Double Garage Conversion Cost Guide for UK Homeowners

Quick Cost Breakdown

• The average cost of a double garage conversion in the UK is £15,000-£30,000.
• A high-end conversion with plumbing, underfloor heating, or bi-fold doors can cost £30,000-£45,000+.
• The main cost factors are garage size, structural condition and the type of room you're creating.

Your Double Garage Conversion Cost Guide

In this cost guide, we’ll cover:

1. Is Converting My Double Garage Worth the Cost?
2. Labour Costs for a Double Garage Conversion
3. Double Garage Conversion Cost by Room Type
4. Attached vs Detached Double Garage Conversion Cost
5. When Do I Need Planning Permission for a Garage Conversion?
6. Cost-Saving Tips for a Double Garage Conversion
7. Find Conversion Specialists Near You on MyBuilder
8. FAQ: Common Questions About Double Garage Conversions

Is Converting My Double Garage Worth the Cost?

If your double garage has become an oversized storage unit for bikes, boxes, and things you forgot you owned, it might be time to make better use of it.

A double garage conversion is one of the most cost-effective ways to add living space in the UK. The structure is already there, foundations, walls, and roof, so the cost per square metre is far lower than building from scratch.

The average double garage conversion cost of £15,000-£30,000 compares very favourably to house extension costs, which can easily run to £50,000-£90,000 for a comparable footprint.

Your double garage space is typically big enough for:

• A two-bedroom layout with a shared hallway
• An open-plan kitchen-diner or family living room
• A home office and gym side by side
• A fully self-contained annexe with bathroom and kitchenette

According to research from the Federation of Master Builders, a well-finished garage conversion adds around 10–20% to a property's value, often more than the cost of the conversion itself. That makes it not just a practical improvement but a sound financial one.

The best way to understand what your conversion will cost is to get a garage conversion specialist to assess the space in person. You can find conversion specialists on MyBuilder and request quotes from tradespeople in your area.

Ask a conversion specialist

Labour Costs for a Double Garage Conversion

Labour typically makes up 40–50% of the total double garage conversion cost.

With double the floor area of a single garage, each trade spends longer on site. Because of this, you're more likely to need additional trades, particularly if the conversion involves plumbing, structural steelwork, or a new external wall with a wide glazed opening.

Here's what you can expect to pay by trade:

Trade	Day Rate
Builder / bricklayer	£150-£250
Electrician	£200-£300
Plasterer	£150-£200
Plumber (if needed)	£200-£300
Carpenter / joiner	£150-£250
Decorator	£120-£200

For a mid-range double garage conversion with no plumbing, total labour costs usually sit around £5,000-£9,000. Add a bathroom or kitchen and that rises to £9,000-£14,000. In London and the South East, day rates typically run 15-25% higher than the national average.

For a more detailed breakdown of individual trade costs, see our electrician hourly rate guide or cost of plastering guide.

Should you hire a main contractor?

For a double garage conversion, a main contractor is worth serious consideration.

With more trades involved, longer timelines, and greater complexity than a single garage project, having one person coordinate the schedule, manage deliveries, and handle building control inspections at key stages can save significant time and stress.

Expect a 10-20% markup on top of individual trade costs for this service - but on a project of this scale, the coordination alone often justifies it.

Also, you should check carefully whether items such as plumbing, electrics, heating, and finishing work are all included. Some contractors quote for the structural shell only. Always ask for a detailed breakdown so you can compare like for like.

Find a contractor near me

Double Garage Conversion Cost by Room Type

With 300-36m², a double garage opens up room types that simply aren't possible with a single garage. You can create one large space, two separate rooms, or a hybrid combination.

The room type you choose will have the single biggest impact on the overall cost of your double garage conversion, largely determined by whether it's a "dry" conversion (no plumbing) or a "wet" one (bathroom, kitchen, or kitchenette).

