House Extension Guide

Thinking about a house extension?

This article will look at the different house extension types, including the labour and supply costs that you can expect to pay. It will also consider the timeframes for different extensions, the choice of design ideas and the average cost of house extensions.

We will discuss the advantages and disadvantages of building your own home extension and what questions to ask when considering adding an extension to your home.

With so many different types of house extension to choose from, the process of matching the right extension to not only your property but also to the needs of your household is not easy.

This article should help you decide which type of extension is best for your house and will best serve the needs of your family.

What Is a House Extension?

As there are so many different ways of extending a property, it can be confusing as to what constitutes a house extension. Some are called conversions, so does this qualify as an extension? And is a garage conversion an extension?

An extension is part of a property that was not part of the house's original construction and may include elements that are removed or replaced. A loft conversion is an extension as it is added later as is a conservatory or a side return extension that was not part of the original house plan.

There are many reasons why someone would want or need to extend their home. One of the most common reasons is because your family is growing in number or size. The need for extra bedrooms is probably the most often cited reason for a home extension.

Whether this is to accommodate new family members or because children have outgrown their bedroom and need a bigger space, a property extension is often preferable to moving to a larger house. Even a small house extension can create a better living environment for your family.

In recent times a large proportion of the working population have had to adjust to working from home and are now having to find a suitable space in their house to do this.

It may mean that a garage is converted to a home office or a loft conversion is installed to enable someone to have space away from the rest of the household to work undisturbed. This more recent development has been driven by necessity more than personal choice but is a valid reason for having a home extension.

Types of House Extensions

The house extension cost will depend on the type of extension or conversion you opt for. This choice will also obviously depend on the reason for the property being extended. While there are no cheap home extensions, the price you pay will be influenced by the kind of extension you choose. The planning limits in this guide are for England, so if you live in Wales, Scotland or Northern Ireland, check with your local council as the rules differ.

Side Extension

A side extension will work for most properties, whether detached, semi-detached or terraced, with some limitation on space for a terraced home.

It is one of the most straightforward extensions to build, and there are many side extension ideas to choose from. A two-storey side extension will always need planning permission.

Pros

• ✔ Potentially the easiest and one of the least expensive extension options.
• ✔ It can also be done on a terraced home in most cases as a side return extension.
• ✔ Increases the amount of living space, particularly for kitchen/diners.

Cons

• ✖ Will typically only be single storey with a maximum height of 4 metres under permitted development.
• ✖ May not add to the value of the property as much as a loft conversion or similar.
• ✖ The loss of outside space or garden may reduce the saleability of the house in future.

Rear Extension

For rear extension ideas adding additional functional living space is perhaps the most common. The most popular room to install in this type of extension is a kitchen or kitchen/diner, often with direct access to the garden. Rear extension ideas also include conservatories, sun rooms or enlarged living rooms.

Pros

• ✔ Possibility to extend by 8 metres for a detached property or 6 metres for an attached house when building a single-storey extension under the larger home extension scheme.
• ✔ An existing kitchen can be enlarged and transformed into a modern and light-filled kitchen/diner.
• ✔ A rear extension can blend the house with the garden making it an enjoyable and sociable space.

Cons

• ✖ Under permitted development, a double-storey rear extension can only extend 3 metres and must stay at least 7 metres from your rear boundary, although planning permission may allow you to go further.
• ✖ Rear extensions are typically more expensive to build than a side extension.
• ✖ The loss of outside space such as a garden or terrace should be considered.

Double-Storey Extension

This type of extension involves building a ground floor and first floor addition to a property. Planning rules for two-storey extensions have not changed, but some homes in England can now add extra storeys above the existing property. This type of upward extension may be allowed through prior approval from the local council.

Pros

• ✔ Two-storey extensions are not that much more expensive than single-storey extensions.
• ✔ Functional rooms such as kitchens and bathrooms can be added as well as bedrooms.
• ✔ Will typically add value to a property with the increase in bedrooms and habitable space.

Cons

• ✖ In many cases you will need planning permission for a two-storey extension.
• ✖ Objections from close neighbours may be more likely with a potential loss of light, raising issues.
• ✖ A rear double-storey extension will potentially take up a large portion of outside space.

