House Extensions Slough
Single storey rear and double storey extensions in Slough, 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 in Slough is judged against a specific document with specific numbers in it. Depth, height, roof form, the gap to a side boundary and the garden you have to keep are all written down. Slough Borough Council adopted its Residential Extensions Guidelines Supplementary Planning Document in January 2010, and it remains the document your design is judged against. We appoint the structural engineer, build to the calculations, and coordinate the building control application and inspections. Here are the numbers, before you commission drawings.
For Slough, on London-derived ranges a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m²; Berkshire work generally runs below that. GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Slough: 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. Berkshire work generally runs below the London figures; your price follows a site visit. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Slough
Slough range: choose above
The depths Slough works to at the back of a house
Slough's guideline maximum depth for a single storey rear extension is 3.65 metres for a terraced house and 4.25 metres for a semi-detached or detached house, measured from the rear main wall of the original house. For a two storey rear extension the guideline is 3.3 metres, with deeper allowed only where site circumstances permit, such as a detached house on a larger plot well separated from neighbours.
Height is written down as well. Where a single storey rear extension abuts a residential boundary, the guideline maximum is 3 metres for a flat roof, and 3 metres at the mid-point of the pitch at the side boundary for a pitched roof. All of it sits in the Residential Extensions Guidelines Supplementary Planning Document, adopted in January 2010.
Housing in Slough
The stock in Slough runs to roughly 57,360 dwellings, 37% of them flats and 63% houses, built 5% before 1919, 20% between 1919 and 1939 and 73% after 1945. A rear extension on a terrace in Slough digs foundations close to both neighbours, so notices to both are normal, and 34% of homes here are terraced.
First floor and two storey work, at the back and at the side
Slough Borough Council states that in general there is no potential for a first floor or two storey rear extension on a mid-terraced property. Its reasons are the adverse impact on adjacent properties, and that such extensions are generally out of keeping with the pattern of development. Where one is possible, Slough requires a pitched roof tied into the main roof of the house, and states that flat roofs will not be acceptable at that level.
Two further rules apply at that level. The council applies a 45 degree code on the horizontal plane, measured from the closest edge of the nearest first floor habitable window of the neighbouring property. It also expects a two storey or first floor side extension to be set off the side boundary by at least one metre, ideally at both ground and first floor level, to keep a visual gap between houses.
The garden you have to keep behind it
Slough will not permit a rear extension unless the usable retained rear garden keeps a minimum depth. That is 7 metres for a one bedroom house, 9 metres for a two or three bedroom house, and 15 metres for a house of four bedrooms or more. Where an irregular boundary means that depth cannot be reached, the council may relax the standard if the retained garden exceeds 40, 50 or 100 square metres on those same bedroom bands.
The reason is drainage as well as amenity. The council states that its minimum garden depths are set so that soakaways can be built for the correct disposal of surface water from approved extensions. It states that a soakaway needs to sit at least 5 metres from the completed extension. Measure the garden before you fix the depth, because the retained garden is what limits the extension rather than the other way round.
Permitted development in Slough, and how to be certain
The Article 4 direction we found published by Slough Borough Council covers the stationing of caravans and moveable structures across the whole borough, and it does not remove permitted development rights for house extensions. Directions can be added, so check the council's current Article 4 list for your address before relying on permitted development.
If you want certainty rather than a view, Slough Borough Council offers a Lawful Development Certificate where you want to be sure that your proposal is permitted development. It gives you the position in writing, which is worth having when the house is sold. We build to whichever route you take, and we tell you at survey which one your scheme is heading for.
Kitchen extensions in Slough
54% of the houses in Slough are terraced. On a terrace the kitchen extension is built out from the back, into the side return where the house has one or across the full rear width, and a steel beam takes the old back wall so the kitchen and the new room become one space. The fit-out is priced on its own page, kitchen renovation in Slough; the build figures are in the table above.
Side return extensions in Slough
Side returns belong to Victorian and Edwardian terraces, and only 5% of homes in Slough 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.
- Building control inspections at foundation, damp course and steel stages
- Levels, drainage and landscaping made good around the new build
- First fix and second fix plumbing and electrics throughout
VOA Council Tax stock of properties, March 2025, for all 15 statistical areas in Slough. Counts rounded by the VOA.
The GS Renovation Difference in Slough
Extensions in Slough succeed or fail at design stage, and the numbers are published. We take the depth, the height, the side boundary gap and the retained garden off your plot at survey, then set the design against the 2010 Residential Extensions Guidelines before drawings are commissioned. We appoint and coordinate the structural engineer, build to their calculations, and coordinate the building control application and inspections with Slough Borough Council. That is one point of contact from the first survey through to the final inspection. GS Renovation Ltd is fully insured and registered in England, company number 14611254, and rated 4.9 from 31 reviews on MyBuilder. Quotations are free and carry no obligation.
- Waste cleared as we go, not left piled up outside
- Foundation depth set after trial holes, drains and trees are checked
- Building control inspected at foundation, damp course and steel stages
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 Slough
How does your house extensions price in Slough compare with a national firm's?
National and local totals for house extensions in Slough are usually closer than the structures behind them, within £2,000 to £2,800 per m² for a rear extension (London-derived). A national firm subcontracts the work and prices its overhead into your quotation; GS Renovation carries out the SL1 job itself. Ask both for the same breakdown, and check that each prices the work in its proper order: the steel into the house is designed before the rear wall comes down.
How far forward can a front extension or porch go in Slough?
Slough's guideline maximum depth for a front extension, measured externally, is 2 metres for a detached house, 1.75 metres for a semi-detached house and 1.5 metres for a terraced house. Those figures sit in the same Residential Extensions Guidelines that govern the back of the house. A front addition is also the one seen from the street, so the building line and the materials carry weight in the assessment.
Does biodiversity net gain apply to a householder extension?
No. Slough Borough Council confirms that householders making planning applications are among the exemptions from biodiversity net gain. So the extension does not need a net gain plan or a habitat calculation with the application. That removes one document from the submission, though it changes neither the design tests the council applies, nor the separate building regulations application that the work still needs.
What is the ground like in Colnbrook, and does it change the foundation?
British Geological Survey 1:50 000 mapping shows Colnbrook village sitting on Alluvium, described as clay, silt, sand and gravel, over London Clay Formation bedrock. Alluvium is a variable deposit, so the founding depth on one plot is not evidence for the plot next door. That is a trial hole and a structural engineer's decision, taken before a price is fixed rather than after the trench is open.
Why is there so little room to expand in Slough?
The borough boundary is drawn tightly around the town. Slough's Core Strategy explains that this, combined with major physical constraints such as the M4 motorway, limits the borough's ability to expand, and that the lack of land means undeveloped areas such as Colnbrook and Poyle suffer overspill activity. Core Policy 1 then directs that development takes place within the built up area, predominantly on previously developed land.
How long does the council take to decide a householder application?
Slough Borough Council states that minor planning applications are determined within 8 weeks, major applications within 13 weeks, and applications with an environmental impact assessment within 16 weeks. A householder extension falls into the shortest of those categories. That period starts once the application is valid, so getting the drawings and certificates right first time is what protects the date. Building control runs on its own separate timetable.
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