House extension drawings in Westminster

Houses, flats and mews: who can build what

Because so few Westminster households live in a house, many Westminster owners have a flat or maisonette rather than a house. Permitted development for extensions applies to houses, not flats, so a flat owner needs planning permission for anything that changes the outside of the building, and usually the freeholder's consent as well.

Gardens are scarce too. Domestic gardens made up just 7.9 per cent of the borough's land in the national Generalised Land Use Database, so extensions here tend to be small, tightly fitted additions where every metre has to be justified.

We draw each of these as a measured, single-model set, so the existing building, the neighbours' windows and the proposal sit on one datum. In dense streets, that accuracy lets the light and outlook tests be shown on the drawings rather than argued.

Permitted development, prior approval or a planning application

Where the house is outside a conservation area and has no Article 4 restriction, the national rule lets a single-storey rear extension go 3 m (attached) / 4 m (detached) beyond the original rear wall, single storey, at no more than 4 m high. A Lawful Development Certificate in Westminster puts that conclusion on paper for a buyer's solicitor.

A larger rear extension can go through prior approval at 6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSI. The council then has 42 days to respond before work may begin. That route is closed on conservation land, so in practice many Westminster extensions are householder applications.

A householder application costs £548 in council fees, paid to the council. Our planning drawings in Westminster are the set that application needs.

How Westminster decides householder applications

In its latest published year Westminster decided 366 householder applications and granted 82 per cent of them. 79 per cent were decided within eight weeks or an agreed extension.

Those figures cover every kind of householder work, from windows to extensions, so they describe the council, not your house. We use them to set a realistic timetable, and we do not use them to predict a decision.

What the extension drawings include and cost

A Westminster set shows the existing and proposed floor plans, elevations and sections, plus the location and block plans. Extension drawings start at £695 with VAT included, and the price is fixed before you commit. Drawings are normally ready about a week after the survey.

A second chartered technologist checks every sheet before it is submitted, and if the council asks for changes we redraw at no charge until approval. If the project touches a shared wall, the Party Wall Act applies: Adjacent excavation notice at least 1 month before work: within 3 m and deeper than the neighbour's foundations, or within 6 m and cutting a 45° line from their foundations.

The design also has to satisfy the energy rules in Approved Document L: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Householder applications are exempt from biodiversity net gain, and a residential extension can claim exemption from the community infrastructure levy before work starts.

Related drawings and neighbouring boroughs

Looking at one particular shape? See rear extension drawings in Westminster or double-storey extension drawings in Westminster. Adding a room in the roof instead? Try loft conversion drawings in Westminster. For the borough overall, start at architectural drawings in Westminster.

Across the boundary the guidance changes. Compare house extension drawings in Kensington and Chelsea or in Camden, or read the overview of house extension drawings across London.