Full vs. partial conversion
Converting one bay and keeping the other for storage can save £5,000–£8,000+ compared with a full conversion.
Enough room for two separate spaces, one large open-plan room, or a fully self-contained annex with its own kitchen and bathroom. Read our full cost guide and use the calculator to see what your project would cost.
Compare up to 4 vetted local garage conversion specialists. Free, no obligation.
Typical all-in prices including labour, materials, insulation, plastering and VAT. Prices vary with garage condition, specification and region.
| Item | Typical Cost | % of Total |
|---|---|---|
| Garage door removal & wall/window | £2,800 | 19% |
| Insulation | £3,200 | 22% |
| Flooring | £2,200 | 15% |
| Electrics | £2,600 | 18% |
| Plastering | £1,600 | 11% |
| Decoration | £1,300 | 9% |
| Building Regs / fees | £900 | 6% |
| Subtotal | £14,600 | 100% |
These figures cover the main trade and material costs for an integral double garage of around 30m² with a basic-to-mid specification. They exclude architectural drawings of £600–£2,500 and structural engineer calculations of £600–£1,400 where needed. Contractor markup and contingency are also not included. This is why the full project cost on this page is £18,000–£30,000. A detached garage, en suite bathroom, kitchenette or premium finish can push the total to £25,000–£38,000+.
Converting one bay and keeping the other for storage can save £5,000–£8,000+ compared with a full conversion.
One open-plan room costs less than adding partitions, extra doors and duplicate electrics.
Detached doubles cost more due to independent services and full insulation compared with integral or attached garages.
Adding plumbing for an ensuite or kitchenette can add £10,000–£20,000+ to the total conversion cost.
Raising and damp-proofing a double garage costs more because there is twice the floor area to treat.
Larger rooms may need extra fire escape measures or compartmentation, especially when creating multiple rooms.
A double garage offers you options and flexibility that a single garage simply cannot offer. You can either turn all the space to one big room or use one bay for parking/storage and the other bay to create more living space. That's why you should decide how you would like to utilise the garage before you start getting quotes.
Double garage conversions in the UK can cost between £15,000 and £38,000 depending on the size of the garage you will transform and what you change it into. The cost of converting one bay is slightly higher than a single garage conversion, whereas a full conversion to make a large living space or a self-contained annexe is the most expensive on this price range.
Double garage conversion costs between £15,000 to £38,000 and the average for most homeowners is between £18,000 to £30,000 for a full conversion. The average measurment for double garages in the UK are between 28 to 36 m² and conversion costs are around £800 to £1,500 per m². The price per square metre is often cheaper than a single garage since many fixed costs are distributed over a larger floor area.
If you convert one bay and leave the other as parking or storage you are looking at £8,000 to £18,000 which brings the price considerably closer to a standard single garage conversion.
Use the calculator on our website to get an idea of the rough costs involved for your desired garage conversion.
This is the most important decision you will have to make with your double garage.
Full Conversion
Full conversion means that you convert the whole garage into living area. This is ideal for uses like a large family room, open plan living area, home office or a bedroom with en suite. Overall it costs more but gives you more practical space for your money as many of the fixed costs of the project are still the same.
Split Conversion
A split conversion creates one bay for car parking or storage purposes and converts the other one into usable space. A new stud wall splits the garage into two spaces so that you can use one space as garage storage or want to keep off-road parking. The cost of the converted half will be almost same to any standard single garage conversion.
Neither option is completely right or wrong. If parking is limited where you live the keeping one bay may be a better choice but if your priority is to create more living space then a full conversion makes more sense for you.
Following are the three things that have the biggest impact on the cost of a double garage conversion:
How much you convert. Converting the whole garage is more expensive than converting just one bay but the price per square metre is lower as many fixed costs still stay the same.
Garage type. Integral and attached garages are less costly to convert as all required services are already closer. If you have a detached double garage then you will have to pay extra and the extra costs will range between £5,000 to £10,000 or more.
How you'll use the space. A home office, playroom or bedroom costs much less than a conversion that includes a kitchen or a bathroom. Things like plumbing, drainage and ventilation all add to your budget and this is why annexes and self-contained living spaces are very costly to convert.
Condition. A garage that is dry and in an overall good condition will cost less to convert than one with damp, roof problems or damaged floor. If these repairs are needed before the work can begin, the overall cost for your conversion project will definitely will increase.
Labour
The labour charges account for around 60 to 70% of the total project cost. A double garage conversion takes longer than a single garage conversion and involves several trades, including builders, electricians, plumbers, plasterers and decorators.
Structural work
A larger garage doesn't automatically mean that everything will cost double for you. There cost of certain things like structural calculations and professional fees change very little whether you are converting one bay or two.
| Item | Cost |
|---|---|
| Garage door removal and wall infill (both bays) | £2,200 – £3,200 |
| New stud wall (split conversions) | £750 – £1,200 |
| New windows and/or doors | £1,800 – £3,000 |
| Floor slab upgrade | £1,800 – £2,800 |
| Structural engineer (if required) | £600 – £1,400 |
Insulation and damp-proofing
In order to bring your garage structure up to current building regulations, will have to pay an extra £2,500 to £6,000. The cost includes things like proper insulation and damp-proofing.
Electrics and plumbing
The installation of lighting and sockets in your newly converted garage will cost you between £1,800 to £3,000. If you are adding a kitchen or bathroom to the garage, the plumbing cost for either one of them can range between £3,500 to £7,000 and if you choose to add both, you are looking at anywhere between £9,000 to £16,000.
