Area guide · HA7
House Extensions in Stanmore & Bushey Heath (HA7)
Planning a house extension in Stanmore or Bushey Heath? The wooded ridge between them is one of north-west London's quiet wealth pockets: substantial detached houses on tree-screened plots climbing from Stanmore towards the common, the 1930s modernist run of Kerry Avenue, and the Brockley Hill corridor where the houses turn into small estates. It is also a borough boundary: Stanmore answers to Harrow, Bushey Heath to Hertsmere, and which desk your application lands on changes the policies it is judged against. The briefs up here are big, double-storey reworks, basements and whole-house programmes, and reading the boundary correctly is step one of winning them.
Live planning data
What the two councils approve on the ridge
The boundary runs along the top of the hill, so near-identical houses a few hundred metres apart can answer to different rulebooks. Harrow decides the Stanmore side, Hertsmere the Bushey Heath side, and both are approving the staple schemes steadily; Hertsmere's latest published pull cleared a healthy sheet led by rear extensions and lofts, and Harrow's suburban approvals run to the same pattern.
What the ridge adds is designation reading. Parts of Stanmore carry conservation areas, the upper slopes meet green belt, and the tree cover is protected enough that siting often decides a scheme before style does. None of it prevents the big projects; all of it rewards the design-first preparation we bring to every luxury extensions job.
Sources: the published planning registers of Harrow and Hertsmere. Register patterns describe the approvals weather; every application turns on its own design.
Recent extension approvals near Stanmore & Bushey Heath
We tracked 2 residential extension and loft approvals in the HA7 area, most decided by Harrow Council. Most are single-storey rear extension, side extension. Here are some recent examples that secured approval — useful context for what tends to get through on Stanmore & Bushey Heath homes:
49 Beatty Road, Stanmore
Single storey rear extension: 5.45 metres deep, 3.01 metres maximum height and 3m metres high to the eaves.
HA7
3 Uppingham Avenue, Stanmore
Single storey side extension; single storey rear extension (demolition of conservatory).
HA7
Source: public local-authority planning decision records. Approvals shown are recent examples of schemes granted in the area to illustrate what is achievable locally — they are not necessarily projects undertaken by us. Planning outcomes depend on your specific property and proposal.
Local knowledge
The ridge's stock, road by road
The avenue detached belt. Along Gordon Avenue, Wood Lane and the roads under the hill, substantial inter-war detached houses on wide plots take the classic premium schemes: wide glazed rears (£55,000 to £120,000), wrap-arounds (£95,000 to £180,000) and double-storey reworks (£100,000 to £215,000) that read as original.
Kerry Avenue and the modernist pocket. Stanmore's 1930s modernist houses are a design responsibility: flat roofs, white render, curved glass. Extending them demands their own language rather than a brick pastiche, and done properly the results are spectacular.
The common and the green edges. Towards Stanmore Common and Warren Lane, plots meet woodland and the green belt frame appears. Additions here are sited around root protection and long views, with the proportion arguments from our green belt guide doing the policy work.
Brockley Hill and Bushey Heath. The corridor towards Elstree is the top of this market: gated houses on deep plots where the brief is usually extension plus whole-house remodel, and where Hertsmere is the authority to design for.
Every street is different. That's the point.
We design to Stanmore & Bushey Heath'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 here in 2026
All-in build ranges, excluding VAT, professional fees and kitchen fit-out:
| Extension type | Typical 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 £120,000 | 3 to 4 months | Often permitted development |
| Kitchen extension (incl. mid-range kitchen) | £70,000 to £140,000 | 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 | £95,000 to £180,000 | 4 to 6 months | Full application |
| Double-storey rework | £100,000 to £215,000 | 5 to 7 months | Full application |
Budget £3,300 to £5,300 per square metre depending on side of the hill and specification. The the larger bands are set out in the luxury extension cost guide, and the quote is always one fixed, itemised figure after a free visit.
Permissions, handled
Planning on the boundary: what to know
Confirm the authority first. Harrow and Hertsmere differ in policy detail and process. We establish yours at the outset and prepare the file for that desk.
