House Extensions Stanmore
Single storey rear and double storey extensions in Stanmore, 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
GS Renovation plans and builds extensions on Stanmore's houses, the substantial post-war and 1930s detached and semi-detached homes that sit on the generous plots typical of HA7. We have taken projects from foundations through steelwork to a finished, fitted-out space that suits the character of the area.
In Stanmore, 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 Stanmore: 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 Stanmore
Stanmore range: choose above
Rear, side and wrap-around extensions in Stanmore
The wide plots around Stanmore lend themselves to rear and side extensions, and often a wrap-around that combines both to create a large open living and dining space. Because these houses were built with a defined internal layout, opening up the rear usually means a steel beam sized by a structural engineer and signed off by building control. We handle the foundations and groundworks first, then the superstructure, the roof and the glazing that brings light deep into the plan.
Double storey extensions are also common on Stanmore's larger semis and detached homes, adding a bedroom or en-suite above the new ground floor room. We match brickwork and rooflines to the existing house so the addition reads as part of the original rather than a bolt-on. Every extension is built to current building regulations, with insulation, drainage and structural details all inspected and approved as the work progresses.
Housing in Stanmore
The stock in Stanmore runs to roughly 6,860 dwellings, 45% of them flats and 55% houses, built 4% before 1919, 21% between 1919 and 1939 and 75% after 1945. A detached house in Stanmore often extends far enough from the boundary that no party wall notice is needed, and 22% of homes here are detached.
Prior approval depths and the levy on bigger Stanmore extensions
39% of homes in Stanmore are semi-detached or detached houses, and for those, as for terraces, the prior approval route allows a deep single-storey rear extension without a full planning application. Harrow has 30 conservation areas, and on a house inside one the larger extension route is not available, so the extra depth has to come through a planning application instead. Harrow's prior approval page says the larger householder extension limit rises from 3 metres to 6 metres for terraced or semi-detached houses, and to 8 metres for a detached house. The depth you pick decides more than the room. A deeper footprint reaches further towards drains, trees and the neighbour's windows, so measure those on the plot before the architect draws the maximum.
Size also has a levy attached. Harrow's own CIL applies borough-wide where there is over 100 square metre gross internal floor space, and a large wrap-around on a Stanmore house can cross that line. Harrow's CIL page lists Form 9, the Residential Extension Exemption Claim, for a development that is an extension to a dwelling house. The claim is made before work starts, so it sits on the checklist beside the planning decision and the party wall notices, not after the footings are dug. Missing it is an avoidable liability on an extension that should have been exempt.
Planning and permitted development in HA7
Not every extension needs a full planning application. Many single storey rear extensions on Stanmore houses fall under permitted development, provided they stay within the limits on depth, height and materials, and that remains true in a conservation area unless an Article 4 direction applies. A conservation area does remove permitted development for side and two-storey extensions, and flats have none. Others, particularly larger, double storey or wrap-around schemes, do need planning permission from Harrow Council. We assess your specific property and tell you which route applies before you commit, so there are no surprises once the design is agreed.
Permitted development still requires building regulations approval, and the two things are separate. The drawings come from your architect or designer, whom we coordinate, and go to Harrow Council where planning is needed, while we manage the building control inspections throughout. Where the extension sits close to or on the party wall shared with a neighbouring Stanmore home, you serve the party wall notices as building owner; we give you the drawings and programme they need and build to any award. One team carries the project from first sketch to the final decorated, fitted-out room.
Kitchen extensions in Stanmore
71% of the houses in Stanmore 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 Stanmore; the build figures are in the table above.
Side return extensions in Stanmore
Side returns belong to Victorian and Edwardian terraces, and only 4% of homes in Stanmore 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.
