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The Ultimate Guide to Types of House Extensions

Explore the best house extension ideas for London homes. Costs, planning, real examples & expert tips to help you expand smartly and beautifully.

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Diagram showing types of house extensions in a typical London home, including rear, loft, side return, garage, and garden room extensions.

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Thinking of expanding your living space without the hassle of moving? A well-designed house extension can transform your home, add significant value, and give your family the extra room it needs to grow — especially in a city like London, where space is a premium.

In this ultimate guide to house extensions in London, we'll walk you through all the options available — from rear extensions to loft conversions, basement builds, and even stylish garden rooms. Whether you live in a classic Victorian terrace, a semi-detached home, or a modern build, there's a smart solution that fits your lifestyle and property type.

We'll also cover the planning process, cost considerations, design tips, and real-world examples from London homeowners who've made it work. Whether you're just exploring ideas or already sketching out plans, this guide is packed with everything you need to know about creating your dream house extension.

Introduction to House Extensions

Understanding the Need for Extensions

In a fast-paced city like London, where property prices soar and families outgrow their homes quicker than ever, house extensions have become a smart alternative to moving. Whether you're working from home, welcoming a new family member, or simply craving more space and light, extending your home can be a game-changer.

For many homeowners, especially those in desirable areas, moving is either too expensive or simply not worth the hassle. Instead, they're turning to extensions as a more affordable and personal way to tailor their homes to their needs. From side returns to lofts and garden rooms, the options are more diverse than ever.

Benefits of Extending Your Home

The most obvious benefit of a house extension is the additional space it creates — but there's more to it than that. Done right, an extension can enhance your quality of life, improve your home's flow, and boost its market value. In London, where square footage is gold, a smart extension can add anywhere from 10% to 25% to your property's value, according to property experts.

You also get the chance to modernise your layout, improve energy efficiency, and future-proof your home. Plus, since you're staying put, there's no need to say goodbye to the local school, your favourite bakery, or the neighbours you actually like.

All in all, a house extension is not just an upgrade — it's a lifestyle move, and often a long-term investment that pays off both financially and emotionally.

Single-Storey Extensions

Rear Extensions

Rear extensions are among the most popular choices for London homeowners, especially those with garden access. They allow you to push out the back of your home to create open-plan kitchens, dining areas, or multifunctional family spaces. These types of house extensions are especially effective in terraced and semi-detached homes, where rear-facing expansion can dramatically improve light and flow.

One of the biggest appeals of a rear extension is how it seamlessly connects indoor and outdoor living. Bi-fold or sliding doors are often used to bring in natural light and blur the lines between your kitchen and garden. For homeowners who love entertaining or want a more social family space, this layout is a dream.

Side Return Extensions

A side return extension utilises the narrow alleyway or dead space to the side of many Victorian and Edwardian properties. It may not seem like much, but gaining just 1.5 to 2 metres of width can completely change the way a kitchen or living area functions.

These extensions often involve removing part of the rear wall, replacing it with steel supports and glazed panels to flood the space with light. They're a perfect option for homeowners who want to extend without sacrificing too much garden space — a major concern in many parts of London.

Wrap-Around Extensions

For those looking for a more dramatic transformation, a wrap-around extension combines both a rear and side return extension. This L-shaped design maximises footprint while creating a stunning open-plan layout inside. It's especially popular in family homes where space for a large kitchen-diner, utility area, and lounging zone is needed.

Wrap-arounds do require more structural work and planning considerations, but they're one of the most impactful ways to reimagine how you use your home. Architects often play a big role in designing these to maintain flow, light, and proportion.

In short, single-storey extensions are one of the most flexible options for upgrading your home — whether you want subtle improvements or a full ground-floor transformation.

Double-Storey Extensions

Enhancing Vertical Space

Double-storey extensions are ideal for homeowners who want to add significant space without eating too much into their garden. By building upward rather than outward, you can double your square footage gain while keeping a relatively compact footprint. Typically, these extensions include a kitchen or living area downstairs, and an additional bedroom, bathroom, or office space above.

In London, where land is tight and every square meter counts, going up instead of out is often a smart move — especially for growing families who need extra rooms without compromising on outdoor space. These extensions are commonly built above existing ground floor additions or as part of a full redesign of the rear or side of a property.

