House Extensions Hayes
Single storey rear and double storey extensions in Hayes, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Single-storey rear extension from £40,000
- Free site survey, itemised quote
Extending a 1930s semi in Hayes is one of the most popular projects we take on. GS Renovation builds single and double storey extensions across UB3, and the generous interwar plots here often leave real room to the side and rear. We handle the groundworks, steel and fit-out from start to finish.
In Hayes, a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m² (indicative London ranges, Architecture for London, Resi, MyBuilder and Checkatrade, 2026). GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Hayes: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative London 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. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Hayes
Hayes range: choose above
Rear and side extensions in Hayes
The wide plots typical of Hayes suit side extensions and side infills, because many 1930s semis have a gap between the house and the boundary that can be built into. Whether you think of it as a room extension or a kitchen extension, a single storey rear addition opens the kitchen onto the garden, while a wrap-around scheme combines the side and rear to rework the whole ground floor. We dig and pour foundations to suit the ground, install any steel beams, then build up the walls, roof and openings.
Whether your extension is permitted development or needs a full planning application depends on the property, the size and how much has already been added. Many single storey rear extensions on these interwar plots fall under permitted development, but larger or two storey schemes, side extensions in a conservation area, and anything on a listed house may need permission from Hillingdon Council. We assess your home first, advise on the route, and work with the designer who prepares the drawings and applications.
Housing in Hayes
Hayes's housing, as the Council Tax list records it, is about 16,650 homes: 58% houses, 42% flats, with 4% pre-1919, 44% interwar and 52% built since 1945. A rear extension on a semi in Hayes digs beside the attached neighbour, so one party wall notice is usual, and 30% of homes here are semi-detached.
Measuring a Hayes rear extension from the original wall
Hillingdon's Article 4 Direction removes permitted development rights for residential extensions that extend beyond the rear wall of the original dwelling by more than 4 metres. It applies to the whole borough and came into force on 22 September 2014, so no part of Hayes is exempt. The ordinary allowance for a single storey rear extension is 3 metres on a semi or terrace and 4 metres on a detached house, and the Direction stops the larger prior approval route going past 4 metres. A 1930s semi in Hayes may already carry a later lean-to or kitchen addition, and the depth is measured from the original house, not from the back of whatever was added since.
Find the original rear wall before a design is fixed. For a house older than the modern planning system, original means the house as it stood when that system began after the war, so a very early addition can count as part of it. Old plans, a change in brickwork or a step in the floor usually show the line. If the new scheme sits close to the limit, Hillingdon's fast-track service determines householder lawful development certificate applications within 21 days of receiving the fast-track fee. That is worth having before steel and windows are ordered, because the certificate protects the extension when the house is sold.
Double storey extensions for Hayes families
Growing families in UB3 often want more than an extra room downstairs, so we build two storey side and rear extensions that add a bedroom or en-suite above a larger kitchen. On a 1930s semi this means matching the existing brick and roofline, tying the new structure into the old, and upgrading foundations where the extra load demands it. Building regulations cover the structure, insulation, drainage and fire safety throughout the works.
Because a second storey usually shares or sits close to the party wall with the neighbouring semi, these projects generally need Party Wall Act notices, which you serve early to keep things moving. We coordinate the structural engineer, the groundworks and the roof, then complete the full fit-out including plastering, electrics, heating and decoration. You deal with one team from the first survey to the final inspection by Hillingdon Council building control.
Kitchen extensions in Hayes
55% of the houses in Hayes 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 Hayes; the build figures are in the table above.
Side return extensions in Hayes
Side returns belong to Victorian and Edwardian terraces, and only 4% of homes in Hayes 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.
- First fix and second fix plumbing and electrics throughout
- Party wall process explained, and the extension built to the award
- Brickwork and mortar matched to the existing elevation
VOA Council Tax stock of properties, March 2025, for Hayes End, Hayes Town North, Hayes Town & Lake Farm and Hayes South. Counts rounded by the VOA.
