House extensions – Single storey extension
London architect guide
Planning a single storey extension in London?
Our homeowner guide covers everything you need to know — from how much a single storey extension costs and whether you need planning permission, to how long it takes, how to maximise value, and how to get started. Written by expert London residential architects, this guide will help you make informed decisions and avoid costly mistakes on your home extension project.
A well-designed single storey extension can completely transform your London home. Whether you want a spacious kitchen-diner, a light-filled family room, or better access to the garden, extending at ground floor level often provides the most cost-effective and planning-friendly way to improve how you live.
At GOAStudio architects we specialise in single storey extensions tailored to your home, your lifestyle, and your local planning context.
We’ve worked across nearly every London borough, including with listed buildings and homes in conservation areas, helping homeowners make the most of what’s possible, both in terms of space and value added.
FOR ADDITIONAL ADVICE SEE THE FOLLOWING RESOURCES FOR YOUR HOME PROJECT
Royal Institute of British Architects (RIBA)
- Do I need an architect for my extension or home project?
- Why work with an architect?
- How do architects calculate their fees?
Planning Portal
Single storey rear house extension ideas photo gallery GOAStudio architects
Lewisham SE13 Rear kitchen extension Outside in
Hammersmith architects house extension and renovation Rear elevation
Arnos Grove N11 bungalow house extension green renovation by GOAStudio architects Rear elevation
Top 10 Tips Before You Start Your Single Storey Extension
- Be clear on your goals: What’s driving the project — lifestyle upgrade, space need, or resale?
- Decide early how involved you want to be during construction.
- Prepare a Pinterest or inspiration board — it helps us understand your likes and dislikes.
- Think about natural light first, then layout.
- Talk to neighbours early, especially if boundary walls are involved.
- Keep a contingency budget for surprises, especially in older homes.
- Consider sustainability: better insulation and energy conservation measures often pay off quickly.
- Don’t overextend. Balance space gain with cost, proportions, and garden loss.
- Phase the works if needed.
- Ask questions. A good architect won’t just design but they’ll guide and inform every step.
GOAStudio London residential architecture
George Omalianakis, BA (Hons) B.Arch Pg Dip Environmental Design.
Chartered RIBA architect and ARB registered.
RIBA Conservation Registrant specialism in conservation areas, period and Listed buildings.
Residential expert contributor for magazines including Which? magazine and Ideal Home.
Last reviewed by George Omalianakis for GOAStudio: August 2026
How much does a single storey extension cost in London?
In London, the typical construction cost for a single storey extension ranges from £2,500 to £3,500 per square metre, depending on materials, layout complexity, and site conditions.
You’ll also need to account for VAT, planning and building regulation fees, architectural and structural design fees, fixtures, fittings, and a contingency of around 10–15%.
For example, a 4x5m (20m²) rear extension could cost £50,000–£70,000+ before finishes and VAT. A more complex side-return wraparound with steelwork and bespoke glazing might reach £100,000+.
During the design development stage we will help you shape the brief around a realistic budget.
Your final spend will also depend on the level of finish you’re aiming for.
High-end kitchen fittings, bespoke glazing, and premium flooring can significantly affect the final figure.
At GOAStudio architects we help you break down these allowances early to avoid budget surprises. We also provide guidance on phasing which can help manage cashflow.
Do I need planning permission for a single storey extension?
Not always. Many single storey extensions fall under Permitted Development Rights (PD), which means you may not need full planning permission.
But PD doesn’t apply in all cases especially in conservation areas, listed homes, flats and converted buildings.
Even when PD applies, we often advise obtaining a Lawful Development Certificate to confirm that your single storey extension complies with the relevant requirements. If you’re unsure whether your home qualifies for PD, we can carry out a quick desktop planning review. Where planning permission is needed, GOAStudio architects will manage the entire process including drawings, statements, and liaising with your local council.
A common misconception is that small extensions are always ‘automatic approvals’.
In fact, local design policies, neighbour objections, and site-specific constraints like trees, light angles, or drainage often come into play. This is where our experience across 20+ London boroughs comes in.
We anticipate what’s likely to be supported and help build the strongest case possible before submission.
How long does it take to build a single storey extension?
Most single storey extensions take around 3–5 months to construct once on site.
The full project timeline includes:
– 4–6 weeks for measured survey and design development
– 8 weeks for planning approval (if required)
– 4–6 weeks for technical design, structural input, and builder quotes
You’ll also need to factor in Party Wall agreements (if required), which can add 2–6 weeks, and builder availability — quality contractors often book 2–4 months ahead.
We’ll coordinate these timelines and help you plan your project from the beginning.
Clients often ask if they can live in the house while works take place. The short answer is: yes, but it depends.
If your project affects your kitchen, heating or water access, you’ll need a temporary setup. We advise early on how to plan for this including cost-effective temporary kitchens and protective partitions to separate construction from living space.
