TL;DR — Key Facts
- Build cost per sqm: £2,500 – £3,800 (inner London borough)
- Our drawing fees: Essentials from £1,225 · Complete from £1,750
- Council planning fee: £258 (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
Extension costs 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 actual cost of your extension will depend on the size, specification, and complexity of the project. A basic rear extension with standard finishes will sit at the lower end, while a high-specification kitchen extension with bi-fold doors, underfloor heating, and bespoke joinery will sit at the upper end or above.
Typical extension costs in Brent (build only)
On top of the build cost, you will need architectural drawings. Our Essentials package starts from £1,225 for extension drawings including existing and proposed plans, elevations, and a site plan. Our Complete package from £1,750 includes full planning and building regulations drawings. These fees are 30% below typical London architect rates.
What affects extension costs in Brent
Several local factors affect extension costs in Brent. Understanding these before you start will help you budget accurately and avoid surprises.
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 (£258 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 £258 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
Terraced properties in Brent often have limited rear access, which can increase build costs by £3,000-8,000 due to the need to transport materials through the house. Properties with side access or rear lane access avoid this premium. Parking restrictions and CPZ zones in Brent can also add skip permit and parking suspension costs of £200-500.
Our drawing fees for Brent extensions
At Architectural Drawings London, we offer fixed-fee packages for house extension drawings. 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 vs 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.
Properties in Brent's 22 conservation areas have more restricted PD rights. In conservation areas, you cannot build side extensions under PD, rear extensions are more limited, and cladding changes require planning permission.
Two-storey extensions almost always require full planning permission. Brent Council generally expects two-storey extensions to be subordinate to the original dwelling, set in from the side boundary, and designed to avoid unacceptable loss of light or privacy to neighbouring properties.
We recommend obtaining a Lawful Development Certificate (£129) even for PD projects. This provides legal proof that your extension is lawful and is valuable when selling the property. We prepare the LDC drawings and application on your behalf.
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, you need architectural drawings (from £1,225 with us) and a council planning fee of £258 if planning permission is required.
Can I extend under Permitted Development in Brent?
Many single-storey rear extensions in Brent qualify as Permitted Development, allowing you to build without planning permission. You can extend up to 6 metres from the rear wall for terraced and semi-detached houses, or up to 8 metres for detached houses under Prior Approval. However, properties in Brent's 22 conservation areas have more restricted PD rights, and Article 4 Directions may further limit PD in some areas. We recommend applying for a Lawful Development Certificate (£129) to confirm PD eligibility.
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?
If your extension in Brent involves building on or near a shared boundary wall, excavating within 3 metres of a neighbour's foundation, or excavating within 6 metres to a depth below their foundation, you will need a Party Wall Agreement under the Party Wall etc. Act 1996. This is common for side-return extensions on terraced properties in Brent. A Party Wall surveyor typically costs £700-1,500 per neighbour. We can recommend Party Wall surveyors who work in Brent.
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 98% first-time approval rate across all 33 London boroughs. Our fixed fees start from £1,225 for extensions, which is 30% below typical London architect rates.