Building regulations and professional fees
| Item | Cost |
|---|---|
| Building control application | £400 – £1,200 |
| Architectural drawings (if needed) | £600 – £2,500 |
| Lawful Development Certificate (optional) | £124 – £310 |
Quotes and VAT
Most builders will include the VAT in their quotes but make sure to check this item before comparing prices. It is a good idea to hire a contractor who has experience converting double garages =, especially if you are adding a kitchen, bathroom or annexe.
| Use | Cost |
|---|---|
| Split conversion (one bay converted) | £8,000 – £16,000 |
| Full family room or open-plan living space | £15,000 – £22,000 |
| Bedroom with en suite | £20,000 – £30,000 |
| Self-contained annexe | £28,000 – £38,000+ |
A split conversion is ideal if you want to keep some parking or storage while creating an extra room whereas a full conversion costs more but gives you a much larger living space. Adding an en suite increases the cost because you have to take care of things like plumbing, drainage and ventilation, while a self-contained annexe with its own kitchen and bathroom will cost you the most.
| Region | Typical variation |
|---|---|
| London & South East | 15–25% above national average |
| Midlands & East of England | Close to national average |
| North England | 10–15% below national average |
| Scotland & Wales | 5–20% below national average |
A double garage conversion costing £24,000 in one part of the UK could cost £27,600 to £30,000 in London or the South East whereas in many parts of the North, Scotland and Wales, the same project may cost less.
Because a double garage conversion is a larger investment, it's worth comparing quotes from several experienced contractors before making a decision.
Planning permission
Most double garage conversions don't need planning permission because the work is carried out inside the existing building. In many cases, the conversion falls under Permitted Development.
You may need planning permission if:
If you're planning a kitchen and bathroom in your converted garage then it is recommended that you consult with your local council before work gets started. Even if planning permission is not required by low, you should still get a Lawful Development Certificate (£124 to £310) as this will be your proof that the conversion was done lawfully.
Building regulations
All double garage conversions need approval under building regulations in the UK. The work shall comply with standards relating to structure, insulation, ventilation, fire safety and electrical installation.
If you are creating a self-contained annexe then there may be extra requirements for fire separation and escape routes. The usual building control fee is between £400 and £1,200 and inspections will be made throughout the project.
A few costs can catch you out if you don't include them in your budget from the start.
Pre-conversion survey (£400 to £800). A survey can uncover damp, roof or floor problems before work begins, helping you avoid expensive surprises later.
Contingency. Keep aside 10 to 15% of your budget for unexpected work. On a £24,000 conversion, that's £2,400 to £3,600.
Council tax. If you're creating a self-contained annexe, it could be given its own council tax band. It's worth checking with your local council before work starts.
Party wall agreement. If your garage shares a wall with a neighbouring property, some structural work may require a party wall agreement.
Garage door layout. Some double garages have one large door instead of two separate doors. This can affect the cost of removing the opening and building the new front wall, so make sure your quotes reflect your garage's layout.
Utility upgrades. Adding a kitchen or bathroom may mean upgrading your home's electrical supply or water services as well as running new pipes and cables to the garage.
The best way to budget for a double garage conversion is to plan the project before you start requesting quotes from contractors.
Decide whether you're converting one bay or both. This has the biggest impact on the final cost.
Measure your garage. Record the internal floor area in square metres and note whether there's already a dividing wall between the two bays.
Decide how you'll use the space. A home office or family room costs much less than a conversion with a kitchen or bathroom.
Get at least three itemised quotes. Choose builders with experience converting double garages and ask for a breakdown covering structural work, insulation, electrics, plumbing, building regulations and finishes.
Check planning and council tax requirements. If you're creating a self-contained annexe, make sure you understand any planning or council tax implications before work begins.
You can use the calculator on our platform to get an instant estimate based on the size of your garage and the type of finishing you want and then compare quotes from vetted local contractors.
Double garage conversion vs house extension
One of the most economical methods to add a large amount of living space for living to your house is through a double garage conversion. It costs a lot less than building an extension of the same size because the walls, roof and foundations already exist.
Full or split conversion?
You can save a bit of storage or parking space with a split conversion and it is less expensive. A complete conversion will cost more but you're going to end up with a much larger room. The additional space also makes it a much more practical option if you are looking to construct a self-contained annexe.
Does it add any value?
A well-finished conversion of a double garage can add value to your home, especially if it results in an additional bedroom suite or a self-contained annexe. Before you convert the whole garage, think about what losing two outdoor parking spaces might mean to future buyers.
How to keep costs down
Everything UK homeowners ask us about double garage conversion costs, planning and building work.
You can convert one bay of a double garage and still keep the remaining space for parking or storage. This will cost you a similar amount to converting a single garage, at £8,000 to £16,000.
Yes, normally. A double garage conversion usually costs £800 to £1,500 per square metre, whereas a single garage costs £900 to £1,800. This is because costs such as building control fees and structural calculations are spread across more floor space.
The most expensive use of a double garage is a self-contained annexe with its own kitchen and bathroom but also the most practical, given the space available, at £28,000 to £38,000 or more.
Adding a dividing stud wall to split the space into two rooms usually adds £750-£1,200 to the project, plus the expense of separate heating and lighting circuits for each room if required.
Average cost for a double garage with en suite bedroom is between £20,000 and £30,000 with one bay for the bedroom and the other for the bathroom and any additional storage.
A self-contained annexe with its own kitchen and bathroom can have its own council tax rating. It’s worth checking with your local council prior to finalising your design, especially if you plan to let it out.
In addition to the headline quote, budgeting for a larger pre-conversion survey (£400 to £800 given the larger floor area), a 10 to 15% reserve, and a party wall agreement, if your garage shares a wall with a neighbouring property.
A full conversion costs more in total but more effectively utilises the fixed costs that come with any conversion project, so you get more usable space per pound spent. A split conversion costs less and allows for some parking or storage, which is more important if off-street parking is scarce in your area.