TL;DR — Key Facts
- Build cost per sqm: £2,500 – £3,800 (inner London borough)
- Council planning fee: £548 (householder application, 2026)
- Typical projects: rear extension, side-return, two-storey, wraparound
- Conservation areas: 22 designated areas in Brent
- Permitted Development: Restricted by Article 4 in some areas
What does Brent do with an extension application?
It refuses more of the 6m route than it grants: 27 prior approvals granted against 249 refusals, with 518 ruled not required. Brent approved 78.5% of householder applications overall and issued 399 enforcement notices, more than any other London borough.
| Brent, three years to March 2026 | Count | Share |
|---|---|---|
| Larger-extension notifications decided | 794 | — |
| Prior approval not required | 518 | 65.2% |
| Prior approval granted | 27 | 3.4% |
| Refused | 249 | 31.4% |
| Householder decisions | 2,843 | 78.5% approved |
| Enforcement notices issued | 399 | second highest in London |
| Extension applications in the Datahub | 12,772 | 69% approved |
Sources: decision and enforcement figures from MHCLG District Planning Application Statistics (PS1 and PS2), twelve quarters to March 2026; the Datahub row from the Planning London Datahub, retrieved 15 August 2026, phrase-matched and comparable within Brent only. Build costs on this page are our own 2026 London range, not a published statistic. A ‘not required’ ruling means the extension may be built as notified.
What does a Brent extension cost in 2026?
Costs here are build costs. For the drawing package itself — scope, fee and timeline — see house extensions in Brent.
House extension build costs in Brent typically range from £2,500 to £3,800 per square metre, reflecting Brent's position as an inner London borough. These figures cover the construction cost only and do not include professional fees, planning fees, or VAT.
The spread in Brent is driven by which half of the borough you are in. On a Wembley semi the cost is a conventional structural job. On a Kilburn or Harlesden terrace within the Article 4 area, matching brick, mortar and window detail to the existing elevation is a specified requirement rather than a preference, and matched materials are consistently the item that surprises people on the final account.
Typical extension costs in Brent (build only)
On top of the build cost, you will need architectural drawings. These fees are 30% below typical London architect rates.
What moves the price of a Brent extension?
Brent's extension costs split along the same line as everything else here. Kilburn and Harlesden are dense Victorian terrace with no side access, so groundworks are slower and more expensive. Wembley's interwar semis have side passages. Over both sits an Article 4 Direction, 22 conservation areas, and a council that issued 399 enforcement notices in three years (MHCLG planning statistics, retrieved 1 September 2026) - unauthorised work is found in this borough.
Conservation areas
Brent has 22 designated conservation areas, including Queen's Park, Mapesbury, Kensal Green, Harlesden, Sudbury Court. If your property is in a conservation area, Permitted Development rights are restricted, meaning you may need a full planning application (£548 council fee). Conservation area applications also tend to require higher-quality materials and more sympathetic design, which can increase build costs by 10-20%.
Article 4 Directions
Brent has Article 4 Directions in place. Article 4 for HMO conversions in specific streets around Wembley and Harlesden. Where Article 4 applies, works that would normally be Permitted Development require a full planning application. This adds £548 to the council fee and typically 2-3 months to the project timeline, which can affect overall costs if you are renting alternative accommodation during the build.
Property type
The housing stock in Brent is predominantly edwardian villas in queen's park and mapesbury; victorian terraces in kilburn and harlesden; 1930s semi-detached in wembley; post-war tower blocks in church end. Victorian and Edwardian terraces typically suit side-return and rear extensions, while 1930s semi-detached properties are well suited to two-storey rear extensions. Detached houses offer the most flexibility but often have larger footprints, meaning higher absolute costs even if the per-sqm rate is similar.
Access and logistics
On a Kilburn or Harlesden terrace, spoil from the foundations leaves through the front door and every bag of cement comes in the same way. That is a labour cost, and it is the reason two identical extensions can differ substantially between one Brent postcode and another. A Wembley semi with a side gate avoids it. Establish which you have before comparing builder quotes.
Our drawing fees for Brent extensions
At Architectural Drawings London. No hourly billing, no surprises. Our fees cover everything needed for a valid planning submission to Brent Council and for building regulations approval.
Drawing fees for extensions in Brent
Every package includes a measured survey of your existing property, existing floor plans and elevations, proposed floor plans and elevations, a site plan, and a design and access statement where required. Our MCIAT chartered architectural technologists handle the full process from survey to submission, and we liaise with Brent Council on your behalf.
We cover all Brent postcodes: NW2, NW6, NW9, NW10, HA0, HA9.
Planning or permitted development in Brent?
Many house extensions in Brent can be built under Permitted Development (PD) rights without needing a planning application. Under PD, single-storey rear extensions can extend up to 6 metres from the original rear wall for terraced and semi-detached houses, or 8 metres for detached houses (under the Prior Approval process). However, Brent has Article 4 Directions that may remove some PD rights. Article 4 for HMO conversions in specific streets around Wembley and Harlesden.
Within Brent's 22 conservation areas, which one restriction matters depends on the half of the borough. On the Wembley semis it is the side extension. On the Kilburn and Harlesden terraces there is no side to build on, so the binding rule is the one on cladding and render, over stock whose designation rests on consistent brick. An Article 4 Direction removes more on top.
Two-storey extensions need full permission. In Brent the answer depends heavily on which part of the borough you are in: a first-floor addition in Wembley sits among stock that is already being substantially altered, while in Queen's Park and Mapesbury the Article 4 Direction and the conservation appraisal govern the elevation in detail. The two are not comparable proposals.
Brent issued 1,367 certificates of lawful development in three years (MHCLG planning statistics, retrieved 1 September 2026). In a borough with an Article 4 Direction covering part of it and an active enforcement team, that document does more work than in most of London: it is the answer when someone asks, years later, under what authority the extension was built. We prepare the drawings for it as part of the same package.
Frequently asked questions
How much does a house extension cost in Brent?
Build costs for a house extension in Brent typically range from £2,500 to £3,800 per square metre, as Brent is an inner London borough. A typical single-storey rear extension of 15-20 sqm would cost between £37,500 and £76,000 for the build alone. On top of build costs.
Can I extend under Permitted Development in Brent?
Inside Brent's 22 conservation areas the restriction that bites hardest is the one on materials. The Edwardian streets of Queen's Park and Mapesbury derive their designation from consistent brick, render and joinery, so a rear addition in anything that does not match will be resisted even where its size is unobjectionable. The Article 4 Direction removes further rights on top of that, street by street.
How long does a house extension take in Brent?
A typical house extension project in Brent takes 5-8 months from initial instruction to completion. This breaks down as: 2-3 weeks for measured survey and drawing preparation, 8 weeks for planning determination by Brent Council (if required), 2-4 weeks for building regulations approval, and 8-16 weeks for construction depending on the size and complexity of the extension.
Do I need a Party Wall Agreement for an extension in Brent?
A mid-terrace house in Brent has two adjoining owners and needs a notice to each. Foundations within three metres of a neighbour's, and any cutting into the shared wall, both engage the Party Wall etc. Act 1996. Given the borough's 39 breach-of-condition notices over three years (MHCLG planning statistics, retrieved 1 September 2026), keeping the award on file alongside the permission is worth the small effort.
What experience do you have with extensions in Brent?
We prepare extension drawings for properties across all Brent postcodes (NW2, NW6, NW9, NW10, HA0, HA9). Our MCIAT chartered architectural technologists understand Brent Council's policies, design guides, and local precedents. We have a council-ready drawing review across all 33 London boroughs.
