Cornwall Terrace beside Regent's Park: a long cream stucco Regency terrace with a colonnade of columns and a row of tall sash windows — Photograph: ell brown (CC BY 2.0)

01Advice before you buy or design

A feasibility study for your London house

Before the full drawings, the question is simpler: what can this house take, and what will it cost to find out? We survey the constraints, test your ideas against the rules, and show two or three options in plan and 3D, with the route and the fees. From £545, fixed before we start.

From £545

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02The fee

One fixed fee, published

Feasibility and options study

from £545

The total you pay. No VAT to add.

Ask for your fixed fee

What you get

A written check of the address: listing, conservation area, rights removed, trees, flood
Two or three options sketched in plan and 3D, with the floor area each gives you
The planning route for each: permitted development, prior approval or an application
Council fees and likely timescales for each route, with the risks stated plainly
A recommendation, and the fee for taking the chosen option to full drawings

The study is credited against our drawings if you go ahead, and our fee carries no VAT to add. Council fees are paid to the council.

03How it runs

From a wish list to a chosen option

We draw for the council only after you pick an option, in writing.

Rows of brick terraced houses and gardens on a residential street — Photograph: Altaf Shah

04Advice before you buy or design

Cheaper to change a sketch than a building

A feasibility study is the least expensive moment to be wrong. A rear extension that reaches 3 m is a different route from one that reaches 6 m, and a loft with a rear dormer is a different route from one with a front roof window. Seeing both on paper, with their fees and risks, lets you choose before anything is submitted.

We model the house in 3D so you can walk round each option. A kitchen that gains a metre looks very different when the neighbour's window is in the picture, and our drawings show it.

A row of colour-washed Victorian terrace houses on Falkland Road in Kentish Town under a blue sky — A Kentish Town terrace: the neighbours' windows to either side decide the depth of any rear option.Photograph: Images George Rex, CC BY-SA 2.0

05Advice before you buy or design

The tests every option has to pass

Each option is run through the same checks. Is the house a single dwelling, or a flat, which has no householder permitted development? Is it in a conservation area, where side extensions and cladding rights are removed? Do the buildings you would add cover less than half the garden?

Then comes the neighbour test. Councils often use a 45-degree line from the centre of the nearest ground-floor window, as Merton's design guidance does, and we draw that line on the plan. The study ends with a clear answer to which options are low-risk and which depend on an officer's judgment.

Sheets are written so two options can be laid side by side and compared.

06Advice before you buy or design

What happens after you choose

The study fee is credited against our drawings, so the work you paid for is not paid twice. If you choose to proceed, the sketches become the first design stage and the full survey follows; if not, you keep a dated report you can show a lender, a partner or another designer.

From there the route is usually planning drawings or a Lawful Development Certificate, and for a larger house the study often leads to a loft conversion or a rear extension set.

Red-brick Queen Anne style houses on Marlborough Crescent in Bedford Park with white sash windows and tall chimneys — Bedford Park: deep gardens give the options room, but the street's red-brick character sets the limits.Photograph: stevecadman, CC BY-SA 2.0

07The record

Figures that shape the job

Half
The most of the garden that buildings other than the original house may cover under permitted development.
Source: General Permitted Development Order 2015, Schedule 2, Part 1, Class A, checked 15 Oct 2026
3 m / 4 m
How far a single-storey rear extension may project from an attached and a detached house without an application.
Source: General Permitted Development Order 2015, Schedule 2, Part 1, Class A, checked 15 Oct 2026
40 m³
Roof volume a terraced house can add under the loft rules; 50 cubic metres for other houses.
Source: General Permitted Development Order 2015, Schedule 2, Part 1, Class B, checked 15 Oct 2026
45°
The angle some councils apply from the neighbour's nearest ground-floor habitable room to limit a rear projection.
Source: Merton Council, Small Sites Toolkit 01 Design Guidance, paragraph 6.1.11, checked 17 Oct 2026
£548
What the council charges to decide a householder planning application, from 1 April 2026.
Source: Ribble Valley Borough Council, national fee table from 1 April 2026, checked 17 Oct 2026
8 weeks
How long a council has to decide a non-major planning application once it is valid.
Source: Development Management Procedure Order 2015, article 34, checked 15 Oct 2026
No flats
A flat, or a building that contains flats, has no householder permitted development rights to test.
Source: General Permitted Development Order 2015, article 2, checked 15 Oct 2026

08Questions

What clients ask before they instruct us

Is a feasibility study worth it for a small extension?

Often yes, when more than one option is on the table or the address is constrained. For a plain 3 m rear extension on an unconstrained house, we may go straight to drawings and say so.

How is the fee credited?

The £545 study fee is taken off our drawings fee if you instruct us. We show the credit on the quote.

Will the study tell me what the building work costs?

It gives council fees and our fees, not builders' prices. Build cost depends on the specification and the market, and we do not guess it.

Do you survey the house for a study?

We work from the constraints and your measurements at this stage. A full measured survey follows when you choose an option and move to drawings.

Can I use the study with another designer?

Yes, it is yours. Most clients move to full drawings with us, and if the house is listed we can add a heritage statement.

09Related

Kensington street lined with brick townhouses and lit streetlamps beneath an orange dusk sky

Send us the address of your house.

We look up the conservation area, listing and Article 4 position, then reply with a fixed fee. A message before 3pm is answered the same working day.

Ask for a fixed fee Call 020 7131 9703 WhatsApp