Area guide · SL9
House Extensions in Gerrards Cross (SL9)
Weighing up a house extension in Gerrards Cross? The numbers set the scene: the average sale here runs at about £1.23 million, with detached homes averaging around £1.62 million (Rightmove sold-price data). SL9 is the stockbroker belt in its original form, 1930s mansions standing among tall pines, private roads where residents notice everything, and plots that were laid out for exactly the kind of project we build. Our sweet spot in Gerrards Cross is the substantial brief: double-storey reworks with full ground-floor remodels, basement leisure floors, whole-house programmes. Planning goes to Buckinghamshire Council, the green belt rings the town, and both are manageable with the case built correctly.
Live planning data
What Buckinghamshire Council is approving in SL9
Gerrards Cross applications land with Buckinghamshire Council, and the extensions that clear the desk without friction are the ones drawn for this town specifically: generous but composed, sympathetic to the pine-lined streetscape, and respectful of neighbour outlook on plots where houses sit well apart. Officers here read design maturity quickly, and a scheme that demonstrates it earns an easier ride.
Scale is normal in SL9, which changes the conversation in your favour. A wide glazed rear or a double-storey addition on a 1930s mansion is not an outlier; it is the local pattern. What we bring is the composition that lets a large addition read as inevitable rather than imposed, the discipline running through our whole luxury extensions service.
The green belt around the town is the constraint worth respecting early. Plots at the edges are tested on proportionality against the original house, so the first calculation on any fringe project is how much headroom the dwelling still holds. Our notes on extending in the green belt walk through the test in plain terms.
No council rubber-stamps anything; a complete, well-argued application is simply the strongest position you can occupy.
Local knowledge
The streets under the pines
Dukes Wood Avenue. One of the town's defining private roads: unadopted surface, substantial 1930s houses, residents with high expectations of anyone working there. We manage deliveries, protect the road and keep the site disciplined, because on a private road your builder's conduct is part of your reputation. The houses themselves take wrap-arounds (£102,000 to £192,000) and double-storey schemes with room to spare.
Camp Road. The same private-road character with plots that suit the biggest briefs: basement leisure floors, whole-house programmes and double-storey reworks (£105,000 to £230,000) that reorganise how the entire house lives.
Around Gerrards Cross Common. Facing the Common, family houses trade on their outlook, so the smart move is to build behind rather than beside: kitchen extensions (£75,000 to £150,000) and rear additions that leave the frontage exactly as the Common has always seen it.
The rebuilds among the pines. Plenty of SL9 stock has already been replaced with newer, larger houses. There the brief shifts to reconfiguration plus extension, taking volume that exists on paper and making it work as one coherent home, which is what our largest programmes really are.
Every street is different. That's the point.
We design to Gerrards Cross's stock and to what the council demonstrably approves — not to a template. A free site visit tells you what your house can take.
Get my free estimateHonest numbers
What an extension costs in Gerrards Cross in 2026
SL9 sits in our highest cost band. Build ranges below exclude VAT, professional fees and the kitchen units:
| Extension type | Typical Gerrards Cross cost | On-site time | Usual planning route |
|---|---|---|---|
| Side-return extension | £50,000 to £95,000 | 2 to 3 months | Often permitted development |
| Single-storey rear | £60,000 to £125,000 | 3 to 4 months | Often permitted development |
| Kitchen extension (incl. mid-range kitchen) | £75,000 to £150,000 | 3 to 4 months | Often permitted development |
| Hip-to-gable loft + rear dormer | £70,000 to £120,000 | 6 to 10 weeks | Usually permitted development |
| Wrap-around extension | £102,000 to £192,000 | 4 to 6 months | Full application |
| Double-storey rear | £105,000 to £230,000 | 5 to 7 months | Full application |
Sensible budgeting starts at £3,500 to £5,500 per square metre, and the luxury extension cost guide shows how the larger bands divide. None of this is an offer sheet: after a free design visit you get one fixed figure, itemised down to the ironmongery, and that is the figure we build to.
Permissions, handled
Planning permission in Gerrards Cross
Buckinghamshire decides, in roughly eight weeks. Allow around eight weeks for a householder decision once the application validates. We take it from first drawing to decision notice without handing you any of the admin.
Permitted development has real value on detached plots. The 4m rear allowance, the 8m prior-approval route and the loft rights all apply where they have not been stripped, and PD work leaves our office with a Lawful Development Certificate attached.
Private roads add logistics, not law. Unadopted surfaces on roads like Dukes Wood Avenue mean planned deliveries, road protection and considerate hours. We build that into the programme rather than discovering it in week one.
Green belt and party walls round out the list. Edge plots face the proportionality test, and boundary excavation can trigger the Party Wall Act; if surveyors are appointed the cost is £1,000 to £2,500 per affected boundary owner, with notices administered by us.
How it works
How it works
- Free design visit. Plot, pines, road access and budget, assessed honestly in a single appointment.
- Design to SL9's standard. A scheme composed for houses of this scale and for the neighbours who will watch it go up.
- Planning, done for you. Submission through to decision notice, with the green belt arithmetic handled where edge plots need it.
- Fixed-price delivery. An itemised figure signed before we mobilise, and a clean, respectful site kept throughout.
Questions, answered
Gerrards Cross extension FAQs
Who handles planning applications in Gerrards Cross?
Buckinghamshire Council is the authority for SL9, with householder decisions arriving in roughly eight weeks. We prepare, submit and manage the application in full, including any officer negotiation.
How much do extensions cost in SL9?
Work from £3,500 to £5,500 per square metre in 2026. A single-storey rear typically runs £60,000 to £125,000, a double-storey rework £105,000 to £230,000. Your own price is fixed and itemised after a free visit.
What about building on the private roads?
Entirely doable, with extra care. Unadopted roads mean we plan deliveries tightly, protect the surface and keep neighbours informed throughout. The planning process itself is unchanged; the site management simply has to be better.
Does the green belt affect SL9 plots?
Only at the fringes. Central Gerrards Cross is generally outside it, while edge plots must keep additions proportionate to the original dwelling. We establish which side of the line you sit on before designing anything.
Can I avoid a full application?
Sometimes. Detached houses retain useful permitted development allowances for rear extensions and lofts, and we document any PD build with a Lawful Development Certificate so the consent is beyond argument.
What timescale should I plan for?
A few weeks of design, roughly eight weeks in planning, then three to four months on site for single-storey work, stretching to seven months for a double-storey rework and longer for basements. Dates come with the quote and we hold them.
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What clients say
Rated 5.0 on Google
“Used The Extension Company for a loft conversion on our semi detached in Barnet and couldn't be happier. They explained what was possible at the first visit, sorted the planning side, and gave a fixed price with no surprises at the end.…” read the full review
“Really impressed with the entire project. The side extension and conservatory have been finished to a very high standard and the team made the process straight forward and stress-free. It’s transformed the space and added so much value, would definitely recommend.”
“Brilliant experience with the extension company, transparent from the word go. Completed a double story extension for me and I couldn’t be more pleased. Thank you”
“I got the extension company to do a bathroom refurb for us a January they done a great job they managed to fit in a large shower as well as a bath”
Reviews shown word for word from our Google profile. Read all 8 reviews on Google
Free site visit
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Free site visit anywhere in Gerrards Cross, honest feasibility advice and a fixed, itemised price — design, planning and build handled end to end by the Pine Grove team.
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