House extension and conversion ideas

Moving to a bigger property can be an expensive, arduous process – and upsetting if you love your current home. If you need more living space, you could instead try adding to your existing property. 

There are various ways to extend your house. Here, we run through the extension types and offer advice on where to start with home improvement projects including garage conversions and extensions, front porches and expanding into the basement. 

Be inspired to make home improvements. Sign up for our Home newsletter – it's free monthly

Garage conversions and extensions

If you’re not using your garage to store a car, why not get the most out of it and create a new room? 

As the foundations are already there, it’s often a much cheaper way to create more space. 

Plus, garage conversions mean you won't lose any garden space like you would with a standard extension. 

Plus, once it's a functioning room it's less likely than a garage to get turned into a storage room that gets increasingly filled with stuff.

Before you begin

First, consult an estate agent about whether converting your garage could negatively impact your property's value. If you'll be living in your home for years to come, it may well be worth going ahead anyway, whatever they say, but if garages are highly sought-after in your area, think carefully before converting yours. 

Before you start work on the conversion, consider what you’ll do with everything currently kept in the garage. If you store a lot of garden gear and bikes in it, you may need to factor a shed into your plans. If it’s where you keep your large spare freezer, you’ll need to work out where it can be moved to – or whether you can live without it.

If you really have no room anywhere else for these things, perhaps a partial garage conversion (or a conversion that has lots of storage space set aside within it) will work better for you.

Attached vs detached garages

A garage conversion is one of the speediest and most affordable routes to adding extra space to your home. Plus, you won't need to move out while works are happening. If it’s integrated or attached, the garage should be fairly easy to work into the main house. 

If your garage is detached from the main property, you might need to apply for planning permission. In some circumstances it may be better to create a separate building that links back to the original structure, perhaps via a glazed corridor. This kind of approach can work especially well for heritage homes, where the planners may be keen on the idea of creating a distinct new zone subservient to the main house. A detached structure lends itself to segregated uses, such as an annex or quiet home office.

How much does a garage conversion cost?

Garage conversion costs are significantly lower than those associated with an extension because you will save money on laying new foundations and building new walls.

Your garage may also have power and perhaps even plumbing already, both of which will reduce your garage conversion cost even more. 

Head to our extensions costs page to unlock pricing data for extensions from the Building Cost Information Service (BCIS) database 

Do you need planning permission for a garage conversion?

With many garage conversions – particularly attached and integral spaces – most of the work is internal (with the exception of changing the frontage and adding a window or two). This is likely to be considered permitted development, so it won’t usually need formal planning consent. But check with your local authority before you begin.

However, if you live in a conservation area or listed building, you will almost certainly need planning permission and potentially also listed building consent. 

It is also worth checking for any planning conditions attached to the house or garage when constructed (for example, the garage has to remain as parking) before beginning works, as an application will need to be submitted to remove the conditions.

If your intention is to convert a garage into a separate house (regardless of who will occupy it), then planning permission may be required no matter what work is involved. Discuss such proposals with your local planning authority to ensure that any work you do is lawful and has the correct permissions.

What insurance do you need if converting a garage?

As with any type of extension, conversion insurance will cover the work and the existing structure. It should also cover materials, plant tools and equipment.

This type of insurance should also cover public liability and employer's liability – should any of the workers be injured on site, for example. Public liability and employers' liability are automatically included to ensure you are adequately protected, but do double-check to make sure it's definitely included. 

Ensure that the conversion insurance is ready to go from the moment work starts until the very end of the job.

Conversion insurance needs to be in place from the moment you plan to start work on the property and should continue to the point the project is completed and taken into full use.

Who designs and builds a garage conversion?

You can either design and oversee the project yourself and employ builders, or you can hire an architectural designer or a specialist garage design and build contractor, who will help put your ideas into fully formed plans and give you expert design input. The latter will of course be more pricey.

If the garage is attached or integral to your home, they will also help you consider the best position for access and put plans in place to redirect this if required.

With more complex projects, you may prefer to have full structural plans drafted. This gives you peace of mind that building control has inspected the drawings and confirmed that – if it’s constructed as per the approved plans – your conversion will conform to regulations.

In addition to structural safety, key areas your building control officer or approved inspector will look at are damp proofing, ventilation, insulation and energy efficiency, fire safety (including escape routes), electrics and plumbing.

Specialist garage conversion companies can save you time in putting together applications and will be experienced in getting the best from this type of project, but any good builder will be able to do the job. 

Head to Which? Trusted Traders to find a reliable local tradesman, or use our search tool:

Financial planning, save 50%

Members can get a financial plan and cashflow forecast with an Octopus Money expert for £149.50*

Book free intro session

You must be at least five years off retiring, other eligibility criteria apply. Offer ends 17 January 2025, T&Cs apply.

