If you’re in need of extra living space but don’t want to move, an extension is the way to go. And, extending your home over the garage often gives you space for that new bedroom, office or library – without eating into your garden.
Plus, if you add a loft conversion at the same time, you could add 45 or more square metres of living space to your home in one project. Of course, building an extension over a garage isn’t cheap.
In fact, the average cost of building an extension over a garage in the UK is about £30,000. You can also work that out to about £1,500-£3,000 per square metre of added space. Here, about half works out to materials and the rest to labour. However, the actual cost of an over-garage extension can range from £25,000 to over £90,000 depending on what you want.
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What Is An Extension Over A Garage?
An extension over a garage normally strips back the roof over your garage to install a flat floor and ceiling. You can then build a room over the space, up to the height of the top floor of the home.
This type of extension only works in homes that have a garage extending out from the house. That’s standard in the UK, where most garages are set to the front or to the side of the home.
However, building on top of the garage comes with some disadvantages. For example, you may have to reinforce the frame. In addition, the foundation may not be designed to support the weight of vehicles and an extra storey. Therefore, you’ll need a structural engineer on-board to ensure your modifications are safe.
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On the other hand, over-garage extensions allow you to add space to your home without reducing space in the garden. You also get to keep your car storage area, so the auto doesn’t have to go on the street. This means it adds more value than a back garden extension or a garage conversion. However, you can also expect it to cost more.
Over Garage Extension Costs Explained*
In most cases, you can expect to pay about £2,000 per square metre of extension space. For a garage of 14.5 square metres, that’s £29,000.
| Costs | Hours | Hourly Rate | Total | |
| £10-£50 | £7,660-£14,140 | |||
| Removing Roofing | 4-12 | £200-£600 | ||
| Bricklaying | 64-96 | £4,500-£5,760 | ||
| Roofing | 4-16 | £800-£2,400 | ||
| Electric Work | 1-4 | £50-£240 | ||
| Glazing | 2-4 | £200-£580 | ||
| Heating | 1-3 | £40-£180 | ||
| Drywall | 4+ | £40-£180+ | ||
| Insulation | 2-6 | £40-£240 | ||
| Removal of load bearing wall with doorway and windows | 2-8 | £400-£480 | ||
| Steelwork | 40-120 | £150-£720 | ||
| Structural engineer | 8-20 | £1,200-£3,000 | ||
| Materials & Fittings | £4,535-£21,910 | |||
| Brick | £2,000-£4,000 | |||
| Roofing | £960-£3,500 | |||
| Insulation | £180-£900 | |||
| Heating | £300+ | |||
| Drywall | £100-£300 | |||
| Light Fixtures | £50+ | |||
| Electrical | £145-£860 | |||
| Structural Steel | £800-£12,000 | |||
| Grand Total | £12,195-£36,050 | |||
*Please note these prices are based on quotes at the time of writing in May 2023. Actual costs are subject to change and may be different at the time of reading.
These costs are for a standard extension designed to be a bedroom or office. On the other hand, if you want an ensuite bathroom – it could cost as much as £10,000 extra for permissions and pipework.
Other Costs
| Costs | Total |
| Scaffolding | £1,800-£4,000 |
| Waste Disposal | £175+ per load |
| Temporary Roof Cover | £2,000+ |
| Building Control | £170-£690 |
| Planning Permissions | £60-£250 |
| Equipment Rental | £0-£4,500 |
Extension Above Garage Price Factors To Consider
The largest cost consideration when extending your home is whether the foundation can support the extension. However, there are plenty of other considerations like the cost of labour.
Structural Engineering
Fitting an extension over a garage can require a significant amount of structural engineering.
Here, you’ll typically have to start with an inspection to determine if the building is structurally sound to support an extension. This means evaluating the foundation, the frame and the weight distribution of the building across the foundation.
You’ll typically pay at least £400 for this service.
However, rates can be significantly higher. Structural engineers either charge an hourly fee (£75- £160 per hour) or a percentage of the project. In either case, the total fee may be anywhere from under £1,000 to over £4,000 depending on the volume of the work.
Your structural engineer will assess whether it’s safe to extend the home. Then, they’ll draw up plans to allow you to safely do so by using structural steel to support the new floor.
You can also use this plan for planning permissions if you’re required to apply for them because of a bathroom or the size of the extension.