Planning and Structural Considerations

Unlike most single-storey extensions, double-storey builds almost always require planning permission. Councils in London tend to be cautious about how these extensions affect neighbouring properties — particularly in terms of privacy, light loss, and overlooking. If you're in a conservation area or your home is listed, expect stricter rules and possibly additional architectural input.

Structurally, you'll also need to consider the foundation. Your existing home may require underpinning or reinforcement to support the extra weight of a second storey. This is where structural engineers come in, working alongside your architect to ensure safety and stability.

Although more expensive than single-storey options, double-storey house extensions offer a strong return on investment, especially in high-demand areas of London. They give you much more usable space and can be designed to blend in seamlessly with your existing property.

Loft Conversions

Dormer Conversions

Dormer loft conversions are the most popular type in London homes, especially in Victorian and Edwardian terraces. They involve extending the existing roof vertically to create a box-like structure, adding headroom and floor space. A dormer often allows for a full-sized bedroom, en-suite bathroom, or even a home office — all flooded with natural light through rear-facing windows or French doors with a Juliet balcony.

The beauty of a dormer is that it typically falls under permitted development rights, meaning you might not need full planning permission. It's a great choice for homeowners looking to add functional space without radically altering the roofline or street-facing aesthetic.

Mansard Conversions

Mansard conversions are more involved — they essentially rebuild one side of the roof to create an almost flat surface with a steep slope at the rear. This offers the maximum possible space and is often used in high-end conversions where homeowners want a full additional floor. They're common in central London, where maximizing property value is a top priority.

While they offer the most space, mansards almost always require planning permission due to the dramatic change in the roof shape and structure. But the payoff is worth it for those who want to create something truly transformative.

Hip-to-Gable Conversions

In semi-detached or end-of-terrace houses, hip-to-gable conversions are a clever way to make use of the sloped side of the roof (the “hip”) by building it up into a vertical wall (a “gable”). This opens up internal space and is often combined with a rear dormer to maximise room size.

They're popular in London suburbs where 1930s houses with hipped roofs are common, and they usually fall under permitted development.

Velux (Rooflight) Conversions

For those on a tighter budget — or looking for a home office or guest room without heavy construction — a Velux loft conversion might be the perfect fit. These involve adding skylights (Velux is just the brand name) to the existing roof without altering the shape or structure.

They require less time and disruption and usually don't need planning permission, but you'll need sufficient headroom and insulation to make the space truly comfortable. It's a great entry-level extension that works well in homes with generous loft height.

Loft conversions are not just practical — they're among the most cost-effective house extensions in London. They turn previously unused space into valuable real estate and can increase your home's value by up to 20%, all while staying within your existing footprint.

Basement Conversions

Creating Functional Underground Spaces

In high-end London postcodes where land is limited and building outward or upward isn't always an option, basement conversions offer a creative way to add serious square footage. Homeowners are transforming these below-ground spaces into home cinemas, gyms, wine cellars, utility rooms, or even full guest suites with private entrances.

Basement conversions are particularly popular in period townhouses, where maintaining the exterior aesthetic is essential but space is at a premium. They're also a great solution for homeowners who want to preserve garden space while still gaining an extra floor of usable space.

Waterproofing and Structural Integrity

Basements come with unique challenges that other house extensions don't — primarily, waterproofing and structural safety. The key to a successful conversion is a method called “tanking,” which involves sealing the walls and floor to prevent water ingress. Drainage systems and sump pumps are often installed to manage groundwater and protect your investment.

You'll also need to consider underpinning the existing foundations to allow for safe excavation — this isn't a light job. It requires experienced contractors, structural engineers, and often extensive liaison with your local council, especially in boroughs like Kensington & Chelsea or Westminster, where strict regulations are in place.

While basement conversions are among the most expensive types of house extensions (often £3,000+ per m²), they can add massive value to properties in prime locations — sometimes increasing a home's worth by hundreds of thousands of pounds.

If you're not afraid of a bit of complexity and want to maximise every inch of your property, a basement extension could be the bold move that takes your home to the next level — literally.

Conservatories and Orangeries

Conservatories

Conservatories have been a classic house extension option in the UK for decades. Built mainly from glass with a uPVC or aluminium frame, they're often attached to the rear of the property and used as sunrooms, play areas, or secondary lounges. For London homeowners looking for a cost-effective way to extend without major construction, a conservatory can be a great entry point.

