Side extension in Brent: Planning Permission Guide
A complete guide to building a side extension in Brent, covering permitted development rules, costs, and professional requirements.
Based on 40 decided applications in Brent over 12 months (34 granted, 6 refused).
Brent has conservation areas around Wembley Park, Sudbury Court, Kensal Green, and Queen's Park. Article 4 Directions restrict specific rights in some conservation areas. Listed buildings cluster around Wembley and around historic Kensal Green Cemetery. The borough has a mix of Victorian terraces in the south and inter-war semis in the north. Kensal Green Cemetery and its surroundings have specific heritage considerations.
Personalised odds
5 nearest comparables & refusal reasons for your address.
Get my report — £9See a sample →Recent side extension decisions in Brent
The 5 most recent decided applications. Addresses redacted to postcode area.
Proposed single storey side infill to rear wrap around extension, rear double dormer roof extension, front and rear rooflights, changes t…
A proposed side extension to ground floor flat and erection of an outbuilding to contain a garden office and replacement of windows.
Conversion of single dwelling house into 2x self-contained flats with demolition of rear sheds and proposed single storey side infill ext…
Demolition of garage and proposed two-storey side extension, hip-to-gable roof extension, rear dormer extension with Juliet balcony and i…
Proposed single storey side to rear wraparound extension to the dwellinghouse.
These are borough-wide. See the 5 nearest to your address.
Get my report — £9Permitted Development Rules
Enlargement, improvement or other alteration of a dwellinghouse
GPDO 2015, Schedule 2, Part 1, Class A
Side extensions are also covered by Part 1, Class A of the GPDO. They must be single storey and cannot exceed half the width of the original house.
Key dimension limits
These are the maximum GPDO limits for a detached house with no constraints. Your actual limits depend on your property type, location, and any planning restrictions.
Enter your postcode to see the personalised limits for your side extension.
Check my limitsTypical Costs in London
Side extension costs in London depend on the width of your side return and the specification of the build.
Cost per m²
construction rate
Typical total
Based on 10–18 m²
Typically includes
Typically excludes
Costs vary depending on whether the side return is narrow or full-width.
Get a personalised cost estimate based on your actual side extension dimensions.
Get my estimateWhich Professionals Do You Need?
For a side extension, you'll typically need drawings for Building Regulations approval and may need a party wall surveyor if you share a boundary.
You'll need a party wall surveyor for this project.
A draughtsperson or architectural technician can prepare the plans needed for a single storey extension. A full architect may not be necessary.
Typical fee: £1,500–£3,500 (Plans + Building Regs)
Single storey extensions typically need structural calculations for any openings in existing walls and for foundations.
Typical fee: £500–£1,500
Your semi-detached house shares a boundary with neighbours. Extensions and loft work within 3 metres of a shared wall trigger the Party Wall Act.
Typical fee: £700–£1,500 (per neighbour)
This guidance is based on a typical semi-detached house with no special constraints. Listed buildings, conservation areas, and attached properties may require additional professional input.
Find out exactly which professionals you need for your side extension.
Get personalised guidanceConservation Areas & Listed Buildings
Side extensions are not permitted development in conservation areas or Areas of Outstanding Natural Beauty. You will need to apply for full planning permission.
Properties in conservation areas often have reduced permitted development rights. Some project types (like side extensions) lose PD rights entirely. An Article 4 Direction can remove additional PD rights.
Listed buildings (Grade I, II*, or II) have no permitted development rights at all. Any external alteration requires Listed Building Consent in addition to any planning permission. An architect experienced in heritage work is essential.
Check if your property is in a conservation area or has other planning constraints.
Check my propertyFrequently Asked Questions
Just want a quick yes/no for your side extension?
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