Rear and side extensions
Single-storey rear, side return and wraparound extensions that open up the ground floor and bring in light. We design around how you cook, eat and live.
Get a quote for rear and side extensions
Planning drawings and architectural design in London
Extensions, loft conversions and new layouts, designed, drawn and submitted for planning on a fixed fee.
Fixed fees: flats from £1,950, houses from £2,700
What clients say
“Hassle free”
Chris Chelsea
“Delighted with the designs”
Mary Wandsworth
“Great service”
Nathan Clapham
Design your London home, in one place
From the first site visit to a submitted planning application, we manage the whole design and planning process for you. You get one studio, one fixed fee and one point of contact.
Know your fee upfront
Fixed-fee packages, priced in 60 seconds with our instant calculator. No hourly surprises.
Designed with planning in mind
Clear, refined designs with the plans, elevations and sections councils expect, backed by a working knowledge of London planning.
We handle the council
We submit your application and act as your agent until you have a decision.
Recent projects
A selection of homes we've designed across London, from side return extensions and loft conversions to reconfigured internal layouts for full-house refurbishments.
Side extension, Clapham
We reconfigured the existing layout to create an open-plan kitchen, dining and living space, a utility room and a WC.
View projectRear extension, Fulham
A rear extension with bifold doors, and a new kitchen with exposed brick under a full-width rooflight.
View projectLayout reconfiguration, Chelsea
An open-plan kitchen and living space, with a bespoke dark oak kitchen, period coving and a log burner.
View projectLayout reconfiguration, Chelsea
A new open-plan kitchen and living space and a reconfigured master bedroom.
View projectLoft conversion, Islington
A new living space and guest bathroom, with bifold doors opening onto a private roof terrace.
View project
How it works
Four stages from your first call to a planning decision. We manage the whole process for you, from the measured survey and design drawings to your planning decision notice.
1. Brief and survey
We start with your brief: how you live, what you need and your budget. Then we carry out a full measured survey and flag any site constraints before design begins.
2. Concept design
We develop initial layouts with zoning, configuration options and materials, so you understand how the space will work before we go into detail.
3. Developed design
We refine the design with you through to sign-off, then produce the full drawing set: plans, elevations, sections and supporting documents.
4. Planning application
We submit the application and act as your agent with the council. Validation takes around two weeks, and the decision usually follows within 8 to 12 weeks.
Extensions, loft conversions and layouts
We specialise in residential projects across London, from a side return in a Victorian terrace to a full rethink of a family home.
Loft conversions
Turn an unused loft into an extra bedroom, bathroom or workspace, whatever the shape of your roof. We make the most of every centimetre of headroom and get the stair right.
Get a quote for loft conversions
Layouts and interior design
Reconfigured layouts, internal walls moved and new rooms created. We plan the flow of the whole home, then bring in materials and finishes.
Get a quote for layouts and interior design
Fixed-fee packages
Pick the level of support you need. Prices depend on your property and project, so get an exact quote in 60 seconds.
Package 1
Drawings
Survey and full planning drawings
From £2,700
- Measured survey of your property
- Concept layouts and design options
- Full planning drawing set: plans, elevations, sections
Package 2
Planning
Everything in Drawings, submitted for you
From £3,050
- Everything in Drawings
- Planning application submitted for you
- We act as your agent and deal with the council
Package 3
Complete
Planning plus a photoreal visual
From £3,550
- Everything in Planning
- 1x photoreal 3D visual of your new space
- See finishes and light before you build
Council planning application fees are paid separately. Measured survey included in every package.
Get Instant QuoteInterior design and 3D visuals
See your new space before a single brick is laid.
We bring layouts to life with photoreal visuals, so you can test light, materials and finishes and make decisions with confidence. One visual comes with our Complete package, and more can be added to any project.
Add visuals to my quote
Planning drawings across London
We're based in Clapham and design homes across the capital. We know how London councils think about rear extensions, side returns, dormers and conservation areas, and we design to give your application the best chance first time.
- Wandsworth
- Lambeth
- Southwark
- Kensington and Chelsea
- Hammersmith and Fulham
- Merton
- Islington
- Camden
Ready to start your project?
Tell us about your project and we'll reply within one working day. We'll talk through your plans, flag planning constraints early and give you a realistic sense of scope and cost, with no obligation.
Prefer email? info@jcastudios.co.uk
Frequently asked questions
How much do planning drawings cost in London?
It depends on your property, the type of project and how much support you need. Every package is fixed-fee, so you know the full price before we start. Answer a few quick questions in our design cost calculator for an instant quote.
Get Instant QuoteWhat are the council fees for a planning application in London?
Planning application fees are set nationally, so they're the same at every London borough. From 1 April 2026:
| Planning application to extend or alter a house or flat | £548 |
|---|---|
| Lawful Development Certificate (permitted development) | £274 |
Fees usually rise each April. They're paid to the council when the application is submitted and aren't included in our packages.
Do I need planning permission for my extension or loft conversion?
Not always. Many single-storey rear extensions and loft conversions on houses can be built under permitted development, within size and design limits. Flats, conservation areas and listed buildings usually need full planning permission. We check which route applies at the start, and if your project falls under permitted development we can apply for a Lawful Development Certificate to confirm it.
How long does planning permission take?
Once submitted, an application usually takes around two weeks to be validated by the council. The decision then typically takes 8 to 12 weeks, after which you receive a formal Decision Notice. Getting drawings right first time is the best way to avoid delays.
What's included in a measured survey?
We visit your property and measure it accurately, noting anything that could affect the design, such as levels, structure and boundaries. This becomes the set of existing drawings that your new design is built on.
Do you submit the planning application for me?
Yes. With our Planning and Complete packages we prepare and submit the application, act as your agent and deal with the council until a decision is made. The council's own application fee is paid separately.
What happens if my planning application is refused?
We'll go through the planning officer's reasons with you and explain your options. Most often that means adjusting the design and resubmitting, though an appeal is sometimes the better route.
Do you design for flats as well as houses?
Yes. Our fees are split by property type, so flats are priced separately from houses. External changes to flats usually need full planning permission, and if you're a leaseholder you'll normally need your freeholder's consent too.
Which areas of London do you cover?
We're based in Clapham, SW2, and work on homes across London, including Wandsworth, Lambeth, Southwark, Kensington and Chelsea, Hammersmith and Fulham, Merton, Islington and Camden.