ExtensionsFebruary 26, 2025

Ultimate guide to House Extensions in the UK

A comprehensive guide covering everything you need to know about house extensions in the UK, including different types of extensions, planning permission, building regulations, costs, and finding the right builder.

Posted by

Gino S.

Types of House Extensions

Choosing the right type of extension is crucial. It depends on your budget, available space, planning restrictions, and your desired outcome. Here are the most common types of house extensions in the UK:

Single-Storey Rear Extension

This is one of the most popular extension types, extending the back of your house into the garden. It's often used to create a larger kitchen, dining area, or family room. Rear extensions can significantly increase living space and connect your home to the outdoors.

Pros: Relatively straightforward to build, adds significant living space, can improve connection to the garden.
Cons: Reduces garden space, may require planning permission.

Side Return Extension

Side return extensions utilize the often-unused space to the side of a property (typically found in Victorian and Edwardian terraced houses). They can be used to widen an existing room (like a kitchen) or create a new room altogether.

Pros: Makes use of often-wasted space, can significantly improve the layout of existing rooms.
Cons: May not be suitable for all property types, can impact natural light in neighboring properties (planning consideration).

Wrap-Around Extension

A combination of a rear and side return extension, a wrap-around extension extends around the side and rear of the property, creating a large, L-shaped space. This offers the most significant increase in living area.

Pros: Maximizes space, can dramatically transform the ground floor layout.
Cons: More expensive, likely to require planning permission, can significantly reduce garden space.

Double-Storey (Two-Storey) Extension

A double-storey extension adds space to both the ground and first floors, typically at the rear or side of the house. This can provide extra bedrooms, bathrooms, or larger living areas on both levels.

Pros: Adds significant space on two floors, can be more cost-effective per square meter than a single-storey extension.
Cons: More complex to build, almost always requires planning permission, can impact the overall appearance of the house.

Over-Structure Extension

This involves extending above an existing single-storey structure, such as a garage or kitchen. It's a great way to add an extra bedroom or bathroom without extending the footprint of the house.

Pros: Uses existing structure, can add valuable space without reducing garden area.
Cons: Requires careful structural assessment of the existing structure, may require strengthening of foundations.

Loft Conversion

While technically not an 'extension' in the sense of increasing the footprint, a loft conversion is a popular way to add living space by utilizing the existing roof space. It can create extra bedrooms, bathrooms, or a home office. Different types of loft conversions include:

Rooflight/Velux Conversion: The simplest and most cost-effective option, involving adding windows to the existing roofline.
Dormer Conversion: A structural extension that projects vertically from the roof slope, creating additional headroom and floor space.
Mansard Conversion: A more significant alteration to the roof structure, creating a near-vertical rear wall and a flatter roof. Offers the most additional space but is also the most expensive.
Hip-to-Gable Conversion: Extends the sloping 'hip' side of the roof outwards to create a vertical 'gable' wall, increasing internal space.

Pros: Adds living space without extending the footprint, can be very cost-effective, often doesn't require planning permission (under Permitted Development).
Cons: Headroom can be limited (depending on the type of conversion), may require staircase alterations.

Basement Conversion/Extension

Creating or expanding a basement can add significant living space, particularly in urban areas where extending outwards is limited. It can be used for a variety of purposes, from extra bedrooms and bathrooms to home cinemas and gyms.

Pros: Adds significant space without altering the external appearance of the house, can be ideal for creating self-contained accommodation.
Cons: Very expensive and complex to build, requires specialist expertise, can be disruptive.

Conservatory or Orangery

These glazed extensions add a light-filled space that connects the house to the garden. Conservatories are typically fully glazed, while orangeries have more brickwork and a lantern-style roof.

Pros: Creates a bright and airy space, can be less disruptive to build than other extensions.
Cons: Can be prone to temperature fluctuations (too hot in summer, too cold in winter), may require planning permission.

Garage Conversion

Converting an attached garage into living space is a relatively cost-effective way to gain extra room. It can be used for a variety of purposes, such as a home office, playroom, or extra bedroom.

Pros: Relatively inexpensive and straightforward, makes use of existing space.
Cons: Loss of garage space, may require upgrading of insulation and windows.

