One metre back, 21 metres apart
Cheltenham planners still work from a householder guide adopted in February 2008, the Residential Alterations and Extensions document. It's old, but it is listed as current and officers quote it in their reports alongside the Cheltenham Plan's design and amenity policies. Read it before you brief anyone.
For a side extension on a semi, the guide expects the new front wall to sit at least one metre behind the original. It also wants clear space left to the side boundary. That second point is about the street. If both halves of neighbouring pairs fill their gaps at two storeys, a road of semis starts to look like a terrace, and the council says it may refuse where a neighbour's extension has already closed the gap. The roof should copy the house in pitch, shape and covering, and the extension shouldn't rise above the original.
At the back, there is no maximum depth. The guide treats 3 metres as the usual projection and warns that going further can leave rooms in the old part of the house dark and deep. Neighbours' light is checked against 45 degree and 25 degree principles. On privacy it gives real distances. Habitable room windows facing each other should be 21 metres apart, and a window should be 10.5 metres from the boundary it looks at. A conservatory's side wall should stand a metre off the boundary unless that end is solid.
What you can build without asking
Cheltenham has no Article 4 direction touching extensions. The only one, in St Paul's, controls shared houses. So on an ordinary house the national rules apply in full. A single-storey rear addition can go 3 metres deep (4 on a detached house) and 4 metres high with no application. The neighbour consultation route stretches that to 6 or 8 metres. A single-storey side extension can be up to half the width of the house. A two-storey rear one can go 3 metres back if it stays 7 metres from the rear boundary.
Inside any of the seven conservation areas, or in the slice of the borough that lies in the Cotswolds National Landscape, those rights shrink. No side extensions, nothing at the back over one storey, no cladding, and no 6 or 8 metre route. Listed houses need consent for any extension at all. The Montpellier appraisal adds that Regency backs are usually plain brick and the big villa gardens should be kept, so a rear addition there is judged on what it takes out of the garden as well as how it looks.
Clay, sand, brooks and roots
Most of the town sits on Lower Lias clay. The British Geological Survey says Lias clays shrink and swell because they contain smectite. On top, in places, is Cheltenham Sand and Gravel, which can be up to about 15 metres thick and varies a lot. Two houses in one road can need different footings. Dig trial holes before the engineer fixes the foundation design.
Trees make the clay worse, and Cheltenham has about 550 tree preservation orders on top of the protection trees get in conservation areas. Check the council's map before planning a footing near a mature tree.
The flood picture centres on the River Chelt, with past flooding on Wymans Brook, Prestbury Brook and Hatherley Brook too. If the house is in Flood Zone 2 or 3, an application needs a flood risk assessment. The Environment Agency suggests floors 600mm above the estimated flood level, or flood resistant materials to that height.
Which addition suits which house
Side return. Suits the Victorian terraces. St Paul's is a character area within the Central Conservation Area, and filling a side passage counts as a side extension, so there it means an application.
Single-storey rear. The easiest win on a postwar house in Hesters Way or Warden Hill. Keep within 3 metres and the 2008 guide and the national rules agree.
Two-storey. Mind the one metre set-back and the side gap. On the Poets estate the even spacing of the pairs is part of what the conservation area protects.
Wrap-around. Part side, part rear, so the side portion follows the semi rules above. In a conservation area it is a planning application from the start.
Kitchen. Interwar semis in St Mark's have long rear plots, so there is room to go out without crowding the garden. Watch the 45 degree line from the neighbour's back window.
Open plan. Regency backs are usually exposed brick, whatever the stucco front. Opening it up needs a designed beam, and on a listed house consent for the knock-through itself.
Home office. Attached space shares the house's heating and wiring. In a conservation area a garden building can't sit beside the house without permission either.
Ground-floor bedroom. Bungalows in Warden Hill suit this well. Near a brook, raise the new floor to sit above the estimated flood level.
Planning. First check the house against the conservation area and tree preservation order map. That tells you which set of rules you are under.
Cost. We don't publish a Cheltenham figure. Clay footings, flood levels and conservation drawings all move the price. Three quotes will show you by how much.
Where these facts come from
- Cheltenham Borough Council: Residential Alterations and Extensions SPD (2008)
- Cheltenham Borough Council: supplementary planning documents
- Permitted development rights for householders, technical guidance (GOV.UK)
- Cheltenham Borough Council: Article 4 directions
- Cheltenham Borough Council: Montpellier character appraisal
- Cheltenham Borough Council: protected trees
- Cheltenham Level 1 Strategic Flood Risk Assessment (2008)
- BGS: Lias Group engineering geology
- Flood risk assessment: standing advice (GOV.UK)
- Cheltenham Borough Council: Cotswold Beechwoods SAC
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Questions people in Cheltenham ask
The other half of our semi already has a two-storey side extension. Can we do the same?
Not automatically. The council's guide says it may refuse a side extension where the neighbour's has already used up the gap between houses, because the pair would read as a terrace. A single-storey version or one set well back is a safer pitch.
We have a big tree near where the extension would go. Does that matter?
Twice over. On Lias clay, roots drawing water out of the ground make it shrink, so the engineer may want deeper footings. And if the tree has a preservation order, or the house is in a conservation area, you need to tell the council or apply before touching it.
Our house is in the Green Belt on the edge of town. Is there a size limit?
There is no set percentage for extensions now. The old local plan policy was deleted when the Joint Core Strategy came in, so national policy applies. An extension mustn't be disproportionate to the house as it stood in July 1948, or as first built if later.
Do we pay the Cotswold Beechwoods contribution on an extension?
The council asks for it on additional dwellings, and its page says nothing about extensions. If you are planning a self-contained annexe, ask the case officer.