Modern conservatories are far more advanced than their draughty predecessors. Today's designs use thermally efficient glazing, solid roof options, and better insulation, meaning they're usable year-round. And thanks to permitted development rights, many conservatories can be built without needing full planning permission — especially if they fall within size limits.

However, because they are still predominantly glass, heat retention in winter and overheating in summer can be concerns if not designed properly. Positioning, ventilation, and glazing choice are all critical to making a conservatory feel like a proper part of the home rather than just a bolt-on.

Orangeries

If you want something more solid and integrated than a conservatory, an orangery might be the better choice. Originally designed for growing citrus trees in the 17th century, modern orangeries are elegant hybrid extensions that combine brickwork with large glazed panels and often feature a lantern-style roof for light.

Orangeries strike a perfect balance between extension and feature room. They feel more like a natural continuation of your living space and can be used comfortably all year round. They're especially popular in more traditional or period properties, where a full-glass conservatory might look out of place.

Costs are higher than for a conservatory but still typically lower than a full rear extension. Plus, the visual impact they add — both inside and out — often makes them a favourite for homeowners wanting to increase space and wow factor at the same time.

Garage Conversions

Transforming Unused Garages

If your garage is more storage unit than parking space, you're not alone — and you might be sitting on prime real estate. Garage conversions are one of the simplest and most cost-effective house extension options, especially in suburban areas of London where many homes have integral or attached garages that are rarely used for cars.

These conversions typically involve upgrading insulation, replacing the garage door with a wall and window, and integrating the space into your existing floor plan. The result? A new bedroom, home office, gym, playroom, or even an en-suite guest suite — without expanding your home's footprint at all.

One of the best things about garage conversions is that they often fall under permitted development, meaning you won't need full planning permission — though you'll still need to meet building regulations. Plus, because the structural shell is already there, the construction time and cost are significantly lower than other extension types.

Insulation and Access Considerations

When converting a garage, insulation is key. These spaces weren't originally designed for living, so proper floor, wall, and roof insulation is essential to keep the room comfortable year-round. You'll also need to ensure there's adequate heating and ventilation, and if you're adding a bathroom or kitchen, that the plumbing can be extended easily.

Another big consideration is access. If your garage is detached or separated from the main living space, you'll need to plan how it connects — either with a new internal doorway or as a completely self-contained annexe. This can be a huge plus if you're planning to use it as a rental or guest space.

Garage conversions are a great way to breathe new life into dead space. With the right design, they can blend seamlessly into the rest of your home and boost both functionality and value.

Outbuildings and Garden Rooms

Detached Structures for Various Uses

With remote work becoming the norm and personal space at a premium, garden rooms and outbuildings have become a hot trend in London. These detached structures — often timber-framed and built at the end of the garden — offer a stylish, flexible solution for home offices, creative studios, gyms, or even guest accommodation.

One of the biggest appeals is separation. Unlike a rear or loft extension, a garden room gives you a dedicated space away from the main home, perfect for uninterrupted work or quiet downtime. It also offers lifestyle value — think yoga studio, art space, or even a teenage den.

These builds are usually highly insulated, fully powered, and can be tailored to match your aesthetic — from modern minimalist cubes to rustic cabins. And because they're technically “outbuildings,” they often fall under permitted development, provided they meet certain height, size, and usage restrictions.

Planning Permissions and Regulations

Garden rooms generally don't require planning permission if they are single-storey, under 2.5 metres high (if within 2m of a boundary), and not used as permanent living accommodation. However, if you're adding plumbing for a bathroom or planning to rent it out, you may need full planning approval and building regulations sign-off.

Also, if your property is in a conservation area or has listed status — which is fairly common in certain London boroughs — additional permissions will likely be required. Always check with your local authority before starting work.

Well-executed garden rooms can add value to your home, especially if they serve a clear, year-round function. And from a lifestyle perspective, having a peaceful, custom-built space just steps away from your back door is hard to beat.

Planning Permission and Building Regulations

Navigating the Legal Landscape

One of the biggest questions London homeowners ask before starting a house extension is: “Do I need planning permission?” The answer depends on the type, size, and location of the extension — but knowing the rules early can save you a lot of time, stress, and money.

Many common extensions, like single-storey rear additions or loft conversions, fall under what's called “permitted development rights.” This means you can go ahead without full planning permission, as long as you follow strict size and design limits. However, if your home is in a conservation area, is listed, or has had rights removed (common in central boroughs), you'll need full planning approval.