Double storey extensions in Stanmore
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Stanmore often needs planning permission from Harrow Council. With 39% of homes here semi-detached or detached, the side of the house is often an option too. An Article 4 direction in Stanmore Hill Conservation Area, Stanmore, came into force on 20th June 2023 for Applegarth, The Glade and the Orchard in Green Lane (council source). Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Building control inspections at foundation, damp course and steel stages
- Drawings and the structural engineer's design coordinated for you
- Trial holes to set foundation depth near drains and trees
VOA Council Tax stock of properties, March 2025, for Stanmore Park and Stanmore Uxbridge Road. Counts rounded by the VOA.
Trusted House Extensions in Stanmore
Stanmore homeowners choose GS Renovation because we manage the whole extension under one roof, from the engineer's steel to the plaster finish. We tell you honestly whether your scheme is permitted development or needs a Harrow Council application, plan around the party wall notices you serve and keep every stage within building regulations. With our founder's 30+ years on the tools, we build additions that last.
- One point of contact from first survey to handover
- Weathertight shell reached before the fit-out begins
- Brick and mortar matched to the existing elevation
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 Stanmore
What happens to the house extensions price if the scope changes in Stanmore?
The house extensions price in Stanmore moves visibly when the scope changes, because the quotation is itemised within £2,000 to £2,800 per m² for a rear extension (indicative). A change at HA7 is priced against the same lines rather than renegotiated, and any change touching the approvals, such as permitted development or a planning application to Harrow Council, is flagged. GS Renovation issues a written variation and waits for approval.
What extension suits a detached Stanmore house?
Frequently a rear extension combined with the side space, because both are usually available. A detached property around Stanmore often has room to each boundary as well as a reasonable garden, which allows a wider footprint than a terrace ever could. That freedom makes daylight to the existing rooms the main design question rather than the plot. A wide shallow extension often works better than a deep narrow one.
Can a Stanmore garage be incorporated into an extension?
Often, and the existing garage structure is rarely adequate on its own. A garage at your Stanmore property was usually built with shallower foundations, a thinner wall construction and no insulation, so incorporating it means upgrading or rebuilding rather than simply fitting it out. The floor level frequently differs from the house as well. The engineer establishes what can be retained before the design assumes it.
What roof works over a wide Stanmore extension?
The one that lets daylight reach the middle of the plan. A wide extension at your Stanmore property creates a deep floor with its centre far from any window, so a flat roof with rooflights, or a pitched roof with glazing at the ridge, is what stops the middle going dark. The roof form is chosen for daylight and head height as much as for how it looks outside.
Where does surface water go from a Stanmore extension?
To a soakaway or a surface water drain sized for the additional roof area. At a Stanmore property with a garden, a soakaway is often the practical answer, positioned far enough from the building that it does not saturate the new foundations and tested for how quickly the ground accepts water. Connecting extension rainwater into a foul drain is not permitted.
How does Harrow's building control fee change with the size of a Stanmore extension?
It is banded by floor area. Harrow's Table B gives one total charge, with inspection included, for an extension with floor over 10m2 but not exceeding 40m2, and that charge is the same by full plans or building notice. Between 40m2 and 60m2 the charge on full plans is split into a plan charge and an inspection charge, while by building notice the same total is paid as one charge. Measuring the internal floor area accurately at design stage tells you which band applies.
Does a Stanmore extension in a conservation area bring extra rules for the driveway and boundary?
It can. Harrow's Conservation Areas Residential Planning Guidelines say Article 4 Directions can mean planning permission is needed to replace doors and windows, for any hardsurfacing, and for boundary walls and fences. An extension often finishes with a new drive, a rebuilt front wall or new patio doors, and each of those may be controlled. Check the direction for your street before the landscaping and the doors are priced into the job.
How long does Harrow's prior approval take for a deeper Stanmore rear extension?
Allow for the full period. Harrow's prior approval process for a larger householder extension includes consulting immediate neighbours and can last 42 days. Adjoining neighbours are told and can object, and the start date cannot be fixed until the decision is back. We use that time for the structural engineer's design and the building regulations submission, so the first dig can follow the decision rather than begin the paperwork.
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