Westminster, London
L-shaped dormer drawings in Westminster
L-shaped dormer drawings in Westminster begin with the council's own roof guidance, the Roofs: a guide to alterations and extensions on domestic buildings SPG. The borough is heavily protected: 56 conservation areas and 4,015 listed entries mean the L-shape is nearly always a planning application, and we price it as a fixed quote after a free constraints check.
Fixed quote after a free constraints check
- MCIAT chartered
- £2m PI insured
- LABC Partnered
- Fixed fees, VAT included
Request a fixed quote
How we work on l-shaped dormer drawings
Nine steps from first call to approval.
Enquiry and constraints check
We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.
Measured survey
We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.
Design options
We model the house in Revit and show you options in 3D and plan, with the planning strategy and the precedents in your street.
Design frozen
You choose an option in writing. Nothing changes after this without your say.
Independent check
A second chartered technologist checks every sheet against the council's validation checklist and the policy. A senior review signs it off before anything is submitted.
Submission
We prepare the forms, certificates, fee and documents and submit through the Planning Portal.
Officer liaison
We answer the planning officer and make any amendments within five working days, at no charge until approval.
Building regulations
Technical drawings are coordinated with the structural engineer's calculations, the drainage and the planning conditions.
Approval and hand-over
Building control approval, then a next-steps pack covering the commencement notice, party wall timing and CIL.
Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.
Request a fixed quote
What Westminster's roof guidance asks of a dormer
Westminster publishes the Roofs: a guide to alterations and extensions on domestic buildings SPG, and for the backs of streets and courtyards it adds the Mews: a guide to alterations SPG. Between them they decide how much new roof an officer will accept on a terraced house or a mews building, and they treat the original roofline as something to protect.
The city plan behind them is the City Plan 2019-2040 (2026), adopted in 2,026, so the policy wording is recent. We read the guidance against your own building: where the outrigger sits, how visible the roof is from neighbouring windows, and whether neighbours have already altered theirs.
That reading becomes the design brief. A full L may be reasonable at the back of a stuccoed terrace and unthinkable on a listed one, so we say which situation you are in before drawing.
Local figures for Westminster
| Measure | Value | Period | Source |
|---|---|---|---|
| Conservation areas | 56 named conservation areas published by the council | — | planning.data.gov.uk |
| Article 4 directions | 10 Article 4 directions published by the council | — | planning.data.gov.uk |
| Listed building entries | 4,015 list entries (Historic England, within the LPA boundary) | — | planning.data.gov.uk |
| Households living in a house | 10.2 % of households living in a house or bungalow (detached, semi-detached or terraced) | Census 2021 | nomisweb.co.uk |
| Average price, terraced | 1,616,250 GBP | 2026-07 | publicdata.landregistry.gov.uk |
| Householder decisions | 366 decisions | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| Householder applications granted | 82 % | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| Householder applications decided in time | 79 % decided within 8 weeks or an agreed extended period | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| GPDO 2015 Sch 2 Pt 1 Class B, para B.1(d) | 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume | — | legislation.gov.uk |
| Class B, para B.1(f) | Class B roof enlargements are not permitted development on article 2(3) land | — | legislation.gov.uk |
A blank value means the figure has not been published, not that there are none. Check your own address with the council.
Householder applications by street in Westminster
| Street | Applications | Approved |
|---|---|---|
| Randolph Avenue | 16 | 79% |
| Ashworth Road | 13 | 85% |
| Clifton Hill | 11 | 70% |
| Ponsonby Place | 10 | 100% |
| Lancaster Mews | 9 | 38% |
| Westbourne Park Road | 9 | 88% |
| Carlton Hill | 8 | 86% |
| Kilburn Lane | 8 | 86% |
| Sutherland Place | 8 | 63% |
| Wilton Row | 8 | 100% |
| Caroline Close | 7 | 33% |
| Chester Row | 7 | 100% |
| Greenberry Street | 7 | 57% |
| Hereford Road | 7 | 60% |
| Hyde Park Gardens Mews | 7 | 75% |
Loft enlargement in section: the permitted development limits
A dormer on the rear slope, with the limits that decide whether it needs planning permission.