Planning Permission for Extensions

One of the first things you need to determine is whether your extension requires planning permission. Not all extensions need it, thanks to 'Permitted Development Rights,' but it's crucial to check before starting any work. Applying for planning permission typically involves submitting detailed drawings and plans to your local council. The council will assess your application based on factors such as:

Size and Height: There are limits on the size and height of extensions allowed under Permitted Development.
Impact on Neighbors: The council will consider the impact of your extension on neighboring properties, including loss of light, privacy, and overshadowing.
Appearance: The design of your extension should be in keeping with the existing property and the surrounding area.
Materials: The materials used should be appropriate for the location.
Location: If you live in a conservation area, National Park, Area of Outstanding Natural Beauty (AONB), or have a listed building, stricter rules apply.

You can find detailed guidance on planning permission on the government's Planning Portal website: Planning Portal.

Permitted Development Rights

Permitted Development Rights (PDR) allow certain types of extensions and alterations to be carried out without the need for full planning permission. However, these rights are subject to specific limits and conditions, which can be complex. It's *always* advisable to check with your local planning authority (LPA) before starting any work, even if you believe it falls under Permitted Development. You can apply for a Lawful Development Certificate (LDC) from your LPA, which provides formal confirmation that your proposed project is lawful.

Key limits and conditions for common types of extensions under Permitted Development (as of 2025 - these can change, so always check the latest guidance):

Single-Storey Rear Extensions: Limits on depth (e.g., 3 meters for terraced houses, 4 meters for detached houses), height (maximum 4 meters), and the proportion of the garden that can be covered.
Side Extensions: Limited to single-storey, maximum height of 4 meters, and width no more than half the width of the original house.
Two-Storey Extensions: Generally *not* permitted under PDR, unless they meet very specific criteria (e.g., not extending beyond the rear wall of the original house by more than 3 meters, and being at least 7 meters from the rear boundary).
Loft Conversions: Often permitted, but subject to volume limits (e.g., 40 cubic meters for terraced houses, 50 cubic meters for detached and semi-detached houses) and restrictions on dormer windows.

Building Regulations

Regardless of whether your extension needs planning permission, it *must* comply with Building Regulations. These regulations set standards for the design and construction of buildings to ensure the health and safety of people in and around them. Building Regulations cover aspects such as:

Structure: Ensuring the extension is structurally sound.
Fire Safety: Including escape routes, fire-resistant materials, and smoke alarms.
Insulation: Meeting minimum energy efficiency standards.
Ventilation: Providing adequate ventilation to prevent condensation and ensure good air quality.
Drainage: Ensuring proper drainage of wastewater.
Electrical Safety: Meeting electrical safety standards.
Glazing: Using safety glass in critical locations.

You'll need to submit a Building Regulations application to your local authority Building Control department (or use an Approved Inspector). Inspections will be carried out at various stages of the build to ensure compliance. Upon completion, you'll receive a completion certificate, which is essential when selling your property.

The Party Wall Act

If your extension involves work on or near a shared boundary (party wall) with a neighbor, you'll need to comply with the Party Wall Act 1996. This act is designed to prevent and resolve disputes related to party walls, boundary walls, and excavations near neighboring buildings.

You must serve a Party Wall Notice on your affected neighbors at least two months before starting work. The notice should describe the proposed work and include plans. Your neighbors can either consent to the work, dissent (requiring a Party Wall Surveyor to be appointed), or agree with conditions. It is always a very good idea to speak with your neighbors before serving formal notices.

House Extension Costs

The cost of a house extension in the UK can vary significantly depending on numerous factors, including:

Type and Size of Extension: A small single-storey extension will be much cheaper than a large two-storey extension or a basement conversion.
Location: Labor costs and material prices can vary across the UK, with London and the South East generally being more expensive.
Materials and Finishes: Choosing high-end materials and finishes will significantly increase the cost.
Complexity of the Build: Factors like sloping sites, difficult access, and complex designs will add to the cost.
Professional Fees: Architect fees, structural engineer fees, planning application fees, Building Control fees, and Party Wall Surveyor fees.