Open-Plan Home Office

The double garage's width makes it ideal for a spacious home office with room for a desk, meeting area, and storage. Good insulation, plenty of sockets, dedicated data points, and a large window or glazed doors for natural light are the essentials. There's no plumbing involved, which keeps the cost firmly at the lower end. Budget £12,000–£18,000.

Two Separate Bedrooms

Splitting the space with a partition wall creates two decent-sized rooms, each around 14-16m². You'll need a hallway or landing area between them, plus individual heating, lighting, and ventilation for each room.

Building Regulations require a minimum ceiling height of 2.4 metres for a habitable bedroom, so check this before committing to the layout. Soundproofing between rooms adds cost but is well worth it, particularly if the conversion is intended for long-term residential use. Budget £18,000-£25,000.

Master Bedroom With En-Suite

One of the most popular double garage conversion layouts. The extra width gives you a generous bedroom plus a proper en-suite shower room without either space feeling cramped. Plumbing runs, tiling, waterproofing, and the wet room or shower enclosure account for most of the cost difference over a dry conversion. You'll also need an extractor fan and possibly a heated towel rail circuit. Budget £20,000-£28,000.

Home Gym and Office

Split the space into a gym area with rubber flooring, reinforced wall mounts, and good ventilation on one side, and a finished office space on the other.

A simple partition wall or even a glazed screen keeps the two zones distinct without fully separating them.

It's worth specifying reinforced flooring early, standard screed isn't designed for the repeated impact of heavy weights or treadmills. Budget £10,000–£16,000, making it one of the more affordable double garage conversions.

Self-Contained Annexe

The premium option, and the one with the most significant planning implications. A double garage has enough space for a genuine one-bed flat: living area, bathroom, kitchenette, and separate entrance.

This involves full plumbing and drainage runs, extraction, upgraded electrics, and potentially a separate utility meter.

At £28,000-£45,000, it's the most expensive conversion type, but a detached double garage with its own entrance can generate rental income or provide genuinely independent living space for a family member.

Not sure which room type suits your space? Every garage is different, ceiling height, natural light, proximity to drains, and access all play a part in what works best. A local conversion specialist can visit your property, assess the space, and recommend the most practical option for your budget.

Attached vs Detached Double Garage Conversion Cost

Whether your double garage is attached to the house or standing separately in the garden has a significant impact on the cost of a double garage conversion.

Attached Double Garage

An attached garage shares at least one wall with the main house and usually has existing utility connections close by. Extending the central heating, running electrics, and tying into the drainage system is relatively straightforward.

Typical costs range from £15,000-£28,000, making it the more cost-effective route when services and structure are already close at hand.

Detached Double Garage

A detached garage requires its own utility connections run from the main house - electrics, water, and drainage all need to be extended across the gap, which adds both cost and complexity.

Typical costs range from £22,000-£40,000, and higher if you're planning a self-contained annexe with independent living provision.

A detached conversion costs more upfront, but it offers something an attached garage can't: complete separation from the main house, with its own entrance and no shared walls.

When Do I Need Planning Permission for a Garage Conversion?

Most double garage conversions in the UK fall under permitted development rights, meaning no formal planning application is required.

However, there are important exceptions, and regardless of whether planning permission is needed, building regulations approval is always required.

When planning permission is needed:

• The property is in a conservation area or is a listed building
• You are creating a self-contained annexe (change of use)
• The conversion involves significant external alterations that change the building's appearance
• Your permitted development rights have been removed by a local planning condition

A planning application in England currently costs £206 for a householder application, plus any architect or planning consultant fees if you need drawings prepared. Allow 6-10 weeks for a decision if full planning permission is required.

Lawful Development Certificate: Even when permitted development applies, it's worth obtaining a Lawful Development Certificate as proof that the work was legal.

This costs £103 in England and is particularly valuable when selling the property, buyers' solicitors routinely ask for evidence of planning compliance on conversion work.

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Cost-Saving Tips for a Double Garage Conversion

There's no need to compromise quality to keep the cost of your double garage conversion in check. A few well-considered decisions early in the project can save thousands without affecting the finished result.