Planning rules also cover things like how the extension affects neighbours, especially when it comes to light, privacy, and the overall appearance of the street. If you're doing something more complex — like a double-storey build, basement excavation, or wraparound — assume you'll need planning consent.

Building Regulations Compliance

Even if you don't need planning permission, your extension will still need to meet UK Building Regulations. These ensure your extension is structurally sound, energy-efficient, fire-safe, and accessible.

Regulations cover things like foundations, insulation, drainage, ventilation, electrical safety, and even how stairs are designed. You'll usually work with a building control officer or an approved inspector, who will visit the site at key stages to sign off the work.

Skipping this step isn't just risky — it's illegal. Without proper sign-off, you might struggle to sell or remortgage the home later. The good news? A competent architect or builder will guide you through the whole process, so you're not left dealing with it alone.

When it comes to house extensions in London, planning and regulations can feel like red tape — but they're really there to protect your investment and your neighbours' peace of mind. Do it right from the start, and the rest of your project will be much smoother.

Cost Considerations

Budgeting for Your Extension

When it comes to house extensions, costs can vary wildly — especially in London, where materials, labour, and demand all run higher than the national average. On average, here's what you can expect to pay per square metre in 2025:

  • Single-storey extension: £2,000 – £3,200 per m²
  • Double-storey extension: £2,500 – £3,800 per m²
  • Loft conversion: £1,500 – £2,500 per m²
  • Basement conversion: £3,000 – £5,000+ per m²
  • Garage conversion: £1,200 – £2,000 per m²
  • Garden room: £15,000 – £40,000 total (depending on spec)

Keep in mind these are ballpark figures — your final cost will depend on location, size, finish level, access, and existing site conditions. In London, things like tight access, permit delays, or heritage property requirements can add to the bill.

Hidden Costs to Anticipate

It's easy to focus on the headline build cost, but there are a few “surprise” costs that homeowners often forget to budget for:

  • Planning and architect fees: Expect 8–15% of your project value.
  • Structural engineering: Around £1,000–£2,000 depending on complexity.
  • Party Wall Agreements: Required for many London builds, especially terraces.
  • VAT: 20% on most work, unless you qualify for exemptions (e.g. listed buildings).
  • Finishing costs: Flooring, lighting, kitchens, bathrooms — these add up quickly.
  • Temporary accommodation: If your home becomes unliveable during the build.

A good rule of thumb? Add 10–15% contingency on top of your estimated build cost to stay covered. It's better to be pleasantly surprised than caught off guard mid-project.

Being realistic from the start is key. The right extension will add value to your home — but only if the cost is managed wisely. Get quotes from multiple contractors, ask for breakdowns, and don't be afraid to question what's included (and what's not).

Choosing the Right Extension for Your Home

Assessing Your Needs and Property

Before you dive into floorplans or Pinterest boards, take a step back and ask: What do I actually need from this extension? Is it more living space? Another bedroom? A home office? Or just a better connection to the garden? Being crystal clear on the function will guide every decision after that.

Your property type matters too. A side return works wonders for Victorian terraces, while a loft conversion might be the best route for 1930s semis. Got a wide plot in a newer build? A rear or wraparound extension might be a better fit. Understanding your home's layout and limitations will help you avoid costly mistakes or wasted space.

Also consider the long-term: Will your family grow? Could you rent out part of the space later? Will this impact resale value or planning down the line? These aren't just add-ons — they shape the core of a good design.

Consulting with Professionals

Once you've nailed down your goals, speak to an architect or experienced design-and-build company. They'll help translate your wishlist into something structurally sound and planning-friendly. In many cases, they'll also spot opportunities you haven't thought of — like natural light tricks, flow improvements, or layout optimisations.

In London, where planning nuances can vary street by street, it's worth getting someone on board who knows your borough's planning quirks. The right professional can streamline permissions, liaise with surveyors, and help you avoid red tape.

A house extension is a big investment — not just financially, but in how you live. So take your time, plan with purpose, and don't just choose what looks good online. Choose what fits your home, your lifestyle, and your future.

Sustainability and Eco-Friendly Extensions

Incorporating Green Building Practices

In a city as environmentally conscious as London, many homeowners are now prioritising sustainability when extending their homes. From materials to energy systems, there are plenty of smart, eco-friendly choices that not only reduce your carbon footprint but can also lower your bills over time.

