House Extensions Staines-upon-Thames
Single storey rear and double storey extensions in Staines-upon-Thames, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Guide from £40,000 (London-derived)
- Free site survey, itemised quote
An extension is a footprint, a set of dimensions the council expects you to work within, a foundation and a structure. We build it, coordinate the applications and the inspections, and appoint the structural engineer for the calculations. This page sets out the local rules, the flood position and the ground conditions that shape an extension in Staines-upon-Thames.
For Staines-upon-Thames, on London-derived ranges a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m²; Surrey work generally runs below that. GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Staines-upon-Thames: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Surrey work generally runs below the London figures; your price follows a site visit. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
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How deep a rear extension can go depends on the house type
Appendix C of the Spelthorne Design Code sets the depth by house type. It states that up to 4 metres on detached and semi-detached properties, and 3 metres on terraced properties, are usually acceptable subject to appropriate design and use of materials. Census 2021 recorded 415 households in detached houses in the Staines ward and 210 in the Staines South ward. Which depth figure applies to you follows the house type rather than the street.
Two further limits shape the back of the house. Two storey extensions with a footprint greater than 50 per cent of the original house are likely to require particular care in design and justification. The code also sets a minimum retained garden length of 10.5 metres in Inner Suburban and Suburban areas, rising to 15 metres for three storey development. It sets a minimum back to back distance of 21 metres, rising to 30 metres for three storey development.
Housing in Staines-upon-Thames
Staines-upon-Thames has around 10,840 homes on the Council Tax list: 68% post-war, 21% interwar and 10% predate 1919, with 37% flats and 63% houses. 27% of homes here are semi-detached; a rear extension on a semi in Staines-upon-Thames digs beside the attached neighbour, so one party wall notice is usual.
Side extensions have set in, set back and width rules to meet
The Spelthorne Design Code requires single storey side extensions to be set in from the plot boundary by at least 250mm, and set back from the main building line by at least 300mm. Appendix C explains that the set in allows for construction of foundations within the property boundary and avoids roofs, gutters and downpipes overhanging neighbouring properties. Subordinate multi storey side extensions must be set back from the main building line by a minimum of 1 metre.
Two more figures govern the shape. Side extensions should only exceptionally exceed two thirds of the width of the host building. Flat roofed extensions, and the height of pitched roofs nearest the property boundary, should not normally exceed 3 metres in height. The Design Code was adopted as a Supplementary Planning Document on 17 March 2026, so these are current requirements rather than draft guidance.
Flood risk decides floor levels and whether the footprint can grow at all
Spelthorne Borough Council's Strategic Flood Risk Assessment states that the section of Staines-upon-Thames which lies within the borough is almost entirely situated in a region of Flood Zone 2 and 3, medium to high probability. It gives the reason as the town's position on the banks of the River Thames. It states that of the four primary towns in Spelthorne, Staines-upon-Thames is that with the greatest risk from fluvial flooding. Surrey County Council is the Lead Local Flood Authority for the town under the Flood and Water Management Act.
Local Plan Policy E3 follows from that. Within Flood Zone 3b the footprint of a building should not be increased unless level for level floodplain compensatory storage can be provided. Finished floor levels shall not be lower than the existing and where possible should be raised, with a written justification required if raising is not possible. Sweeps Ditch matters on some plots. It heads at the junction of High Street and South Street, runs across Elmsleigh Car Park and under the railway, then passes behind Drakes Avenue and towards Knowle Green. The council maintains it as a land drain up to Laleham Road, at which point it is classed as main river.
An archaeological assessment can be required before the ground is opened
Approximately two thirds of the Staines Conservation Area is covered by an Area of High Archaeological Potential, so there is potential for the remains of earlier buildings and structures to survive beneath existing buildings and streets. Local Plan Policy PS3 requires an archaeological assessment with a planning application where development affects, or has the potential to affect, an Area of High Archaeological Potential, a County Site of Archaeological Importance or a Scheduled Monument. It applies the same requirement to all other sites over 0.4 hectares.
The council's appraisal records that the area was likely chosen as a Roman crossing point of the Thames because the subsoils are gravel rather than alluvial, providing solid foundations for bridge structures. Foundation depth for your extension is still decided by the engineer from a trial hole, not from a map. We dig one, record what is in it, and pass it on before the design is fixed.
Kitchen extensions in Staines-upon-Thames
57% of the houses in Staines-upon-Thames are semi-detached or detached, which usually leaves room for a kitchen extension across the full rear width, with a steel beam over the opening into the house. The fit-out is priced on its own page, kitchen renovation in Staines-upon-Thames; the build figures are in the table above.
