A 45 degree line and 21 metres of privacy
County Durham judges house additions against one document, the Residential Amenity Standards supplementary planning document. First adopted in January 2020, it was refreshed after a 2022 consultation. Read the current version before briefing a designer.
The test officers reach for first is the 45 degree code. Take the nearest habitable room window next door, find its middle point and draw a line out at 45 degrees. If your plan crosses it, expect questions. The council calls it a guide, not a rigid standard, and its updated wording treats a breach as a trigger for a daylight check rather than an automatic refusal.
Then come the distances. Main windows of habitable rooms in two storey houses should be 21 metres apart, or 18 between bungalows. A main window facing a blank two storey gable needs 13 metres, and a single storey gable 10. Add 3 metres for every extra storey. On a tight terrace in Framwellgate it can kill a first floor addition before the drawings are done. Back gardens should stay at least 9 metres long unless the site justifies less.
For the side of a house the council asks two things. The addition should stay no wider than half the original frontage, and anything with a first floor should ordinarily step back at least a metre from the front wall. That is aimed squarely at the semis on estates like Newton Hall, where filling the gap between pairs is the obvious move. A flat roofed, modern single storey addition at the back may be fine where the street can't see it.
Which addition suits which Durham house
Roughly in order of demand. Each links to a fuller guide.
Single storey at the back. The council itself calls building at the rear the simplest route. Outside a conservation area a semi or terrace gets 3 metres under national permitted development, or up to 6 through prior approval, which neighbours are told about.
Kitchen. The usual brief on a Newton Hall semi. Where next door's kitchen window sits near the fence, the 45 degree line usually decides how deep you can go.
Two storey. Permitted development only covers it 7 metres or more from the back boundary, and never in a conservation area, so most need an application. Check the 21 metre window distance first. It rules out more schemes here than design does.
Wrap-around. Part of it counts as a side addition, which permitted development doesn't allow anywhere in the city conservation area. Outside it, on a corner plot or a detached house with room on two sides, a normal application often gets one through.
Side return. Fits the Victorian terraces with a rear offshoot and a narrow yard beside it. Most of the Crossgate and Gilesgate examples sit in the conservation area, which means an application.
Open plan. Taking out the back wall of a stone terrace means a steel beam and an engineer's calculations for building control. Sort those before you ask anyone to price it.
Downstairs bedroom. Easiest on a bungalow or a semi with a wide drive. Keep it single storey and the privacy distances rarely come into it.
Home office. Attached usually makes more sense on a city plot, because the 9 metre garden guideline leaves little room for a separate cabin as well.
Planning. Before hiring anyone, check the conservation area map, the flood map and the house's letting status. Building under permitted rights? Get a lawful development certificate.
Cost. No Durham figure from us. Ground is the big unknown here, so get the mining and flood checks done before you ask builders for numbers.
Riverside streets, old pits and boulder clay
The Wear loops right round the middle of Durham, and the Environment Agency runs four flood warning areas through it. They take in streets such as New Elvet, Old Elvet, Providence Row, Framwellgate Waterside, Wearside Drive, Green Lane and Frankland Lane, along with Elvet Bridge and High Street. If your plot is in Flood Zone 2 or 3, any planning application must come with a flood risk assessment, even for a small back kitchen.
Dig a trench almost anywhere in the lowlands of the county and you'll hit the Wear Till, which the British Geological Survey describes as an extremely compact, stony, sandy, silty clay. Below that sit the Coal Measures, and dozens of collieries once worked round the city. Check the government's coal mining map before the foundations are designed. In a development high risk area you need a Mining Remediation Authority permit if footings or new drains could reach old seams, workings or a shaft. If one turns up mid-dig, ring the Mining Remediation Authority's 24 hour hazard line.
Trees matter too. In a conservation area the council wants six weeks' notice before work on any tree with a stem over 75mm thick at 1.5 metres up, and trees under a preservation order need consent.
Student houses that grow at the back
Inner Durham has a long record of family houses turned into shared student lets, and a single storey addition at the rear is a common way to squeeze in more bedrooms. The 10% student concentration test in Policy 16 is for new HMOs, yet the plan Inspector kept some of its other criteria in play for work that adds bedspaces. Seven or more sharers makes a large HMO, and that change of use needs its own consent.
The City of Durham Neighbourhood Plan adds design policies of its own, including one aimed at additions to existing housing, On the 2016 Article 4 streets, such as Hawthorn Terrace, Albert Street and Nevilledale Terrace, even a front porch needs consent. For anything in the city, the first call is Durham County Council's own building control team.
Where these facts come from
- Durham County Council: Development Plan supporting documents (Residential Amenity Standards SPD)
- Durham County Council: Residential Amenity Standards SPD update consultation
- Durham County Council: Residential Amenity Standards SPD revised draft (2022)
- GOV.UK: Permitted development rights for householders, technical guidance
- Environment Agency: River Wear at Elvet and Framwellgate flood warning area
- Environment Agency: River Wear at Upper Durham flood warning area
- GOV.UK: flood risk assessments for planning applications
- Environment Agency: flood risk standing advice
- GOV.UK: home extensions in former coal mining areas
- BGS Lexicon: Wear Till Formation
- Durham County Council: protected trees
- Durham County Council: Durham City conservation area and Article 4
- Durham County Council: multiple occupancy homes
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Questions people in Durham ask
I'm in a semi on Newton Hall. How wide can a two storey side addition be?
The council's amenity guidance asks for no more than half the width of the original house, set back at least a metre from the front wall at first floor. It's a guideline, not a fixed cap, but designs that ignore it rarely do well.
My house is on Wearside Drive. Can I still add a kitchen at the back?
Often yes, but check the flood map for planning first. If the plot is in Flood Zone 2 or 3 and you need an application, include a flood risk assessment. The Environment Agency's standing advice for minor extensions tells you what to cover.
Can I extend the back of my Gilesgate terrace without applying?
Inside the conservation area a single storey rear addition can still be permitted development within the normal limits, though larger ones through prior approval can't be, and a listed house needs listed building consent. Side and two storey additions need permission there.
Will adding a bedroom to my student let in Elvet need permission?
The building work does if it goes beyond permitted rights. Separately, a seventh sharer turns the house into a large HMO, which needs consent however small the addition.