The GS Renovation Difference in Hayes
Families in Hayes choose GS Renovation because we manage the whole extension under one roof, from the planning route with Hillingdon Council to the steelwork and the finish. Our founder's 30+ years on the tools mean we know how these interwar semis are built, so we tie new to old cleanly and keep the site tidy while you live in the house.
- Itemised pricing, so you can see what every stage costs
- Insulation and thermal detailing to current regulations
- Permitted development checked before you pay for a planning application
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 Hayes
Why do house extensions quotes in Hayes vary so much?
Variation in house extensions quotes across Hayes almost always comes from what has been left out. GS Renovation prices structure, trades, approvals and reinstatement after a UB3 survey, so the total can look higher than a quote covering half of it. The honest range is £2,000 to £2,800 per m² for a rear extension (indicative), and the width of the opening into the house decides the steel, which a quote without a survey cannot know.
Will my Hayes extension need planning permission or just building regulations?
It depends on the size and your property. Many single storey rear extensions on the generous Hayes plots are permitted development and only need building regulations approval, but larger, side or two storey schemes, or homes that have already been extended, may need a planning application to Hillingdon Council. We check your specific situation before anything is designed and build to whichever route applies.
Can I build into the side passage of my Hayes semi?
Frequently, since many 1930s semis in UB3 have a gap between house and boundary. A side infill usually runs along or near the boundary, so a party wall notice goes to the neighbour if you build on the line or dig near their foundations. Check the drains first: that passage often carries the house's main run, and building over it needs access and correct falls under Part H.
What foundations will my Hayes extension need?
Whatever the ground and nearby trees dictate. Hillingdon Council building control inspects the open trench before concrete is poured, and if the soil is soft or roots are present the depth can increase on the spot. Trees close to the footprint, including the neighbour's, matter most. Have the engineer and inspector agree the design before digging so a deeper pour is not a surprise.
Can I stay in my Hayes house while the extension is built?
Usually, because most of the build happens outside the existing walls. The shell is put up and made watertight first, and only then is the old rear wall opened with steel, so the house stays sealed for most of the job. The disruptive stretch is the knock-through week and the days the kitchen is disconnected, which can be planned around.
Rooflight or roof lantern on a Hayes extension: what changes?
A lantern sits proud of a flat roof and gives more light, but needs a larger opening, a trimmed roof structure and careful flashing. Flush rooflights are simpler. Either way Part L counts the glass towards the extension's heat loss, and generous glazing may need compensating insulation elsewhere. Fix the choice before the roof joists are ordered, as the opening is framed in.
Does the size of a Hayes extension change the building control charge?
Yes, it is banded by floor area. Hillingdon charges one total for a domestic extension of less than 40m2, whether by full plans or building notice, and a higher total for a domestic extension of 40m2 to 60m2. A wrap-around that combines a side infill with a rear addition can cross from one band into the next. Settle the footprint on the drawings before the application goes in, so the fee matches the scheme that is actually built.
Could a large Hayes extension be liable for the Community Infrastructure Levy?
Only at a size few house extensions reach. In Hillingdon the CIL applies to all proposals that add 100m2 of new floorspace or an extra dwelling. A two storey side and rear extension on a detached house can approach that figure, and a new dwelling in the garden triggers it regardless of size. An extension to your own home can usually claim relief from the levy, but the claim and a commencement notice have to reach Hillingdon before work starts, so check the floor area early.
When is Hillingdon's pre-application advice worth paying for on a Hayes extension?
When the scheme is complex or large. Hillingdon's Category F covers small scale minor proposals, including complex or large scale extension proposals, and carries a set fee including VAT. A two storey addition on a tight Hayes corner plot, or another scheme beyond permitted development, can fit that description. Hillingdon also says planning applications cannot be progressed until all the necessary supporting information and the appropriate fee are received, so pre-application feedback helps get the submission complete first time.
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