• Keep the existing floor slab where possible. If a structural engineer confirms it's sound and at the right level, insulating on top with rigid PIR foam boards rather than replacing the slab entirely can save £1,000-£3,000.

• Avoid unnecessary plumbing. If you don't need a bathroom or kitchen, keeping the conversion dry saves £4,000-£8,000 in plumbing, drainage, tiling, and waterproofing costs. A home office, gym, or bedroom without an en-suite are all strong options that keep the budget firmly in the lower range.

• Go open-plan where possible. Every internal partition wall adds cost, framing, insulation, plastering, and an extra door. If the layout works as one open space, it's almost always cheaper to leave it that way.

• Choose standard materials. Engineered wood flooring, off-the-shelf doors, and a brick infill with standard windows cost a fraction of bi-fold doors and bespoke joinery. Reserve the premium finishes for the elements that matter most to you and keep the rest straightforward.

• Get multiple quotes. Prices vary significantly, even between tradespeople in the same area. Posting your project on MyBuilder lets you compare quotes side by side, read reviews from previous customers, and find the right balance of price and quality without spending days ringing around.

Find Double Conversion Specialists Near You on MyBuilder

Post your project for free on MyBuilder to receive quotes from local tradespeople who are available and interested in your job. You can read reviews from previous customers, browse photos of completed garage conversions, and compare options side by side, so you can choose the right person for your project and your budget.

All tradespeople on MyBuilder undergo checks at registration, such as ID documents, company details, certifications for regulated jobs and skill assessments, allowing you to hire with confidence.

Find a conversion specialist

FAQ: Common Questions About Double Garage Conversions

How Long Does a Double Garage Conversion Take?

A straightforward double garage conversion, an open-plan room with no plumbing, typically takes 4-6 weeks on site. More complex projects with partition walls, a bathroom, or a kitchenette can take 6-10 weeks. A self-contained annexe with full plumbing, drainage, and a separate entrance can run to 10-4 weeks or more. Poor sequencing of trades is one of the most common causes of delays, which is another reason a main contractor with experience coordinating multiple trades can be worth the premium on a project of this size.

Does a Double Garage Conversion Add Value to Your Home?

Yes, often more than a single garage conversion because of the additional square footage. A well-finished double garage conversion can add 10-20% to your property's value, particularly if it creates extra bedrooms or a self-contained living space.

Estate agents consistently rank additional bedrooms and self-contained living space among the most in-demand features for UK buyers. You can browse photos of completed garage conversion projects on MyBuilder to get a sense of the standard of work and the types of finishes that perform well.

Can You Split a Double Garage Into Two Separate Rooms?

Absolutely. It's one of the most popular layouts for a double garage. A timber-framed partition wall with soundproofing insulation divides the space neatly, and each room gets its own door, window, heating, and lighting circuit. Building Regulations require that each habitable room has adequate ventilation and a minimum ceiling height of 2.4 metres. The partition itself typically adds £1,500-£3,000 to the project, including framing, insulation, plastering, and a door.

Do You Need a Structural Engineer for a Double Garage Conversion?

Yes. And it's even more important for a double garage than a single one. Removing two garage doors creates a significantly wider opening, and the new front wall needs properly calculated steelwork to support the load above.

A structural engineer's report costs £300-£600 and is required by building control before work begins. If the existing slab has shallow foundations or shows signs of movement, the engineer may also recommend remedial work, which is far better to know about before work starts than to discover mid-project.

Can You Convert a Double Garage Into a Separate Dwelling?

You can, but it requires planning permission as it constitutes a change of use from a garage to a residential dwelling. You'll also need to meet all building regulations for a habitable dwelling, including separate utility connections, fire safety provisions, and adequate insulation to current standards.

In some cases, the new dwelling may be assigned its own council tax band. It's the most complex and expensive type of conversion, but a detached double garage with its own entrance is one of the best-suited structures for it in terms of space and layout.