Replacing a garage door

The garage door will have to be replaced with a new wall and/or window. This may mean new foundations, but there are other options, including having lintels set just below ground level that bear on sound masonry or existing foundations at each end. 

If you live in a conservation area you might find that your local council will want you to retain the original door. Architects can often incorporate them stylishly into the new design.

For tips from a professional before kicking off a project, read our advice from a builder and architect 

Choosing a single or double-storey extension

Adding a single-storey extension will improve your home's layout and should increase its value. But could it be worth adding another storey while you're at it?

A single-storey extension is an ideal way to create extra living space in your home. It might allow you to expand an existing small kitchen into a kitchen dining and living space. It could also give you the extra space to add a utility room, a cloakroom or boot room.

A double-storey extension gives you all the above, plus extra bedroom and bathroom space upstairs. While it's more expensive, the cost won't be double that of a single-storey extension as a lot of the expensive structural work is already in place. 

So what are the differences between single, double and side-return extensions?

Double-storey or multi-storey extension

• Although more expensive than a single-storey extension, you tend to gain more space for your money per square metre. Find out the difference in our extension costs page.
• Depending on the size, you can either create larger versions of the rooms you already have or completely new ones.
• Gaining planning approval can be tricky as it tends to involve a lot of work and can drastically alter the look of a property. It can also seriously affect neighbouring properties, affecting their light and view.

Single-storey or full-width extension

• This type of extension tends to occupy the downstairs of a property and is often added to the rear.
• In some cases, it’s possible to extend the entire breadth of the house.
• Most people opt for this type of extension if they have garden space they can sacrifice to add a few extra metres to their house.
• It could also mean a second-floor extension above an existing ground floor.
• Quite likely to have to arrange a party wall agreement that protects the neighbouring properties. 
• Many people opt for large folding doors to connect the indoor and outdoor space and maximise light entering the property.
• Design can vary from flat roof to pitched roof with simple skylight windows, lantern windows to full glass roofs.

Compare Extension costs: how much should you expect to pay in 2024? and find out how much an average extension should cost per meter squared

Porch extensions

First impressions are important, so create a warm welcome for guests by adding a stylish and functional porch to the front of your home.

Whether you're after an extra bit of storage space for shoes, coats or stacks of firewood, a porch can be made bespoke to suit your needs. 

A porch does more than provide additional space to your home; it can add extra security benefits by being a barrier between your front door and the outside world.

Closed porches can also increase your home’s energy efficiency by preventing the heat escaping and helping you save a little on your energy bills.

Will a new porch need planning permission?

The planning rules for porches are applicable to any external door to the dwelling house.

Adding a porch to any external door of your house is considered to be permitted development, not requiring an application for planning permission, provided:

1. the ground floor area (measured externally) would not exceed three square metres.
2. no part would be more than three metres above ground level (height needs to be measured in the same way as for a house extension).
3. no part of the porch would be within two metres of any boundary of the dwelling house and the highway.

Remember that permitted development allowances apply to houses and not to flats and maisonettes and check if your property is listed or in a conservation area.

Porch designs

There are many design choices when it come to building a new porch, from windows, front door options, brickwork and different roof styles - including pitched, gable and flat, down to the smaller details such as lighting, door handles and flooring. Every element can be personalised to your taste and the rest of the property.

One of the most important aspects of installing a new porch is to integrate it into your existing home so it doesn’t look out of place, and just stuck on the front of your house. 

A good brick match is worth considering, as well as a similar roof material to help it look part of the original building. 

Read how to plan an extension for more in-depth advice, and find out how long it might take in our timeline to building an extension

Basement conversions and extensions

The premium on space, especially in cities, has seen interest in subterranean spaces soar as they become elevated from basic storage rooms to beautiful, fully functional living spaces.

A basement extension can be a clever way to expand your living space without taking away any garden space. Whether you fancy adding an extra bedroom, kitchen diner, or cosy snug, we take you through everything you need to think about, from planning permission to the pros and cons of creating a basement.

Do basement conversions need planning permission?

If you are converting an existing cellar and are not making any changes to the external appearance of the building, you are unlikely to need planning permission. But you will almost certainly need planning permission if you are making any structural changes or altering the external appearance of the property, if the building is listed or in a conservation area and if you are creating a separate unit of accommodation.

If your basement extension requires excavation to create more room or if  you are making changes to the external appearance of the property by adding a lightwell for example, you are likely to need planning permission.

Planning rules are continually being reviewed and vary considerably from one area to the next, so it is a good idea to contact your local planning authority at an early stage and well before any work begins.

Do basement extensions need building regulations approval?

Regardless of whether you need planning permission or not, you will almost certainly still require building regulations approval to ensure that  your conversion meets a minimum standard of health, safety and welfare conditions; this covers areas such as ventilation, fire safety, foundations and energy efficiency.

