Loft conversion in Westminster: Planning Permission Guide
Everything you need to know about loft conversions in Westminster — permitted development rules, costs, and which professionals you'll need.
Check if your loft conversion qualifiesLoft conversions in Westminster at a glance
application fee
weeks typical
The City of Westminster has the densest concentration of conservation areas and listed buildings in the UK, covering almost the entire borough. Article 4 Directions layer on top of this in many areas, restricting virtually any external alteration. Listed building consent is required frequently in addition to planning permission. The council's design expectations are among the most stringent in the country — professional planning advice is essential.
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Approval probability, 5 nearest comparables, refusal reasons — for your specific address.
Recent loft conversion decisions in Westminster
The 5 most recent decided applications. Addresses redacted to postcode area.
Lower ground floor rear infill extension with terrace above, replacement of rear first floor conservatory, new roof level rear single dor…
Installation of photovoltaic panels at main mansard roof level and to rear first floor flat roof.
Erection of a dormer to the rear elevation.
Replacement of windows on the front facade, replacement of garage doors on the front elevation, reconstruction of the roof by extending t…
Erection of a mansard extension at fifth floor level.
These are borough-wide. See the 5 nearest to your address.
Get my report — £9Permitted Development Rules
Additions etc to the roof of a dwellinghouse
GPDO 2015, Schedule 2, Part 1, Class B
Loft conversions fall under Part 1, Class B of the GPDO. You can add volume to your roof space without planning permission, as long as you stay within the cubic metre limits for your property type.
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 loft conversion.
Check my limitsTypical Costs in London
Loft conversion costs vary significantly depending on the type — a simple Velux conversion is much cheaper than a dormer or mansard.
Cost per m²
construction rate
Typical total
Based on 15–25 m²
Typically includes
Typically excludes
Dormer loft conversions are at the higher end. Velux/rooflight conversions are cheaper. Mansard conversions can exceed these ranges.
Get a personalised cost estimate based on your actual loft conversion dimensions.
Get my estimateWhich Professionals Do You Need?
Loft conversions involve structural alterations to your roof and floor, so professional input is important for safety and Building Regulations compliance.
You'll need a structural engineer and a party wall surveyor for this project.
Loft conversions involve structural alterations and Building Regulations requirements that benefit from professional design.
Typical fee: £2,000–£5,000 (Plans + Building Regs)
Loft conversions require structural calculations for floor strengthening, roof alterations, and any steelwork.
Typical fee: £800–£2,500
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 loft conversion.
Get personalised guidanceConservation Areas & Listed Buildings
In conservation areas, dormers on any roof slope facing a highway are not permitted development. Velux or rooflight conversions may still be possible.
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 loft conversion?
Run our free 2-minute check to see whether your project likely qualifies as permitted development in Westminster. For personalised approval odds and nearby comparables, get the full report above.
Free 2-min check