Twenty metres from the brook
Derby is threaded with water. Besides the Derwent there are half a dozen brooks, the Markeaton and Cuttle among them, and plenty of back gardens run down towards one. An extension puts new floor at ground level, so this is where a Derby project starts.
The council's validation list asks for a flood risk assessment with a householder application in Flood Zone 2 or 3, and also on any site within 20 metres of a watercourse. Miss it and the application is not treated as valid. The Core Strategy puts much of the Derwent valley, the Markeaton Brook system to the north west and parts of Sinfin Moor in Flood Zone 3.
Water can come up as well as over. The city's 2025 strategic flood risk assessment names Markeaton, New Zealand, Alvaston, Boulton, Crewton and Wilmorton as the places most at risk of groundwater emerging. Living there? Settle floor levels and the damp proof course with your designer before the drawings are fixed.
No Derby rulebook, so what do officers use?
Many councils publish a householder design guide with a 45 degree line and a maximum depth. We could not find one for Derby. Applications are weighed against the 2017 Core Strategy and the policies saved from the 2006 local plan.
The Core Strategy says its design principles apply to everything from "domestic extensions to multi-million pound developments". Policy CP4 compares scale, massing and materials with the neighbouring buildings, and proposals that don't fit "will be resisted". The older amenity policy, GD5, lists loss of sunlight and daylight among the things officers consider. So the test is judgement, not a number.
That judgement is stricter in what the plan calls areas of mature townscape character. They sit in and around the old villages and along historic routes into the centre, with older homes on bigger plots behind front walls and hedges. A flat roofed box on the side of an Edwardian house in one of those streets will get a harder look than the same box on a 1990s estate.
Matching the type to the house
In the order they tend to suit Derby homes. Each one links to a fuller guide.
Single storey at the back. The usual starting point on the suburban semis that make up the largest share of the city's housing. Under permitted development you can go 3 metres from the original rear wall, or 6 with prior approval, when the council consults the neighbours and has 42 days.
Kitchen. Often the reason for the whole job. Where a garden backs onto a brook, keep the new kitchen floor level with the house and think about where the drains will run before you choose the glazing.
Side return. Fits the Victorian terraces with a narrow yard beside the back wing, found in the older inner districts. In Hartington Street, Little Chester or any other conservation area, building out beyond the side wall needs a planning application.
Wrap-around. Good on a semi with a drive down one side. The side part is limited to half the width of the original house and 4 metres high, and in a conservation area the whole thing goes to the planners.
Open plan. Knocking through the old back wall needs a steel beam sized by an engineer. On a semi, find out early what sits above the wall you want to remove, because a chimney breast or a bedroom wall changes the steel.
Two storey. Permitted development only stretches to 3 metres deep and 7 metres clear of the back boundary, which shorter terraced gardens rarely allow. Most go in as applications, judged on scale, massing and materials under CP4.
Downstairs bedroom. Lets an older owner stay put. Inside a flood zone, ask for the bedroom floor to sit above the predicted flood level.
Home office. Attached means one heating system and one building control file. Where the garden runs down to a brook, the far end is also the wettest corner of the plot.
Planning. Derby Maps shows conservation areas, Article 4 layers and protected trees. Newer estates can have permitted development removed by a condition on the original consent, so search the planning register for your street before assuming anything.
Cost. We don't publish Derby prices. Foundations on mudstone or river gravels move a quote more than the kitchen does, so ask how each builder has allowed for them.
Village cores, the Green Belt edge and Darley Abbey
Every Derby conservation area counts as article 2(3) land. No side extensions, nothing over one storey at the rear and no cladding without an application, and the bigger rear extension through prior approval is off the table. So in Spondon, Allestree or Mickleover village, even a modest wrap-around is an application.
The Article 4 directions in ten of those areas are a separate layer. They bring doors, windows and roof coverings facing the road under control. A rear extension that changes nothing on the street side isn't caught by them, though the conservation area rules above still are.
Darley Abbey adds the Derwent Valley Mills World Heritage Site. An application there needs an assessment of the effect on the site's significance as well as the usual drawings.
Out on the edge, the Core Strategy describes Green Belt along the northern, eastern and south eastern fringes of the city. Derby sets no percentage cap that we found. National policy allows an extension to a house in the Green Belt only if it isn't disproportionate to the original building, and earlier additions count against you.
Sign-off comes from the Derbyshire Building Control Partnership or a private inspector. Keep the completion certificate with the deeds.
Where these facts come from
- GOV.UK: Permitted development rights for householders, technical guidance
- Derby City Council: Local List of Validation Requirements (October 2025)
- Derby City Council: planning constraints
- Derby City Local Plan Part 1: Core Strategy (adopted 2017)
- City of Derby Local Plan Review (saved policies)
- Derby City Strategic Flood Risk Assessment Level 1
- Derby City Council: Design Optimisation Service
- Derby City Council: pre-application advice for residents
- Derby City Council: conservation area FAQs (Article 4)
- NPPF: protecting Green Belt land
How FirQuote works in Derby: We connect you with local specialists who visit your property before giving you a price. You get up to 3 written quotes — no call centres, no estimates from photos, no obligation to accept any quote.
Questions people in Derby ask
Our garden backs onto the Markeaton Brook. Do we need a flood report for a kitchen extension?
For a planning application, almost certainly. Derby's validation list asks for one on any site in Flood Zone 2 or 3, and on any site within 20 metres of a watercourse. Under permitted development there is no application to attach it to, but the flood risk is the same.
Does Derby have a 45 degree rule for extensions?
We found no published Derby householder guide with one. Officers weigh light and outlook under the saved amenity policy GD5 and design under Core Strategy policy CP4. Within permitted development, no local test applies.
Can I get the council's opinion on a design before I apply?
Yes, for a fee. Residents can ask for pre-application advice, and the Design Optimisation Service runs a domestic workshop with written advice afterwards. Neither binds the eventual decision. To confirm something is permitted development, apply for a lawful development certificate instead.
We live in Spondon village. Can we add a single storey side extension without permission?
Not inside the Spondon conservation area. Side extensions are not permitted development on article 2(3) land, so it needs a planning application. A single storey rear extension within the 3 metre limit may still be allowed.