It may seem like there are an overwhelming number of professionals to consult when it comes to planning a basement extension, but speaking to a reputable local builder with experience of similar projects is the best place to start. Head to Which? Trusted Traders to find a reputable builder near you.

Your builder, architect or planning consultant should be able to provide you with a package of plans and structural drawings. They'll also work alongside local authority building control to achieve building regulations approval. 

The structural drawings will be provided by a structural engineer who will also produce technical drawings. 

Do I need a party wall agreement?

If your basement conversion requires structural changes to the building, such as excavation, you will likely require a party wall agreement. Some of the main criteria for requiring a party wall agreement includes:

• Excavating within three metres of your neighbour’s property and to a lower level than their foundations.
• Excavating within six metres and at an angle intersecting 45 degrees from the bottom of their foundations.
• Cutting holes into a shared wall to insert beams or flashing.

Party wall agreements aim to protect neighbouring properties during and after construction and in most cases will involve the serving of relevant notices and legal agreements to neighbours. 

Extending a property can often be a contentious issue with neighbours, so it's a good idea to inform them of any plans and contact a party wall surveyor at the early stages of your project.

For further information on party wall agreements, read our guide to building regulations and planning permission

How high does the basement's ceiling need to be?

Building regulations do not specify a minimum height for ceilings, but 2.4 metres is a practical height to aim for. 

You will need at least two metres over the stairs to keep within building rules. Don’t forget that you will need to include space for the height of your flooring within your calculations.

What's the best way to maximise light in a basement?

1. Light should be a major factor in deciding the basement’s layout. Position habitable rooms so that they get the best of the daylight and any outdoor access.
2. Ideally the landing area will have some natural light, most likely from the hallway above, to ensure safe passage.
3. Space near the centre of the floorplan or on elevations with no lightwells can be used for cloakrooms, bathrooms, storage spaces and utility rooms; all of which can function without natural light.
4. Consider a sunken courtyard garden, with glass doors accessing it or glass balustrades and open tread staircases to help light flow down from the floor above. Plus, glass partition walls and glazed or partially glazed doors allow light to filter through between spaces.
5. Where a basement extends beneath the garden, flat rooflights are a great way to bring in extra light.
6. Use neutral colours and finishes to enhance light and space.

Do basement conversions add value?

If you have outgrown your living space but you're keen to stay put, building an extension is a great way to make more of what you’ve already got. Adding an extra room, such as a converted basement, can increase your property value. 

We recommend you speak to a couple of local estate agents before you start; they will be able to indicate whether you will recoup your investment when selling. 

A good source of natural light and decent ceiling height will help to ensure that your conversion is a worthwhile investment that boosts your home’s value.

What are the pros and cons of building a basement?

Pros

• When you gain space from a basement, you don’t lose any external space. Plus, it will free up space in other parts of the house.
• Securing planning consent is generally easy, especially if there are already basement conversions in your street and if you have windows or light wells outside.
• In urban areas, a basement can add value.
• Underpinning can actually stabilise an old building.
• Waterproofing (or tanking) makes the whole house drier and healthier, and increased insulation makes it more energy efficient.
• It can be completely self-contained with its own access.

Cons

• The job is expensive and complex.
• It’s bound to be disruptive, noisy and messy especially if you are enlarging or creating more headroom and so there's the need to underpin.
• You need to have an annual (at least) inspection of the pump and drainage.
• There may be unforeseen problems, especially if there is a party wall.
• You may not be able to get enough light in and the room may end up gloomy or always dependent on artificial light.
• Safety may be a concern and you may end up having to lay out more money on another access route.

Here are some key questions to consider before going ahead:

Should I convert my basement?

If you're lucky enough to have a pre-existing cellar, it may make economic sense to exploit it by turning it into a habitable basement. If you don't, the process is trickier and might not even be possible.

The costs and complexity of the project will vary dramatically depending on whether you have an existing cellar or basement with enough headroom that can be easily converted; a basement conversion is likely to be much cheaper if it's an existing space with no structural changes needed. Or whether you will need to fully excavate beneath the house to make a basement possible.

The most cost-effective option is a simple utility basement with no windows, which would work well for a workshop, utility room, wine cellar, or just extra storage. With some investment in electrical and plumbing works, and finishes to the walls and floor, the basement space could be used as a games room, home cinema or gym.

If you're after a full lower ground floor with plenty of lightwells, your project will most likely require excavation and underpinning, which will be expensive. However, a functioning subterranean level could provide more functional rooms like a kitchen, office, guest bedroom and bathroom.

With a separate access via an external staircase, a basement could even be used as the home-based business or a self-contained annexe.

Before starting a home renovation, read our Where to start with a home extension: advice from a builder and an architect. To get an idea of how much you'll need to set aside, visit our guide to extension costs to unlock the latest pricing data from the Building Cost Information Service (BCIS) database.