Do I need an architect for a single storey extension?
You’re not legally required to hire an architect, but a single storey extension done without one often leads to compromised layouts, missed opportunities, or increased costs down the line.
An architect will:
– Maximise light, flow and functionality
– Design the space around how you live
– Navigate planning and building regulations
– Coordinate with structural engineers and builders
We also ensure your extension has the potential to meet Building Regulations, integrates thermal performance and ventilation, and provides comfort around how you live. This isn’t just about compliance — it’s about designing a home that feels right year-round.
How big can a single storey extension be? Does the 45-degree rule apply?
Yes. Many London planning authorities use the 45-degree rule to assess how your single storey extension might affect neighbouring homes. This guideline can impact depth, height, and position, particularly near shared boundaries.
Under Permitted Development you typically get approvals for the following:
– Terraced homes: up to 3m deep
– Detached homes: up to 4m deep
– Max height: 3m (flat roof) or 4m (pitched roof)
In some cases, we may recommend applying for full planning permission to go beyond these limits. We’ll always advise on the risks and rewards so you can make an informed decision.
During the design development stage we might seek the assistance of consultations to prepare daylight / sunlight path assessments, neighbour context studies, and light modelling where needed to demonstrate minimal impact.
This technical approach helps reinforce our planning application and gives you peace of mind that what’s proposed is both ambitious and achievable.
How much do architects charge for a single storey extension?
Architect fees vary depending on scope. Most architects offer:
– Fixed fees per stage (design, planning, technical, etc.)
– Percentage of build cost (typically 8–12%)
– Hourly or daily rates for consultations or focused input
Our fees are transparent and flexible. They typically include:
– Design development and layout proposals
– Planning application drawings and documents
– Coordination with structural engineers
– Support with approvals and contractor quotes
You can start with a standalone 2-hour home consultation to explore options with no obligation to proceed.
Beyond core design, planning, and technical drawings, we can also assist with contractor selection, tender reviews, site visits during construction, and design management support during the construction stage. These additional services are optional, but many clients choose them to ensure smooth delivery and consistent design intent from start to finish.
How much value does a single storey extension add?
A well-designed single storey extension can increase your home’s value by £50,000 to £150,000+, depending on location, layout and finish quality.
But value goes beyond resale. A great extension enhances:
– The way your home flows and feels
– Natural light and garden connection
– Adaptability for future needs
Local estate agents regularly highlight how open-plan kitchen extensions and family spaces rank at the top of buyers’ wish lists. Even if you’re not planning to sell soon, you’re investing in a better way of living now and for years to come.
We also advise on smart layout improvements that boost lifestyle quality and long-term flexibility. For example, a utility room, a flexible workspace zone, or improved insulation can set your home apart while keeping future resale front of mind.
Request a free Feasibility Review
If you're not quite sure what’s possible, or whether now’s the right time, we can help you make an informed start.
Send over your address, a few photos, and a short outline of what you're hoping to achieve.
We’ll take a look at your site context, planning history, and potential constraints and respond with early advice tailored to your home and circumstances.
Email us with the subject “Feasibility Review” or send us your information through our Contact us page.
Book a Home Consultation
It is the ideal first step if you are planning works to your home or if you are in the middle of purchasing a property in need of renovation.
George will visit the property to understand its character, how you use the space day to day, and offer advice on all relevant design and other matters.
You will come away with a clear sense of your next steps and greater confidence to make informed decisions. The consultation (2hrs, £250 +VAT) is a standalone service with no obligation to proceed.
Visit our Contact us page to book.
Not sure where to start with your renovation or extension?
Read this before you meet an architect, speak to a builder or spend money on drawings.
This free, architect-prepared guide walks you through the 15 essential questions every homeowner should ask before starting a project.
"Should we renovate, extend… or walk away?
15 Questions every London homeowner must ask before starting a project to include homes in Conservation Areas and Listed Buildings."
Whether you're planning a modest rear extension or major alterations to a listed home, it will help you avoid expensive mistakes and give you clarity on what’s possible for your property. Includes guidance on:
Planning approvals. Conservation areas.
Timelines and costs. Appointments you need to make.
Design and sustainability options.
When to press ahead and when to walk away
We provide architectural services for residential projects in the following London Boroughs:
Barnet, Camden, Enfield, Hackney, Hammersmith and Fulham, Haringey, Islington, Kensington and Chelsea, Lambeth, Lewisham, Newham, Tower Hamlets, Waltham Forest, Wandsworth, Westminster
We specialise in
- Greener homes
- Retrofit and energy efficiency for older and traditional buildings
- Conservation areas
- Listed Buildings
- Homeowner architectural services
- Property developments architectural services
GOAStudio London residential architecture limited.
86-90 Paul Street, EC2A 4NE, Hackney
Chestnut Avenue South, E17 9EJ, Waltham Forest
t: 0203 984 3005