- A · Extra roof volume allowed
- 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume
- B · Set-back from the eaves
- Original eaves maintained; enlargement set at least 0.2 m from the eaves measured up the roof slope, so far as practicable (not required for hip-to-gable or roofs joining a rear/side extension)
- C · Height limit
- No part higher than the highest part of the existing roof
Designations that stack up on one address
Many Westminster houses sit under more than one control. The council publishes 10 Article 4 directions, Historic England lists 4,015 entries (including 205 at Grade I and 373 at Grade II*), and the borough contains 1 World Heritage Site.
A dormer inside a conservation area is a planning matter by national rule: Class B roof enlargements are not permitted development on article 2(3) land. A listed house needs consent on top. We pull the entry, the area appraisal and any direction first, so the application names every designation that applies.
Few houses, high stakes
Only 10.2 per cent of households here live in a house, so a roof extension is a significant private investment. A terraced home averages 1,616,250 pounds, against 876,788 pounds across every property type.
That value justifies drawings built to survive close scrutiny. We survey the roof structure and the outrigger together, since an L-shaped dormer joins them and the junction detail is where most of the cost lies.
How Westminster decides householder applications
In the latest year the council decided 366 householder applications, granted 82 per cent and decided 79 per cent in time. Those are borough-wide figures for every kind of home project.
Nothing here predicts your outcome, and we never promise one. It does suggest that a first-submission set answering the guidance point by point is worth the extra drawing time.
National rules we apply to the L
Where the new roof meets a rear extension roof, the rule says: Eaves-retention and 0.2 m set-back do not apply where the enlargement joins the original roof to the roof of a rear or side extension. Volume is limited to 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume, with this height limit: No part higher than the highest part of the existing roof.
Stairs must achieve headroom as follows: Loft conversions where 2.0 m cannot be achieved: 1.9 m at the centre of the stair, 1.8 m at the side (half width). Party structures need notice: Party structure notice at least 2 months before work. Our wider L-shaped dormer drawings guide covers these for every borough.
Mews roofs and townhouse roofs behave differently
A mews house has a shallow roof, a narrow plot and neighbours a few metres away, so privacy and daylight dominate the officer's reading. A stucco townhouse has a tall rear elevation and a butterfly or pitched roof behind a parapet, so visibility from the street is the issue. The same L-shape is judged on different grounds in each.
For a townhouse we study the parapet line, the closet wing and any lightwell, and show how the dormer sits behind them. For a mews we draw sightlines from the windows opposite and test how much sky the neighbours keep. Both studies go onto the sheets, so the officer finds the answer on the page.
Costs the council adds on top of drawing fees
A Westminster scheme that creates new floorspace can attract the borough's community infrastructure levy, charged at different rates across Prime, Core and Fringe zones. An L-shaped dormer that adds a lot of habitable area is worth checking against it before you commit.
We flag the levy form at the start and tell you whether your proposal is likely to trigger it, so the figure does not arrive after the decision.
What you get and where to look next
Expect existing and proposed plans, a roof plan, the junction sections and elevations, with a second MCIAT chartered technologist checking every sheet. We redraw at no charge until approval if the council asks for changes.
If the full L is too much, dormer loft conversion drawings in Westminster may fit. See architectural drawings in Westminster for the borough overview, or L-shaped dormer drawings in City of London next door.
What you receive
Related pages
Other services in Westminster
Questions
Which Westminster guidance covers dormers?
The council's Roofs: a guide to alterations and extensions on domestic buildings SPG and, for mews, the Mews: a guide to alterations SPG.
Do I need planning permission for an L-shaped dormer in Westminster?
Almost always. With 56 conservation areas, the national rule applies: Class B roof enlargements are not permitted development on article 2(3) land.
How many householder applications does Westminster grant?
It granted 82 per cent of 366 householder decisions in the latest year.
Is a listed house different?
Yes. It needs listed building consent as well, and the borough has 4,015 listed entries.
Sources and dates
- planning.data.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- nomisweb.co.uk, retrieved
- publicdata.landregistry.gov.uk, retrieved
- assets.publishing.service.gov.uk, retrieved
- legislation.gov.uk, retrieved
- westminster.gov.uk, retrieved
- westminster.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- gov.uk, retrieved
- legislation.gov.uk, retrieved
- Contains public sector information licensed under the Open Government Licence v3.0.
- Contains OS data © Crown copyright and database right 2026.
- Contains HM Land Registry data © Crown copyright and database right 2026. This data is licensed under the Open Government Licence v3.0.
- Contains Historic England data © Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026.
Tell us about your property.
We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.