Permitted development mostly survives. Outside the conservation pockets, detached houses keep the 4m and prior-approval 8m rear allowances plus loft volume, and we certificate everything built that way with a Lawful Development Certificate.
Trees before floor plans. Protected woodland cover shapes siting on the upper roads. Root protection surveys come early in our process because they decide what the plot can actually take.
Party walls. Boundary excavation, basements included, triggers the Act as usual: budget £1,000 to £2,500 per affected neighbour where surveyors are appointed, notices managed by us.
How it works
How it works
- Free design visit. Authority confirmed, designations and trees mapped, honest advice on scope and budget.
- Design and drawings. Composed to the house's own language, modernist or traditional, and the policies it must satisfy.
- Planning, handled. The application managed through Harrow or Hertsmere to the decision notice.
- Fixed-price build. One signed figure, delivered by the team we trust with our name, handed over immaculate.
Questions, answered
Stanmore & Bushey Heath extension FAQs
Which council will decide my application?
Harrow for Stanmore addresses and Hertsmere for the Bushey Heath side. The boundary runs along the ridge, so we confirm your exact position first; it changes the policies, the forms and occasionally the tactics.
What does an extension cost up here?
Plan on £3,300 to £5,300 per square metre in 2026. Glazed rears typically run £55,000 to £120,000 and double-storey reworks £100,000 to £215,000, excluding VAT and fees, with the whole-house programmes banded in our luxury cost guide. Every quote is fixed and itemised.
Can you extend the modernist houses sympathetically?
Yes, and it is some of our favourite work: flat-roofed, rendered additions with crittall-style glazing that extend the original architecture rather than argue with it. Conservation designations on those streets make the design case decisive, which suits a design-led application.
Does the green belt affect me?
Only on the upper plots that meet it, where extensions are measured against the original building. We calculate that headroom at the first visit and design inside it.
Is a basement realistic on the ridge?
On the larger plots, often yes, subject to ground conditions we assess early. It adds a leisure floor without touching the tree screening or the street presence, priced on design as a full-application project.
How long will it all take?
A few weeks of design, roughly eight in planning, then three to seven months on site by scale. Programme dates come with the quote and we hold ourselves to them.
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
Ready to see what's possible on your street?
Free site visit anywhere in Stanmore & Bushey Heath, honest feasibility advice and a fixed, itemised price — design, planning and build handled end to end by the Pine Grove team.
020 3051 9430Lines answered weekdays 8am to 6pmEvery area we cover
Browse the full areas guide →Enfield & the EN heartland
Cockfosters · Oakwood · Southgate · Winchmore Hill · Palmers Green · Enfield · Edmonton
Barnet borough
Barnet · East Barnet · New Barnet · Hadley Wood · Arkley · Monken Hadley · Hampstead Garden Suburb · Whetstone · Totteridge · Finchley · East Finchley · North Finchley · Friern Barnet · Hendon · Golders Green · Mill Hill · Edgware
Hertfordshire border
Potters Bar · Radlett · Shenley · Elstree & Letchmore Heath · Northaw · Cuffley · Cheshunt · Waltham Cross · Brookmans Park · Hatfield · Hoddesdon
St Albans & the Chilterns
Harpenden · St Albans · Chorleywood & the Chalfonts · Gerrards Cross · Beaconsfield
Haringey & the N postcodes
Muswell Hill · Highgate · Crouch End · Hornsey · Wood Green · Tottenham
North-west London
Hampstead · Moor Park & Northwood · Stanmore & Bushey Heath
East & the Essex edge
Stoke Newington · Walthamstow · Chingford · Loughton · Chigwell · Theydon Bois & Epping · Hutton Mount & Shenfield
South-west London & Surrey
Richmond · Wimbledon Village · Esher · Oxshott · Cobham · St George's Hill · Wentworth & Virginia Water
South London & the Surrey downs
Chislehurst · Purley & the Webb Estate · Banstead · Kingswood & Walton-on-the-Hill