Where the planners measure from your neighbour's window
Every householder application in Birmingham gets tested against the 45 Degree Code. It now sits in the Birmingham Design Guide, adopted in September 2022, as City Note LW-4 in the Healthy Living and Working City Manual. Read it before you brief a designer.
The planner finds the nearest main window to a habitable room in the house next door and draws an imaginary line at 45 degrees from it. For a single-storey extension the line starts at the middle of that window. Go up to two storeys and it starts at the quarter-point instead, nearer your side, so a two-storey addition can't reach as far back. The guide is blunt about the result: proposals that cross the line will not be supported.
There are a few openings. A side window usually doesn't count unless it's the main light to a living room. Two neighbours who apply and build together can be given some leeway. Even so, the manual warns that extensions to historic buildings that break the code are unlikely to get through.
Side extensions have their own numbers. The ground floor should step back at least 500mm from the front building line, and anything at first floor or above at least 1,000mm, with a roof that copies the house but sits lower. The reason is the gaps between semis. Fill them all at full height and a street of pairs becomes a terrace. Front extensions are refused unless they improve how the house looks.
Which extension suits which Birmingham house
How each one sits with the city's houses and rules, with a link to a longer guide.
Single-storey rear. Where most semis start. Outside a conservation area you can usually build 3 metres out from the original back wall of a semi or terrace, or 4 metres on a detached house, without an application. Prior approval stretches that to 6 or 8 metres, though the neighbours are asked first and work can't start until the council has had its say or 42 days pass.
Kitchen. The Edwardian terraces of Selly Park Avenues were built with small front gardens and larger ones at the back, so there's room to go out. Rooflights over the worktop bring in daylight without new windows facing next door.
Side return. Suited to a terrace with a back addition and a passage beside it. The manual asks for extra care on terraces because the houses are so close, so keep the wall height down on the boundary and serve a party wall notice.
Open plan. Taking out the old back wall means a steel beam and calculations for building control. In Birmingham that service is provided for the council by Acivico.
Two-storey. This is where the quarter-point rule and the 1,000mm step-back both bite. On a 1930s semi with a side drive it can work well, but expect a full application and a lower ridge than the main roof.
Wrap-around. The side part takes it out of permitted development, so it always needs planning. Keep the side section 500mm behind the front of the house and the L-shape usually reads as subordinate.
Ground-floor bedroom. A downstairs bedroom and shower room lets an older relative stay put. Measure the garden you'll have left: the city's guide looks for 70 square metres of private outdoor space for a family house of three bedrooms or more.
Home office. A small room off the back is easier to heat and wire than a cabin at the end of the garden.
Planning. In any of the 29 conservation areas a side extension, or a rear one of more than a single storey, needs permission, and so does cladding. In the Moseley Article 4 area, any new porch or extension does.
Cost and value. We don't print prices. Steelwork, foundations on mudstone or clay, and conservation-grade bricks to match a Moseley villa can each move a quote a long way. Ask three builders to look at the house.
Sutton Coldfield's Green Belt, the river valleys and the ground
Not every Birmingham address is suburban. Around Sutton Coldfield some houses sit in the Green Belt, and there City Note LW-17 caps growth. An extension may be allowed if it adds no more than 50% to the habitable floor area, or 200 square metres if that's greater. Anything built in the previous 20 years counts towards it, and so does a garage attached to the house or within 5 metres of it.
Water runs through the city in the Rea, the Cole and the Tame, with smaller brooks like the Bourn in Harborne and Hatchford Brook. After the June 2016 storms the council found homes flooded inside at Perry Beeches, Selly Park North and along the Bourn. If your house is in Flood Zone 2 or 3, the application needs a flood risk assessment. For a householder extension the Environment Agency's standing advice sets out what to include.
Underneath, the Birmingham Fault splits the city. North-west of it is sandstone, which gives the centre its higher ground. South-east of it is Mercia Mudstone, which the British Geological Survey says can shrink and swell with moisture in places, and the south-west has a lot of clayey till. Building control will look at the trench before the concrete goes in.
Porches in Moseley and consent in Edgbaston
Eleven of the 29 carry extra Article 4 controls. The Moseley advice guide is the plainest: planning permission is needed for any new porch or extension, built in materials and a design that match the original house. On parts of Chantry Road and Salisbury Road that back onto the park, that reaches the rear elevations seen from the open space too.
On the Calthorpe Estate in Edgbaston there's a private layer as well. The residents' handbook says every extension and external alteration must be approved under the estate's scheme of management, whatever the council decides. Planning Online shows what was allowed next door, back to 1948.
Where these facts come from
- Birmingham Design Guide: Healthy Living and Working City Manual (2022)
- Birmingham City Council: Birmingham Design Guide
- Birmingham City Council: Moseley Article 4(2) advice guide
- Birmingham City Council: Article 4 directions in conservation areas
- Birmingham City Council: Strategic Flood Risk Assessment (2023)
- Birmingham City Council: flood investigation, June 2016
- British Geological Survey: Mercia Mudstone Group
- British Geological Survey: geology of the Birmingham area
- Calthorpe Residents' Society: residents' handbook
- GOV.UK: householder permitted development technical guidance
- Environment Agency: flood risk standing advice
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Questions people in Birmingham ask
My neighbour's only window near my wall is a side window. Does the 45 degree line still count?
Usually not. Birmingham's code measures from the nearest main window to a habitable room, and side windows are normally left out unless they're the main source of light to a living space. The planning officer decides which window counts.
We live in the Green Belt near Sutton Coldfield. How big can we go?
City Note LW-17 allows extensions that add up to 50% of the habitable floor area, or 200 square metres if that's larger. Earlier extensions from the last 20 years count, and so does an attached garage or one within 5 metres.
Can I build a porch in Moseley without applying?
Not if your house is covered by the Moseley Article 4 direction. The council's guide says any new porch or extension needs planning permission there, unless the house has been split into flats.