Labour Required
Your extension project can vary significantly in scope depending on your home.
For example, you could want to remove the existing flat roof of your garage, install structural steel to reinforce it and then add a prefabricated building on top. This is likely to be completed in a month or less.
Or, you could have a standard situation, in which the foundation is fine. However, you have to add structural supports to the building, replace the roof and then build on top of it.
In addition, local regulation requires that you match new materials to the old building, so you’ll need scaffolding and brickwork. That will mean a build project of 2-3 months.
On the other hand, your garage and foundation might not support an extension. But you want one anyway.
So, you tear down the garage and remove the foundation under it. Then you pour a new slab and build a new two-storey garage and bedroom in whatever size you want. That could add 2 or more months to the project.
Local Cost of Labour
The simplest extensions use prefabricated materials and install within a few weeks. The most extensive can take up to 6 months. On average, your over-garage extension is a 2-3 month project. This means you’ll pay 2 or more builders for full-time labour for a season. That can be extremely expensive.
In most cases, you’ll get either a day rate per labourer or a project rate. Either way, it should work out to about £150 per day per person on the job.
Here, assistants, apprentices and low-skill labourers may earn slightly less and project managers and master-level technicians will earn more, but it should average out to about £150. However, if you’re in London, Wales or parts of East England where living costs are higher, you can expect that day rate to go up to £200 or even £250.
What does that mean for your project? Labour is usually between £7,500 and £14,500 for most projects. However, it could be higher.
Materials
Materials can be an extremely costly element in building an extension. Here, structural steel and brick are likely to be the most expensive.
On the other hand, if you don’t have to use brick, you might opt for a cheaper steel frame with metal or uPVC siding.
On average, you’ll pay the following costs for materials:
- Structural steel – £66 per metre
- Brick – £100-£160 per m2 of brick and mortar (not including labour)
- Insulation – £5-£25 per m2
- Roofing materials – £20-£175 per m2
Essentially, if you need a new steel frame to support your new floor, reinforcements for the floor and a steel structure to support the brickwork, you’re looking at a lot of structural steel. That can be extremely pricey.
However, materials are unlikely to cost more than about £20,000 unless you specifically look for luxury materials.
Amenities
A basic bedroom or office will cost in the lower range of listed installation costs. However, if you add bathrooms, underfloor heating, etc., you can expect costs to rise.
A bathroom can cost £10,000 or more over the costs listed, simply because you may have to completely reroute your soil pipes and waterpipes, which may mean lifting the floor.
In addition, bathroom units can cost anywhere from about £100 to over £5,000 each depending on brand and quality.
Safety and Work Tools
Building an extension on your garage means that you’ll have to remove the existing roof and then have people work at height. This means you’ll need safety and work tools that you wouldn’t need for a ground-level installation. For example, you’ll need scaffolding.
In most cases, that will mean renting scaffolding, although your construction company may supply it as part of the project. Here, you can expect rates to run between £1,800 and about £4,000 – although it may be more for a 6-month project or a 3-storey build.
In addition, you’ll need temporary roof coverings, which prevent damage to the interior of the garage and the walls between removing the old roof and installing the new ceiling. That can cost several thousand pounds.
Benefits Of Extending Your Home
Extending your home can add a lot of benefits, most notably, adding living space that you might need.
Adding Living Space
Whether that’s for expanding space for social life, hobbies, working out or sleeping space – an extension can make it happen. For example, if you’re expanding the family, you might need a new bedroom for kids. That’s also true if kids are getting older and need a bedroom for themselves. Or, if you’re moving to a work-from-home situation and need a home office.
More living space means more freedom to do what you want in the home – which can take many shapes and forms.
Increasing Home Value
More living space means more value if you’re looking to sell your home. In fact, the average cost of property sold in the UK was £3,000 per square metre across the UK.
Of course, that ranges from a low £1,000 per m2 in Grimsby and Rhondda and goes to over £6,000 in Greater London. But, on average, you’ll make a profit on your home extension, unless you spend more than £3,000 per square metre.
In addition, larger homes may be more in-demand. However, a larger home may take more time to sell, simply because you’re not aiming at starters.
So, there are trade-offs, but you’ll almost always be able to fetch a higher asking price, whether the add-on is an ensuite bathroom or a new bedroom.