Side return extensions in Staines-upon-Thames
Side returns belong to Victorian and Edwardian terraces, and only 10% of homes in Staines-upon-Thames predate 1919, so they are the exception here; most extensions run across the full rear width instead. Our side return extension page covers the build in detail, with build rates of £2,400 to £3,200 per m².
Double storey extensions in Staines-upon-Thames
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Staines-upon-Thames often needs planning permission from Spelthorne Borough Council. With 36% of homes here semi-detached or detached, the side of the house is often an option too. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Levels, drainage and landscaping made good around the new build
- First fix and second fix plumbing and electrics throughout
- Party wall process explained, and the extension built to the award
VOA Council Tax stock of properties, March 2025, for Staines Town, Staines South East and Staines South West. Counts rounded by the VOA.
Trusted House Extensions in Staines-upon-Thames
An extension in Staines-upon-Thames is constrained before it is designed, and that is the useful part to know early. Depth, set backs, roof height, garden length and back to back distance come from the Design Code. Floor levels, footprint increase and compensatory storage come from Local Plan Policy E3 and the flood position of the address. We check all of it at the survey, so the drawing starts from what is achievable rather than being cut back after a refusal. We then appoint the structural engineer, build to the calculations issued, make the building control application and coordinate the inspections. GS Renovation Ltd is fully insured, registered in England, company number 14611254, and quotations are free and without obligation.
- Garden levels and access made good where the build meets outside
- Dust screens and floor protection in occupied homes
- Brick and mortar matched to the existing elevation
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
The kitchen has been fitted to the high standard. Saaid was polite, professional, tidy, he pays attention to a little details that make huge…
Saiid did a complete refurbishment of our small bathroom. This involved ripping out the existing bath/shower, basin, toilet, pipework, and tiles and…
FAQ
Frequently Asked Questions about House Extensions Staines-upon-Thames
Can you quote house extensions for a TW18 property over the phone?
GS Renovation will not give a real quotation for house extensions in Staines-upon-Thames over the phone, only the range, £2,000 to £2,800 per m² for a rear extension (London-derived). On 07472 424 226 we can explain what moves the cost and whether the job needs permitted development or a planning application to Spelthorne Borough Council, but the TW18 property has to be seen first. Builders who quote blind across Staines-upon-Thames revise the figure once the floor or walls are opened.
The plot is in Flood Zone 1 but the surrounding streets are Zone 3. Which applies?
The surrounding zone applies. The Strategic Flood Risk Assessment records several small pockets of Flood Zone 1 land dispersed through the higher risk area in Staines-upon-Thames, which can become dry islands during certain flood events. The Local Plan states that dry islands should be treated the same as the level of flood risk in the area surrounding them, regardless of their size. So the extension is designed to the surrounding zone, not to the pocket.
Where does rainwater from a new extension roof go?
To a soakaway, in the pattern the borough's own drainage note describes. That note records that disposal of roof drainage has always been by means of soakaways, the exception being properties built close to or abutting the highway, where downpipes discharge onto footways or carriageways. Whether a soakaway performs depends on what sits under the garden, and British Geological Survey mapping shows London Clay Formation as the bedrock across the town. We dig a percolation pit before designing it.
Can a neighbour's window stop a two storey extension?
It can, through the 45 degree test. The Spelthorne Design Code requires two storey extensions to be clear of a 45 degree line drawn from the centre of a habitable room in a neighbouring property, both horizontally and vertically. Appendix C sets the horizontal guide as a clear area within a 45 degree arc from the centre of the face of the main window to that room. We plot it from the survey before any design work starts.
How far from the boundary does a two storey side extension have to sit?
At least 1 metre in from the plot boundary under the Spelthorne Design Code, rising to 2 metres for three storey development, or more to suit the context. That figure is separate from the set back along the main building line, which is a minimum of 1 metre for a subordinate multi storey side extension. Appendix C accepts a shorter set back only where the lesser distance is clearly justified in the information supporting your application.
Does a porch or conservatory have to prove no increase in surface water run off?
No. Local Plan Policy E3 requires development proposals to demonstrate no increase in surface water run off, and it excludes minor householder development such as porches and conservatories from that requirement. A larger extension is not excluded, so the surface water position forms part of the application. Surrey County Council is the Lead Local Flood Authority for the town, and the question it cares about is where the water goes once new roof and hard surfacing are added.
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