown from the outset. See our complete guide to winning a planning appeal. You have 12 weeks from the date on the decision notice.
Refused planning permission in Birmingham? Send us your refusal for free initial advice — we’ll tell you honestly whether an appeal is worth pursuing, and if it is, we handle everything for a fixed fee of £399.