Area guide · WD7
House Extensions in Radlett (WD7)
Planning a house extension in Radlett? We design, gain planning permission and build substantial extensions in one of Hertfordshire's most affluent towns, where local agent guides put the average sale around £893,000 and the best streets trade past £4 million. Radlett briefs come in two sizes: the sensible family extension, and the serious programme, a double-storey rework, whole-house remodel or basement, which is the scale these plots were made for. Applications here go to Hertsmere Borough Council, with the green belt drawn tight around the town, and both of those facts shape the winning design before a line is drawn.
Live planning data
What Hertsmere Council is actually approving right now
Radlett sits within Hertsmere Borough Council, and the borough's approvals pipeline is healthy. In the latest Hertsmere pull from the published planning register, 13 residential schemes cleared, led by single-storey rear extensions and loft conversions, with double-storey and side extensions and a garden building alongside. The everyday schemes are moving without drama.
Radlett work skews bigger than the borough's average brief. On the avenues west of Watling Street the conversation is usually a wide glazed rear across the back of a detached house, a double-storey addition, or a full remodel that reorganises the ground floor around a new garden wing. Hertsmere decides these on design quality and, on the town's edges, on the green belt proportion test. Composing that case is the heart of how we win consents here, and it is why Radlett belongs in our luxury extensions cluster.
One Radlett-specific wrinkle worth knowing: the town lies within the historic parish of Aldenham, and the parish council is a consultee on planning applications. A well-prepared scheme gives the parish nothing to object to, which is exactly how we like to submit.
Source: the published planning register of Hertsmere Borough Council. The numbers describe the local approvals weather, not our own project list, and every application is decided on its own merits.
Local knowledge
Radlett's housing stock, avenue by avenue
Radlett is a long village-turned-town threaded along Watling Street, with its wealth spread through the avenues either side. Three broad generations of house set the playbook.
The west-side avenues. Along The Avenue, Loom Lane and Newlands Avenue, substantial detached homes sit on deep, hedged plots. This is prime territory for the large glazed rear (£55,000 to £115,000) and the wrap-around (£90,000 to £175,000): the gardens absorb serious footprints without the extension ever reading as cramped, and the street sees none of it.
The Edwardian and inter-war originals. Radlett grew with its railway, and the early houses near the station and along Gills Hill reward careful work: matched brick, proper joinery, roof junctions done the traditional way. These homes take a double-storey rear (£95,000 to £210,000) gracefully when the design respects their proportions.
The neo-Georgian rebuilds. Much of Radlett's newer stock is already generous, so the brief becomes reconfiguration plus extension: a kitchen-garden wing, a basement leisure floor, or a whole-house programme that makes a big footprint finally live like one. These are the flagship briefs banded honestly in our luxury extension cost guide.
The green belt edges. Towards Theobald Street and the town's fringes, plots run up against the Hertfordshire green belt. Extensions remain very possible; they must simply not be disproportionate against the original house. Our guide to extending in the green belt explains the test, and we calculate the headroom for your exact plot before design begins.
Every street is different. That's the point.
We design to Radlett'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 a house extension costs in Radlett in 2026
Radlett build costs run 20 to 30 percent above the North London baseline, reflecting plot sizes, specification expectations and the finish this market considers normal. Realistic all-in build ranges, excluding VAT, professional fees and kitchen fit-out:
| Extension type | Typical Radlett cost | On-site time | Usual planning route |
|---|---|---|---|
| Side-return extension | £45,000 to £85,000 | 2 to 3 months | Often permitted development |
| Single-storey rear | £55,000 to £115,000 | 3 to 4 months | Often permitted development |
| Kitchen extension (incl. mid-range kitchen) | £70,000 to £135,000 | 3 to 4 months | Often permitted development |
| Hip-to-gable loft + rear dormer | £65,000 to £115,000 | 6 to 10 weeks | Usually permitted development |
| Wrap-around extension | £90,000 to £175,000 | 4 to 6 months | Full application |
| Double-storey rear | £95,000 to £210,000 | 5 to 7 months | Full application |
| Garage conversion | £25,000 to £45,000 | 4 to 6 weeks | Usually permitted development |
Work to £3,300 to £5,200 per square metre against the wider baseline of £2,800 to £4,200. Our pricing method does not change with the postcode: a free design visit, then a fixed quote itemised line by line, and the figure you sign is the figure you pay.
Permissions, handled
Planning permission in Radlett: what you need to know
Hertsmere decides, Aldenham parish comments. Householder applications take roughly eight weeks to determine. We prepare the drawing set to Hertsmere's requirements and give the parish consultation nothing to push against.
Permitted development does the heavy lifting on many plots. A detached Radlett house can take a 4m single-storey rear without any application, or up to 8m through larger-home prior approval with neighbour consultation, and the loft allowance survives too. We secure a Lawful Development Certificate for everything built under PD so the position is documented when you sell.
The green belt applies at the edges, not the core. Central Radlett plots are usually unconstrained by it; the fringes are a different conversation, measured against the original building. We establish which side of that line your house sits on at the first visit.
Party walls. Detached plots keep formal awards rarer than in terraced streets, but boundary excavation, basements above all, can still trigger the Party Wall Act. Budget £1,000 to £2,500 per affected neighbour where surveyors are appointed. We serve and manage the notices as standard.
How it works
How it works
- Free design visit. We walk the plot, read the constraints, and talk honestly about feasibility, budget and the right planning route.
- Design and drawings. A set pitched at the standard Radlett expects, composed to answer Hertsmere's policies the first time.
- Planning, handled. Submission, parish consultation and officer questions managed end to end, through to the decision notice.
- Fixed-price build. Delivered by the team we trust with our name, signed off by building control, handed over immaculate.
Questions, answered
Radlett extension FAQs
Which council covers Radlett extensions?
Hertsmere Borough Council decides planning applications in Radlett, with Aldenham Parish Council consulted on schemes. A standard householder application takes around eight weeks to determine, and we manage the whole process including the parish dimension.
How much does an extension cost in Radlett?
Budget £3,300 to £5,200 per square metre in 2026. A glazed single-storey rear typically lands between £55,000 and £115,000, a double-storey rear between £95,000 and £210,000, and whole-house programmes, all excluding VAT and professional fees. Every project gets a fixed, itemised quote after a free visit.
Does the green belt stop me extending in Radlett?
Usually not. Most of central Radlett sits outside the green belt, and even edge plots can extend provided the addition is not disproportionate to the original house. We confirm your plot's position and remaining headroom before any design work.
Can I extend without planning permission in Radlett?
Often, yes. Detached houses carry 4m of rear extension under permitted development, extendable to 8m with prior approval, plus a generous loft allowance. We still obtain a Lawful Development Certificate so the consent is in writing.
Is a basement worth it in Radlett?
On the right plot, very much so. A basement adds leisure space no neighbour ever sees, keeps the house's street presence untouched and, at Radlett values, the space commands the investment. It is a full-application, engineering-led project and we price it on design.
How long does a Radlett project take?
A few weeks of survey and design, roughly eight weeks in planning, then three to four months on site for a single-storey scheme and up to seven for a double-storey rework. Programme dates come with the quote and we hold ourselves to 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
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