Multi-Storey Extension

A multi-storey house extension involves adding more than one storey to a property and will most certainly require planning permission in the majority of cases. Under permitted development, an extension with more than one storey can only go at the back of the house, no more than 3 metres deep and at least 7 metres from the rear boundary.

Pros

• ✔ Allows greater expansion and use of space within the property.
• ✔ By increasing the habitable space, the value of the house should be increased.
• ✔ You can future proof your house by adding rooms that may be needed later, such as larger bedrooms or separate accommodation for an elderly relative.

Cons

• ✖ More expensive with materials, labour, and the cost of applying for planning permission.
• ✖ Professional contractors will be necessary for a project of this size, not a self-build option.
• ✖ Planning permission will be required for anything that goes beyond the size and position limits of permitted development.

Bungalow Extension

There are many bungalow extension ideas to choose from. A bungalow is an ideal property for a loft conversion, side or rear extension. Typically, pre-1960s bungalows have large footprints, and many are sited on good-sized plots.

Pros

• ✔ An extension such as a loft conversion can almost double the amount of habitable space of a bungalow.
• ✔ Most bungalows have good-sized gardens, which will allow for a side or rear extension.
• ✔ Planning permission, if needed, is often given to allow older properties to be redeveloped in line with local planning policies.

Cons

• ✖ Under permitted development, you're limited to a loft conversion or single-storey side or rear extension, and building an extra storey on top will need prior approval or full planning permission.
• ✖ To stay within permitted development, the exterior materials must match the look of the existing house, so a more modern, contrasting design will need planning permission.
• ✖ Side or rear extensions can use up a lot of garden space which can impact the re-saleability of the house.

Loft Conversion

This is one of the most popular types of extension as most properties have a loft that can be converted. It also leaves outside space and garden untouched, adding to the overall appeal of the property.

Pros

• ✔ Increases the habitable space of the property without compromising the outside space or garden.
• ✔ Most lofts can be converted, and typically you can add at least one bedroom and a bathroom.
• ✔ A loft conversion with a double bedroom and bathroom can add up to 24% to the value of a three-bedroom, one-bathroom home.

Cons

• ✖ Valuable storage space is lost, especially if you have nowhere else to store little-used items.
• ✖ Without applying for planning permission, the conversion will be limited to the constraints of permitted development and the height of the roof.
• ✖ A loft extension typically only allows for a bedroom, bathroom or home office and cannot normally facilitate a larger kitchen, unlike a side or rear extension.

Garage Conversion

If you require additional living space and have a garage that is only used for storage, then a garage conversion is an ideal solution. This kind of extension can comprise additional bedrooms, living areas or even a larger kitchen or bathroom.

Pros

• ✔ Much cheaper than building an extension or loft conversion.
• ✔ Most garage conversions can go ahead without planning permission, as long as the work is internal and doesn't make the building any bigger.
• ✔ Minimum disruption during construction work unless a full ground floor remodelling is included.

Cons

• ✖ You may need planning permission if the garage will become a separate home, or if your property's permitted development rights have been removed.
• ✖ If you do use the garage for parking your car, then you will need to consider where your car will be stored, as this may affect your car insurance.
• ✖ The space available for development will be limited to the footprint of the garage.

Conservatory

Rear extension ideas include this type of house extension, which has acquired a somewhat undeserved bad reputation as an old-fashioned and underused addition to a home. While it is true that some older conservatories were little used in all but the sunniest weather, modern conservatories can be both practical and stylish.

Pros

• ✔ Can be added to your home under permitted development.
• ✔ Modern conservatories typically have underfloor heating and electrically operated roof lights to control the interior temperature.
• ✔ Available in many different styles and designs to complement most homes.

Cons

• ✖ Conservatories have come a long way in style, design and functionality but are still viewed by many as outdated and pointless.
• ✖ Limited in their use unless they are built to meet the standards needed for a kitchen or bathroom.
• ✖ A cheap or badly installed conservatory can detract from the value of a property.

