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GPDO 2015 England Permitted Development rules · statutory fees effective 1 April 2026

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Extensions & Lofts Schedule 2, Part 1 · Class B · 40/50m³

Loft Conversion & Dormer Planning Rules (Class B Volume Checker)

Most rear dormer and hip-to-gable loft conversions are Permitted Development under GPDO Part 1 Class B, provided the extra roof space stays within 40m³ for terraced houses or 50m³ for semi-detached and detached houses. Dormers must not face the road, rise above the ridge, or sit tight to the eaves. Test your loft design below.

If PD
£0
Application
£548
Decision
8 wks

Step 1 · Your project

Loft Conversions checker

House type
42m³

Include the dormer, any hip-to-gable infill and previous roof extensions. Your designer can calculate this from the drawings.

Is there a dormer on the front roof slope facing the road?
20cm

Measured along the roof plane. 20cm is the standard; less is only acceptable where it genuinely isn’t practicable.

Will any part be higher than the existing ridge?
Side-facing windows in the new roof space
Balcony, roof terrace or raised platform?
Is the house on Article 2(3) land (e.g. a conservation area)?

Rules reflect the GPDO 2015 (England) for houses. Flats, maisonettes, listed buildings and Article 4 areas have restricted rights. Disclaimer.

Step 2 · Live statutory assessment

Permitted Development – Class B

Class B · 40/50m³

Your 42m³ loft conversion is within the Class B limits for a Semi-detached / detached house. Building Regulations approval is still required.

  • Additional volume 42m³ is within the 50m³ allowance.
  • No enlargement on the front roof slope.
  • Nothing rises above the existing ridge.
  • Eaves setback of 20cm meets the 20cm standard.
ROOF SECTION – DORMER POSITION & VOLUME
EXISTING RIDGE 20cm SETBACK FRONTREAR ADDED VOLUME 42m³ALLOWANCE 50m³

England fees & timings (from 1 April 2026)

Council application fee

£0

Class B Permitted Development

Lawful Development Certificate

£274

Strongly advised – lenders ask for it

Decision time

0 weeks

LDC takes ~8 weeks if chosen

Applying online via the Planning Portal adds a £91 service charge (inc. VAT).

Builder & neighbour spec sheet

Export these exact limits and your answers to share with your contractor.

At a glance

Loft Conversions: the statutory limits in England

  • Additional roof volume max 40m³ (terraced) or 50m³ (semi-detached and detached), including any previous roof enlargements.
  • No enlargement may extend beyond the plane of the roof slope that forms the principal elevation and fronts a highway.
  • No part may be higher than the highest part of the existing roof.
  • So far as practicable, dormers must be set back at least 20cm from the original eaves, measured along the roof slope.
  • Side-facing windows must be obscure-glazed and non-opening unless the opening part is more than 1.7m above the floor.
  • No verandas, balconies or raised platforms; materials must be of similar appearance to the existing house.

Statutory reference

Legislation summary & 2026 fee table

England statutory planning fees effective 1 April 2026. Wales, Scotland and Northern Ireland operate different regimes.

GPDO legislation and fee summary for Loft Conversions & Dormers
Primary legislation Town and Country Planning (General Permitted Development) (England) Order 2015 (SI 2015/596), as amended
GPDO Schedule / Part Schedule 2, Part 1
Class Class B – additions or alterations to the roof
Exact reference GPDO 2015 Sch.2 Pt.1 Class B, B.1(a)–(g), B.2(a)–(c); Class C (rooflights)
Standard application fee £548 – Householder planning application
Lawful Development Certificate (proposed) £274 – optional proof the works are lawful
Planning Portal service charge £91 (inc. VAT) if submitted online
Council determination period 8 weeks
Key exclusions Class B does not apply on Article 2(3) land (conservation areas, National Parks, National Landscapes, Broads, WHS) or to flats.

Avoid enforcement

The 3 most common homeowner traps

Trap #1

Miscalculating the volume

Volume is measured externally and includes hip-to-gable infill as well as the dormer box. A typical full-width rear dormer on a semi is 35–45m³; add a hip-to-gable and you can pass 50m³ quickly. Any roof extension added by a previous owner also counts against the allowance.

Trap #2

Misreading ‘principal elevation’

The front-dormer ban applies to the roof slope forming the principal elevation and fronting a highway. On corner plots the side slope may also front a highway, and the principal elevation is not always the side with the front door. If unsure, get an LDC.

Trap #3

Ignoring the party wall

Hip-to-gable conversions on semis usually build up the party wall and insert steels into it. That is notifiable work needing two months’ Section 2 notice – a common cause of delayed start dates.

Separate legal regimes

Building Regulations vs planning permission

Converting a loft into a habitable room always needs Building Regulations approval, even when Class B covers the planning side:

Fire escape (Part B)
A new storey over 4.5m above ground usually requires a protected stairway to a final exit, fire doors to habitable rooms and mains-wired interlinked smoke alarms.
Stairs and headroom (Part K)
Loft stairs need 2.0m headroom (reducible to 1.9m at the centre and 1.8m at the side under a sloping ceiling) – often the deciding design constraint.
Structure (Part A)
New floor joists, steel beams and padstones need structural calculations; existing ceiling joists are rarely adequate as a floor.
Insulation and ventilation (Parts L and F)
Roof and dormer cheeks must meet current U-values, with condensation control and purge ventilation for the new room.

Under the Party Wall etc. Act 1996, cutting into a party wall for beams, raising it for a hip-to-gable or removing chimney breasts on it requires a Section 2 notice at least two months before work. If the neighbour does not consent within 14 days, a dispute is deemed and surveyors must agree a party wall award.

FAQs

Loft Conversions: frequently asked questions

How much volume can I add with a loft conversion without planning permission?

40m³ for terraced houses and 50m³ for semi-detached and detached houses, measured as the additional volume of the roof space and including previous roof extensions. Above that, you need a householder application (£548 in England from April 2026).

Do I need planning permission for a Velux (rooflight) loft conversion?

Usually not. Rooflights fall under Class C: they must not project more than 150mm from the roof slope, not rise above the highest part of the roof, and side-facing ones must be obscure-glazed and non-opening below 1.7m. Building Regulations still apply to the conversion.

Do I need a party wall agreement for a loft conversion?

In most terraced and semi-detached houses, yes. Inserting steels into or raising the party wall is Section 2 work requiring two months’ notice. Your neighbour can consent in writing; otherwise a party wall surveyor prepares an award.

Can I build a dormer in a conservation area?

Not under Permitted Development – Class B does not apply on Article 2(3) land. You need a householder planning application, and councils generally expect dormers there to be modest, set well within the roof and finished in traditional materials.

Sources: The Town and Country Planning (General Permitted Development) (England) Order 2015 and amendments (legislation.gov.uk); MHCLG ‘Permitted development rights for householders: technical guidance’; the Town and Country Planning (Fees for Applications…) (England) Regulations 2012 as amended; Building Regulations 2010 Approved Documents; Party Wall etc. Act 1996. Last reviewed 15 October 2026. See our editorial standards and disclaimer.

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