Area guide · WD3 & SL9
House Extensions in Chorleywood & the Chalfonts (WD3 & SL9)
Considering a house extension in Chorleywood or the Chalfonts? This is Metroland's high ground: Arts and Crafts houses gathered around Chorleywood Common, the private roads of Loudwater, and beyond them the Chiltern beechwoods rolling into Buckinghamshire. It is also the trickiest consent geography on our patch, because Chorleywood answers to Three Rivers District Council while the Chalfonts fall to Buckinghamshire Council, and the first job on any project is confirming which desk your address reports to. The market is comfortably seven figures across the detached stock, and the commissions we relish most here are the substantial ones: double-storey reworks, leisure basements and whole-house programmes worthy of the setting.
Live planning data
Two councils, one route to approval
Nothing shapes a WD3 or SL9 project more than jurisdiction. Three Rivers District Council decides the Chorleywood side; Buckinghamshire Council takes the Chalfonts. Validation checklists, local policy wording and officer habits differ between the two, so we confirm the authority before anything is drawn and tailor the submission to the desk it will land on.
What both councils reward is the same thing: schemes that understand their setting. Around the Common that means Arts and Crafts language taken seriously, sweeping rooflines, brick and render handled with care, new work reading as a natural continuation. In the beechwood lanes it means designs that sit below the tree canopy and leave the leafy character intact. Composing extensions to that brief is the core of our luxury extensions service, and this corner of Metroland is where the method earns its keep.
Add one more layer on the Loudwater estate: private estate roads where covenants apply on top of planning consent. We treat covenant approval as part of the design brief, not an afterthought discovered at week ten.
Merits decide every case; our job is making sure yours arrives complete, to the correct council, first time.
Local knowledge
Housing stock from the Common to the Chalfonts
Around Chorleywood Common. The signature stock: Arts and Crafts houses with generous gardens facing the Common. New work succeeds when it defers to the original, so we run the ambition to the garden side, a wrap-around (£96,000 to £182,000) or a full-width glazed rear, and keep the street elevation untouched.
The Loudwater estate. Substantial houses on private estate roads with covenants in force. Extending here means clearing two gates, planning and covenant approval, and the natural briefs are the big ones: double-storey reworks (£100,000 to £214,000), basements and whole-house programmes designed to satisfy both.
Shire Lane and the county edge. Where Chorleywood runs out towards the Chalfonts, establishing which council you answer to is step one, and we do it before the tape measure comes out. The houses are large, the plots larger, and kitchen extensions (£75,000 to £145,000) with structural reworking behind them are the staple commission.
The beechwood fringes. Beyond the built edge sit the green belt and the Chilterns National Landscape, each bringing its own tests on scale and prominence. Extensions still happen here regularly; our guide to extending in the green belt covers how the proportion rules work and where the headroom hides.
Every street is different. That's the point.
We design to Chorleywood & the Chalfonts's stock and to what the council demonstrably approves — not to a template. A free site visit tells you what your house can take.
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What an extension costs in Chorleywood & the Chalfonts in 2026
This is the top end of our premium band. All-in construction ranges, before VAT, fees and kitchen fit-out:
| Extension type | Typical Chorleywood & Chalfonts cost | On-site time | Usual planning route |
|---|---|---|---|
| Side-return extension | £50,000 to £90,000 | 2 to 3 months | Often permitted development |
| Single-storey rear | £60,000 to £120,000 | 3 to 4 months | Often permitted development |
| Kitchen extension (incl. mid-range kitchen) | £75,000 to £145,000 | 3 to 4 months | Often permitted development |
| Hip-to-gable loft + rear dormer | £65,000 to £120,000 | 6 to 10 weeks | Usually permitted development |
| Wrap-around extension | £96,000 to £182,000 | 4 to 6 months | Full application |
| Double-storey rear | £100,000 to £214,000 | 5 to 7 months | Full application |
Budget towards the upper reaches of £3,200 to £5,000 per square metre, since Arts and Crafts detailing is never the cheap way to build. The luxury extension cost guide breaks down the larger bands. Ranges are indicative only: your project gets one fixed sum, itemised in full, after a free design visit.
Permissions, handled
Planning in WD3 and SL9
Address first, always. Council, covenants, green belt, National Landscape: the consent stack varies house by house, and we map yours completely before design begins.
Householder applications typically take about eight weeks to determine, whichever council decides. We prepare the pack to the relevant validation checklist so the clock starts without a hitch.
Permitted development survives on many plots. Where rights are intact, the standard rear and loft allowances apply, though covenants at Loudwater bind regardless of PD. A Lawful Development Certificate documents the position formally, and we secure one for all PD work.
Trees and boundaries need respect. Mature beeches shape siting decisions on the wooded lanes, and excavation near shared boundaries can invoke the Party Wall Act. Budget between £1,000 and £2,500 per neighbour where a surveyor is appointed, and leave the notices to us.
How it works
How it works
- Free design visit. The first question gets answered on the spot: which council, and whether covenants or designations apply.
- One design for every gate. Drawn to pass the council, the estate where relevant, and your own standards.
- Applications run in parallel. Planning and any covenant approval move together, so neither holds the other up.
- Build to a fixed sum. The itemised quote is agreed before work starts and holds to completion.
Questions, answered
Chorleywood & the Chalfonts extension FAQs
How do I know which council decides my extension?
It follows your address: Chorleywood sits under Three Rivers District Council, the Chalfonts under Buckinghamshire Council. We confirm jurisdiction at the free visit and shape the application to that authority's requirements from the outset.
What do the Loudwater covenants mean for my project?
On the estate, external alterations generally need approval under the covenants as well as planning permission. It is a design question more than a barrier: schemes composed for the estate's character clear both, and we run the approvals concurrently.
What will my extension cost here?
Expect the top of the £3,200 to £5,000 per square metre band in 2026. Single-storey rears commonly land between £60,000 and £120,000, double-storey schemes between £100,000 and £214,000. Everything is quoted as a single fixed, itemised figure.
Does the Chilterns designation rule out big schemes?
No, it raises the design bar rather than closing the door. On the fringes, both the National Landscape and the green belt ask that additions stay proportionate and visually quiet, which well-composed schemes achieve routinely.
Is permitted development still usable in WD3 and SL9?
Often, where rights have not been removed. Detached houses keep meaningful rear and loft allowances, covenanted estates excepted, and we put a Lawful Development Certificate behind every PD build.
How long does the whole process take?
Allow a few weeks for survey and design, roughly eight for the council decision with any covenant approval running alongside, then three to four months on site for single-storey work and up to seven for a double-storey rework.
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What clients say
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“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”
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Free site visit anywhere in Chorleywood & the Chalfonts, 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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