Basement Conversion

Not everyone will have the option to convert a basement, but those who do can create a whole new level in their home with various potential uses. As part of a multi-storey house extension, a basement can significantly increase the value of a property where land is at a premium, such as London or other large cities.

Pros

• ✔ Almost any type of room can be incorporated into a basement conversion.
• ✔ In areas where land is at a premium like London, extending your home into the basement is an ideal way to increase the habitable space.
• ✔ Can add to the value of the property, particularly in areas such as London or other major cities.

Cons

• ✖ The financial outlay should be weighed against property values in the area.
• ✖ Planning permission may be needed if you add a lightwell, alter the outside of the house, or use the space as a separate home or for a business.
• ✖ If underpinning or digging out the floor is necessary, then the cost will be almost double.

House Extension Ideas

There are countless house extension ideas with only space, budget, planning rules and building regulations placing limitations on what you can achieve.

How much room, time, money, and development allowance you have will play a part in your house extension plans, but there are so many options that you will not be left without ideas.

Extending & Remodelling

Perhaps the first consideration when planning an extension is how to blend it into your existing house. If you have purchased an older property with lots of character, you will want to decide how to incorporate an extension into the current house.

Or you may want to re-purpose existing rooms in the house and blend them into the extension, for example, by merging an unused dining room with a new reception room to create a larger living space.

Kitchen/Diner

One of the most popular house extension ideas is to add a kitchen extension, creating a larger kitchen/dining area. Large, glazed doors such as bi-folds and roof lanterns on an extension can make a kitchen/diner blend seamlessly into the garden or outside space. This is a popular idea for single-storey rear extensions.

Upside-Down Living

An unusual idea but one that works very well in some properties is to add an extension to a property but have the living space on the top floor and the bedrooms on the ground floor. This house extension idea allows homes that have good views from upstairs to be enjoyed during the day.

Conservatory/Orangery

Installing a conservatory or orangery can add beautiful living space to a home and can be creatively linked to the garden through the use of glazing, pergolas, or lighting.

Although not the most popular of rear or side extension ideas, conservatories can be used as functional space or an additional living room, depending on your needs.

Complement or Contrast?

Adding an extension to an existing property offers the choice of whether to be decorated in line with the original design or contrast with a completely different look.

For example, a stone-built cottage with a glass and metal constructed extension or a bolted-on design where an extension is linked to the original building via a glass corridor. A contrasting design like this will need planning permission, as extensions built under permitted development must have a similar appearance to the original house.

Small house extensions will not pose too much of an issue, but two-storey extensions will need careful consideration on whether to complement or contrast.

What Are the Pros and Cons of a House Extension?

Deciding to add an extension to your home is a big step and should be considered with care. Not only do you need to think about the cost of building an extension but also furnishing it, the disruption to daily life and what impact it may have on your neighbours.

Here are some pros and cons of a house extension which you need to consider.

Pros

Improve Don't Move

By extending your house, you will be adding to the existing living space and giving your family more room. It may also mean there is no need to move with all the upheaval, disruption, and cost that a house move involves.

This is especially true when you have children as it removes the need to change schools or leave friends behind, both of which can be unsettling.

Adding Value

An extension can and should increase the value of your home. Extra bedrooms in particular can make a big difference, with Nationwide's 2025 research showing that an additional double bedroom can add around 13% to 17% to a two-bedroom home and 10% to 13% to a three-bedroom home.

Increased living space and a well-designed extension are always appealing to potential buyers.

Future-Proofing

For those living in two-storey homes who do not wish to move, adding a ground floor extension is a good way to future proof for decreased mobility later in life.

By having a downstairs bedroom and bathroom, problems with access will be avoided while still having available accommodation for visiting families or friends.

Cons

Overspending

When considering an extension of any kind to your home, you need to ensure that you are not overspending and that you will get a return on your investment. Not just in terms of additional living space, but you should have increased its value when it comes to selling the house.

Before deciding on the size and standard of finish for your extension, you should research what the ceiling price on your type of property is for the area. If you spend too much on the extension, there is a risk that you will not recoup the outlay.

Disruption

Having construction work is always disruptive, whether it is a loft conversion or a full wrap-around extension.