One of the simplest ways to make your house extension greener is through high-performance insulation and airtight construction. Combine this with double or triple glazing, and you'll instantly improve energy efficiency. Many architects are now incorporating passive solar design too — orienting extensions to make the most of natural light and heat throughout the day.

Material choice matters as well. Reclaimed timber, low-VOC paints, recycled insulation, and sustainably sourced bricks or cladding can all reduce environmental impact. Some homeowners even opt for green roofs, which help manage rainwater, improve insulation, and attract biodiversity.

Long-Term Benefits

While eco-friendly extensions may come with slightly higher upfront costs, they offer long-term payoffs: reduced heating bills, improved indoor air quality, and even higher property values. In fact, energy efficiency is becoming a major factor for buyers in the London property market — and a well-insulated extension can make your EPC rating more competitive.

Plus, with the UK pushing for net-zero carbon emissions, future regulations may demand higher energy standards. Building with sustainability in mind now means your home will already be ahead of the curve — saving you from future retrofits and keeping your home more resilient in the long run.

So whether you're planning a modest side return or a full double-storey build, thinking green isn't just a trend — it's a wise, future-proof investment.

Conclusion and Next Steps

Recap of Extension Options

Whether you're dreaming of an airy open-plan kitchen, a peaceful loft retreat, or a sleek home office at the bottom of the garden, there's a house extension that can bring your vision to life. In this guide, we've explored every major type — from single-storey builds and garage conversions to ambitious basements and eco-friendly garden rooms.

Each option has its own strengths, costs, and planning considerations — and the right choice depends entirely on your property, your budget, and your lifestyle. What works for a young couple in a Clapham terrace might not be right for a growing family in Ealing or a professional duo in Islington.

Planning Your Extension Journey

The key takeaway? Don't rush it. Start with a clear purpose, do your research, and speak to professionals who understand your local area and your long-term goals. An architect, builder, or design-and-build team can help turn ideas into a practical plan — and spot opportunities you might miss.

In London's ever-changing housing market, a thoughtful, well-executed extension can be a game-changer — giving you more space, more comfort, and more value. So whether you're ready to start drawing up plans or just daydreaming, you're already on the right track by learning what's possible.

From here, it's all about taking the next step — and turning that extra space into a better way of living.

Quick Takeaways

  • There are many types of house extensions in London, from side returns and lofts to basements and garden rooms — each suited to different needs and property types.
  • Single-storey and loft conversions are the most popular, offering strong ROI with relatively low disruption.
  • Double-storey and basement extensions offer the most space but come with higher costs and planning requirements.
  • Garage and garden room conversions are budget-friendly options that don't typically require full planning permission.
  • Planning permission and building regulations vary by borough — always check with your local authority before starting work.
  • Eco-friendly materials and energy-efficient design are becoming key features of modern house extensions.
  • Costs can range from £1,200 to £5,000+ per m² — always add a contingency budget of 10–15% to cover hidden expenses.

Frequently Asked Questions

1. What is the most cost-effective house extension in London?

Garage conversions and Velux loft conversions tend to be the most affordable. Since they often use existing structures and fall under permitted development, they're quicker and cheaper than full builds — typically starting around £1,200–£1,500 per m².

2. Do I need planning permission for a single-storey rear extension?

In many cases, no — single-storey rear extensions often fall under permitted development. However, size limits apply, and if you're in a conservation area or listed property, you'll likely need planning permission. Always check with your local council before proceeding.

3. How long does a typical house extension take in London?

Most extensions take between 8 to 16 weeks to build, depending on the size and complexity. Add time for planning, design, and approval — so from idea to completion, expect 4–6 months on average.

4. Will a house extension add value to my property?

Yes — a well-designed extension can add 10–25% to your home's value, especially in sought-after areas of London. Loft conversions, side returns, and kitchen extensions are particularly high-performing in terms of ROI.

5. What is the best house extension for a terraced house?

Side return and rear extensions are often ideal for terraced houses. They optimise narrow plots without sacrificing garden space. Loft conversions are also a great way to gain an extra bedroom or office without extending outward.

We'd Love to Hear from You!

Thinking about extending your London home? Already been through the process and have tips to share? We'd love to hear your thoughts, questions, or experiences in the comments below.

If you found this guide helpful, feel free to share it with friends or family who might be planning a house extension — it might just save them some serious time and stress!

Here's a question to get the conversation going: What's your dream extension — and what would you use the extra space for?

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