Feasibility studies for London houses: what can you build, and how?
Before you pay for a full set of drawings, it is worth knowing whether the idea works. A feasibility study takes your address and your wish list, checks the constraints, tests the options against the rules and tells you which route costs least in time and money. We do it for a fixed £495.
Fixed fee from £495 · all prices
Prefer to talk it through?
The question most people ask first
Most owners start with 'can I do this?', and the honest answer depends on four things that are not visible from the street: what rights the house still has, what designations cover it, what the neighbours have already built and what the council's own policies say about your sort of project. A feasibility study answers all four before you have spent anything on detailed drawings.
It is also the least expensive place to change your mind. If a hip-to-gable loft turns out to be removed from permitted development by the area you live in, or the extension you imagined is longer than the rules allow, you learn it for a fraction of the cost of a full drawing set.
Feasibility Studies
from £495
Every price is the full fixed fee you pay. No VAT is charged. Council application fees are paid to the council separately.
What you get
- A check of the address: conservation area, Article 4, listing, flood zone and trees
- The planning route for each idea: permitted development, prior approval or planning permission
- Two or three options sketched at outline scale on the existing footprint
- The size limits that apply to each, set out against your plot
- Likely council fees, timescales and any levy exposure
- A written summary with our recommendation and the risks, in plain English
- What is the site?
Constraints and rights on the address, from designations to the history of earlier applications.
- What are the rules?
Which permitted development limits and local policies apply to your type of house.
- What fits?
Outline options on the plan, measured against those limits.
- Which route?
No application, prior approval, a certificate or full planning, with the time and fee for each.
- What next?
A recommendation, and the full drawing service to follow if you want to go ahead.
Permitted development has hard numbers
For an extension, the numbers are in Part 1, Class A of the General Permitted Development Order. A single-storey rear extension may not extend beyond the rear wall of the original house by more than 4 metres on a detached house, or 3 metres on any other, and may not exceed 4 metres in height. The enlarged part cannot be within 2 metres of the boundary if its eaves would exceed 3 metres.
A larger single-storey extension of up to 6 metres, or 8 metres on a detached house, goes through the prior approval process, and does not apply on article 2(3) land, which includes conservation areas. We lay these limits over your plan so you can see where each idea lands, with depth measured from the original house, not from a later extension.
Planning guidance says a council may charge for it, but the charge must not exceed the cost of providing the service.
What the study checks about the address
We search the council's constraint maps and register for the things that remove or restrict rights: a conservation area, an Article 4 direction, a listing on the house or beside it, a tree protection order, a flood zone, a protected view or a planning condition on an earlier permission that took permitted development away. Each can turn a no-application project into an application, and each changes the fee and the timetable.
We also read the planning history of the street. Applications approved or refused on neighbouring houses are strong evidence of how the officer reads the policy in practice, and a refusal two doors down for the same idea is something you want to know about before you spend money.
Time, fees and the levy
Each route has a different clock. A planning application for development that is not major has a statutory decision period of 8 weeks from receipt. The householder fee from 1 April 2026 is £548. Prior approval and certificate routes have their own fees and periods, and we put them side by side for your project.
The Community Infrastructure Levy can catch larger schemes. Government guidance says the levy may be payable where the new build floor area is 100 square metres or more, in areas where the council charges it, although extensions and annexes can attract reliefs and exemptions. We say where your scheme sits against that line, so there are no surprises.
Should you talk to the council first?
Many councils offer paid pre-application advice. Planning guidance says a council may charge for it, but the charge must not exceed the cost of providing the service. It can make sense for a contested project, such as a mansard on a terrace with an intact roofline. For a straightforward rear extension, the written advice often adds little to what a study already tells you.
The study says whether we think pre-application advice is worth it for your project, and what question to put to the council if it is. If it is not, we say so, and you save the fee.
What it costs, and what happens next
The fixed fee is £495, the total you pay, with no VAT charged. It is a written study, not a set of drawings for submission, and it does not guarantee that the council will approve anything. What it gives you is a clear idea of what is allowed, what is likely and what is risky.
If you go ahead, the next step is the matching drawing service, and the survey and outline work in the study carries forward. Start with the form at the top of this page: your address, your idea and your budget in a few lines.
Sources
Every figure on this page, where it comes from and a link to the original.
| Figure | Source | Link |
|---|---|---|
| 3 metres | GPDO 2015 Sch 2 Pt 1 Class A.1(f)(i): a single-storey enlargement may not extend beyond the rear wall of the original dwellinghouse by more than (source wording: "3 metres in the case of any other dwellinghouse") | www.legislation.gov.uk |
| 4 metres | GPDO 2015 Sch 2 Pt 1 Class A.1(f): (source wording: "4 metres in the case of a detached dwellinghouse"; and "exceed 4 metres in height") | www.legislation.gov.uk |
| 2 metres | GPDO 2015 Sch 2 Pt 1 Class A.1(i): not permitted where the enlarged part (source wording: "would be within 2 metres of the boundary of the curtilage of the dwellinghouse, and the height of the eaves of the enlarged part would exceed 3 metres") | www.legislation.gov.uk |
| 6 metres | GPDO 2015 Sch 2 Pt 1 Class A.1(g): for a dwellinghouse not on article 2(3) land nor on a site of special scientific interest (source wording: "8 metres in the case of a detached dwellinghouse, or 6 metres in the case of any other dwellinghouse") | www.legislation.gov.uk |
| article 2(3) land | GPDO 2015 Sch 2 Pt 1 Class A.1(g): the larger single-storey depths apply only to a dwellinghouse (source wording: "not on article 2(3) land") | www.legislation.gov.uk |
| 8 weeks | Town and Country Planning (Development Management Procedure) (England) Order 2015 art 34(2)(b): application for development which is not major development (source wording: "8 weeks beginning with the day immediately following that on which the application is received") | www.legislation.gov.uk |
| £548 | Statutory fee from 1 April 2026: householder planning application, Sch 1 Pt 2 category 6(1) | assets.publishing.service.gov.uk |
| 100 square metres | Planning Practice Guidance, Community Infrastructure Levy, para 003: (source wording: "the gross internal area of new build is 100 square metres or more") | www.gov.uk |
| must not exceed the cost of providing the service | Planning Practice Guidance, Before submitting an application, para 003: (source wording: "Where charges are made they must not exceed the cost of providing the service") | www.gov.uk |