As a *very rough* guide (as of 2025, and these prices can fluctuate significantly):

Single-Storey Extension: £1,500 - £3,000+ per square meter.
Two-Storey Extension: £1,300 - £3,000+ per square meter.
Loft Conversion: £1,500 - £2,500+ per square meter (depending on the type of conversion – rooflight conversions are cheapest, mansard conversions are most expensive).
Basement Conversion: £3,000 - £5,000+ per square meter (basement conversions are significantly more expensive due to the complexity of excavation and waterproofing).
Garage Conversion: £1,000 - £2,000+ per square meter.

These figures are *exclusive* of VAT (Value Added Tax), professional fees, and fixtures/fittings. It is essential to get detailed quotes from builders for your specific project.

Finding a Reputable Builder

Finding a trustworthy and competent builder is arguably the most critical step in a successful extension project. Here's how to find the right one:

Get Recommendations: Ask friends, family, neighbors, and colleagues for recommendations. Personal referrals are often the best starting point.
Online Platforms: Use reputable online platforms like MyBuilder, Checkatrade, TrustATrader, and Federation of Master Builders (FMB) to find vetted and reviewed builders in your area.
Check References: Always ask for and *follow up* on references from previous clients. Speak to them directly about their experience with the builder.
View Previous Work: If possible, visit previous projects completed by the builder to assess the quality of their workmanship.
Check Insurance and Qualifications: Ensure the builder has adequate public liability insurance and any relevant qualifications (e.g., for gas or electrical work). Membership of a trade association like the FMB can also be a good indicator of professionalism.
Get Detailed Quotes: Obtain written quotes from at least three different builders. The quotes should be detailed and itemized, breaking down the costs of labor, materials, and any other expenses. Beware of quotes that are significantly lower than others, as this could indicate corner-cutting.
Use a Contract: Always have a written contract with your builder. The contract should clearly outline the scope of work, payment schedule, timelines, and dispute resolution procedures. The JCT (Joint Contracts Tribunal) offers standard form contracts for home building projects.
Trust your Gut: If you have any doubts or concerns about a builder, don't hire them. It's essential to have a good working relationship and feel comfortable with the person you choose.
Read here our guide on how to choose a bathroom fitter. While the article is geared towards bathroom renovation companies, the same principles apply. We will update this link to a more targeted article once it is up.

Design Considerations

Thoughtful design is key to a successful extension. Consider the following:

Purpose: What will the new space be used for? How will it integrate with the existing house?
Natural Light: Maximize natural light through carefully positioned windows, skylights, and glazed doors.
Flow: Ensure a good flow between the existing house and the new extension. Avoid creating awkward or unusable spaces.
Materials: Choose materials that complement the existing property and are appropriate for the location.
Sustainability: Consider incorporating sustainable design features, such as high levels of insulation, energy-efficient windows, and renewable energy sources.
Future-Proofing: Think about your future needs and how the extension could be adapted over time.

Consider hiring an architect or architectural designer. They can help you develop a design that meets your needs, maximizes space, and complies with planning and building regulations. While adding to the initial cost, a well-designed extension can add significantly more value to your property.

Project Management Tips

Even with a good builder, staying involved in the project is crucial. Here are some project management tips:

Regular Communication: Maintain regular communication with your builder. Schedule site meetings to discuss progress and address any issues.
Keep Records: Keep detailed records of all communication, payments, and changes to the project.
Be Prepared for Disruptions: Building work is inherently disruptive. Be prepared for noise, dust, and limited access to certain areas of your home.
Make Decisions Promptly: Delays in decision-making can hold up the project and increase costs. Be prepared to make decisions quickly when required.
Contingency Fund: Have a contingency fund (typically 10-20% of the total budget) to cover any unexpected costs.
Snagging: At the end of the project, create a snagging list of any minor defects or unfinished work that needs to be addressed.

Conclusion: Extending Your Home Successfully

Extending your home can be a complex but ultimately rewarding project. By carefully planning, choosing the right type of extension, understanding the relevant regulations, finding a reputable builder, and staying actively involved throughout the process, you can successfully create the extra space you need and add significant value to your property. Remember to do your research, get professional advice, and be prepared for some challenges along the way. Good luck!