The question of whether you should move out during the works will depend on your individual family situation and your budget. Those with small children, elderly relatives or pets may want to avoid living with the noise, dust, and upheaval of major construction work if the budget allows.

How Much Does a House Extension Cost?

The average cost of a house extension will depend on several factors:

Extension Types

• Side Extension Costs — Potentially the easiest and one of the least expensive extension options.
• Single-Storey Extension Costs — One of the most straightforward projects, taking up to 12 weeks, depending on size.
• Double-Storey Extension Costs — The cost of house extensions with two storeys is not that much more than a single-storey extension with both needing foundations and a roof which are the most expensive elements of the build.
• Multi-Storey Extension Costs — More expensive with materials, labour, and the cost of applying for planning permission.

Additional Jobs

• Skip Hire Costs — The cost will vary depending on where you live in the UK, the size of the skip, and the duration of the hire.
• Carpet Laying Costs — Price depends on the carpet quality and the room size.
• Wood Flooring Costs — Prices vary depending on the type of wood used. This could be oak, pine, maple, or engineered wood.
• Kitchen Remodelling Costs — The size of the room, the quality of fittings, and how much of the existing kitchen needs to be replaced will all affect the cost.
• Room Decoration Costs — Costs depend on the size of the extension and the area you live in.

How to Build a House Extension

The process of building an addition to your home, whether that is a loft extension or a side return extension, will differ according to the type of extension, size and specification.

Planning & Preparation

• House Extension Plans — Decide the size, design, and layout of your extension. A two-storey side extension will involve more thought and planning than a garage conversion. Architect fees will vary according to where you live.
• Materials — The contractor will calculate the type and amount of materials needed and arrange deliveries with local building material suppliers.
• Planning Permission — If you require planning permission, this will take between 8 and 13 weeks, depending on the complexity of the plans. This will depend on how large the extension will be, the area you live in, and any restrictions, such as living in a conservation or other designated area.
• Building Regulations Approval — Your extension will need Building Regulations approval, even if planning permission is not required. You can arrange this through your local council or an approved private building control provider.

Building the Extension

• Foundations Laid — Foundations will be laid first, followed by the walls of the extension being built.
• Roof Structure and Windows — When walls are complete, the roof structure will be built and the windows and doors installed, making the extension weather-tight.
• Insulation Fitted — Insulation should be fitted in the floor, roof, and walls to meet Building Regulations.
• Electrics, Plumbing and Plastering — First fix electrics and plumbing will be completed, followed by plasterboarding and plastering. Once the plaster has dried, second fixing includes electrics, plumbing, and carpentry.
• Decorating — Decorating and flooring should be completed before any final floor covering is laid to protect it.

Post-Construction

• Building Control Inspections — Various stages of the build will need to be inspected by a building control officer to ensure compliance with Building Regulations.
• Completion Certificate — Will be issued to confirm that the work meets all Building Regulations. Keep this safe, as it will be needed if you ever sell the property.

DIY or Professional Contractor

There are various stages involved in building a house extension and many areas of expertise needed, including electrics, plumbing, and plastering. Any wiring must meet Part P of the Building Regulations, so it will need to be done by an electrician registered with a competent person scheme or checked by building control.

While DIY may seem money-saving, work that doesn't meet standards and needs remedying is an expensive route. Projects will also take longer without two or three trades on site simultaneously.

As a result, most homeowners choose to hire a professional. You can request several quotes from house extension builders near you, using MyJobQuote. It's fast, free, and there is no obligation to go ahead.

How Long Does It Take to Build a Home Extension?

Different types of house extensions will vary in the time they take to complete. Various factors such as size, design and the need for planning permission will impact the timeframe for a home extension.

Loft Extension

There are several types of loft conversion, and they can vary from 6 weeks for a rooflight conversion to 14 weeks for a mansard style conversion. The complexity of the build, as well as the need for any necessary planning permission, can influence the timescale for a loft extension.

Single-Storey Extension

A side or rear single-storey extension is one of the most straightforward projects to increase the habitable space of your home. This work should take between 8 and 10 weeks, depending on size and allowing for good weather conditions to complete the build.