Preventing a Move
If you moved into a starter home and fell in love, moving can be difficult. In addition, the cost of new housing can be extremely high.
Costs of property in London, the Southeast and the East of England all average over £3,000. And, the cost of buying new housing is, on average, as much as twice that of building an extension. So, fitting an extension can be cost-saving over moving house – even if you spend £3,000 per square metre.
Building Regulation
You’ll always have to notify building control of a notification. However, providing your contractors are part of the Competent Person’s Register, they can self-inspect and report for you.
Depending on your location, notifying the council will cost £170 to £690.
However, if your tradesperson or the people they contract aren’t part of the Competent Person’s Scheme, you’ll have to pay for council safety inspections at every step. These typically start out at £100 each.
Planning Permission
Extensions are normally considered to be part of approved planning for your home. Therefore you won’t always need planning permission. However, you may if:
- Plans include installing a new bathroom
- You’re using a different street-facing material than the original house
- The foundation has to be replaced
- You’re increasing the height by more than one storey or a single storey extension has already been added
- A veranda or balcony is included in the plans
- You’re expanding by more than 40-50 cubic metres from the original space
- The original eaves are not being replaced
- Your extension overhangs the outer facing of the house
In each of these cases, you’ll have to submit plans for planning permission. This is also true if you live in a listed home.
Here, the initial application typically costs £50 but you can expect total costs to average around £260 with no complications, such as rejected plans. In addition, planning permission may take 6-8 weeks to process your application.
If you need planning permission, you’ll have to wait till you find a builder and till you have structural planning drawn up. This means the full process can be a 2 month or further delay on your project. That is often more of a setback than the actual cost of planning permissions.
Over Garage Extension Building Timelines
The timeline for building your over garage extension will heavily depend on how much work needs to be done. However, a standard build project, with no foundation replacement, looks like this:
- Find a builder
- Inspecting the Home and Foundation – 1-2 days + 1+ weeks for processing data
- Drawing up plans and safety schematics – 1-2 weeks
- Submitting plans to city council (if required) – 6-8 weeks
- Installing scaffolding – 1-2 days
- Removing original roof – 2-3 days
- Installing temporary roof cover – 1 day
- Constructing steel frame and floor – 2-3 weeks
- Brickwork – 1-2 weeks
- New roof – 2-5 days
- Interior electrical work – 1 day
- New floors – 2-3 days
- Cutting doors and removing interior walls – 1-4 days
- Installing glazing – 1+ days
- Interior finishing and drywall – 1-4 days
- Plaster, paint and finishing – 2+ days
Complications will always mean the project takes longer. In addition, this timeline doesn’t take into account that you might have to wait periods for electricians or plumbers to be available or for delivery of steel, brick or other materials.
In addition:
- Tearing down existing garage – 2-3 weeks
- Replacing the foundation – 2-6 weeks
- Breaking up foundation to lay a soil pipe for an ensuite bathroom – 2+ weeks
You can also face unusual costs, like having difficulty finding materials to match the original facing of the home. For example, if you have an unusual rock or stone facing, finding matching material can require significant time.
Extension Builder Hiring Checklist
Hiring a good builder is important, as they’ll be literally taking apart your home to add to it.
- Are you registered with the Competent Person Scheme?
- Do you subcontract electricians and plumbers or do I have to handle that myself?
- What about relevant qualifications such as CIAT, FMB, RIBA or RTPI?
- Do you offer workmanship guarantees?
- Is liability insurance included?
- What about worker’s liability?
- Does the quote detail all work and materials?
- Who’s responsible for waste disposal?
- Do you have good reviews online? What about references?
- Who owns leftover materials?
And, of course, you should always talk with the builder in question to get an idea if you’re going to be comfortable having them in your home for several months.
Next Steps
The first step to hiring a builder is to look at and compare local quotes. Building an extension over your garage can cost anywhere from £1,500- £3,000 per square metre.
In most cases, those cost differences are about materials, build-complexity and location. However, you might find that some builders charge more because they are more in demand and have less available time, others charge less because they have all the tools for the job, etc.
Therefore, you’re always best-off looking around, quoting your project well and choosing after looking at what all your options charge.
If you’re ready to get started, use the form at the top of the page to request quotes for an over garage extension from builders in your postcode.