Double-Storey Extension

Two-storey extensions are going to take a bit longer to finish. However, there are many complex elements that are similar to a single-storey extension, including foundations and the roof. However, the second storey will add to the timescale, and this can mean that a two-storey side extension can take between 10 and 14 weeks.

Garage Conversion

There are many advantages to converting your garage, such as not needing planning permission, minimal disruption to daily living and no need for scaffolding. Another advantage is that a garage conversion should take no more than 6 weeks to complete.

Conservatory

Building a conservatory is something that specialist contractors and companies normally undertake. The average installation time for a conservatory or orangery is 3 to 4 weeks, although this can vary according to the size and complexity of the design.

Basement Conversions

These are not the most common house extensions but are popular in London properties where space is at a premium and homeowners can afford this type of conversion. However, due to the nature of the construction work, it can take a lot longer than normal house extensions.

Issues such as access, waterproofing and proximity to underground services can have a severe impact on the timescale of a basement conversion which can take anything from 8 to 20 weeks.

Building Regulations & Planning Permission for House Extensions

Not all house extensions need planning permission, but most will need Building Regulations approval. A small conservatory is one of the few exceptions, as long as it's kept separate from the main house.

Building Regulations to Be Followed

There are different Building Regulations that need to be adhered to according to the type of house extension being built. The majority of extensions will need to adhere to Building Regulations for the following:

• Doors and windows
• Drainage
• Electrics
• External walls
• Kitchens and bathrooms
• Internal walls
• Roofs

To ensure that your house extension follows the necessary regulations, a building control officer will visit your site at appropriate times during construction to inspect and check that this is the case. If there is a failure to meet the required regulations, the work will need to be rectified and re-inspected.

Building Control Fees

There is a fee for the inspections by a building control officer, but these vary between local authorities. If you have a private building control company that perhaps your building contractor uses regularly, this fee will normally be included in your quotation.

The use of private building control companies is useful for contractors who work in lots of different areas and deal with various local authorities.

Planning Permission for Extensions

Depending on your house extension plans and the area you live in, you may need to apply for planning permission.

Your architect or building contractor will be able to advise if the area that you want to develop in your property exceeds the permitted development allowance meaning that you will need to submit a planning application.

Single-storey side and rear extensions (including many bungalow extensions) can often be built under permitted development as long as they stay within the size limits. However, if you live in a conservation area, any side extension will need planning permission.

Two-storey or multi-storey extension plans will usually need to be submitted for planning permission, but this can vary according to the property and the area you live in. The cost to apply for planning permission for a house extension is currently £548 in England, £585 in Wales, £371 in Scotland, and £347 in Northern Ireland. These fees can change over time, so check the latest rate before applying.

Party Wall Issues

Under the Party Wall Act, you'll need to give your neighbour formal notice if you're building a wall on or along the boundary line, carrying out work to a shared wall, or excavating within 3 metres of next door to a depth below their foundations. This applies in England and Wales, and the notice must be served between 2 months and a year before work begins.

Any disagreement about the proposed works will need to be resolved through a party wall surveyor.

You'll usually cover the surveyors' fees as the person having the work done, although the surveyors will decide who pays.

Alternatives to Home Extensions

If you don't have the option of a home extension, then there are other things that you could consider if you need more living space in your house.

Summer House

A garden room or summer house is an ideal place to base yourself if you need to work from home or a nice chill-out zone away from the bustle of family life.

Most homes have some outside space, and there are many different designs of garden rooms or summer houses, so you are bound to find something suitable for your needs. And a big bonus is that a garden room usually won't need planning permission as long as it's single storey, isn't in front of the house and stays within the size and height limits.

Exceptions include a garden room at the side of the house in a conservation area, or any outbuilding in the garden of a listed building.

Shepherd Hut

A shepherd hut is an attractive space to either work from or use as a quiet space. They can sometimes be installed on private land without planning permission, but local rules vary and if you intend to rent them out as a B&B or similar, you would need to apply for the proper permission.

The option favoured by home buyers is typically the summer house or garden room as it allows extra living space such as a home office or chill-out area in the peaceful setting of the garden. A well-designed garden room can also increase the appeal of a property when it comes to selling.

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