A garage conversion is one of the fastest and most cost-effective ways to add usable living space to a London home, because the structure, the roof and the foundations already exist. Across London in 2026, a straightforward integral or attached garage conversion typically costs £18,000 to £42,000, with an en-suite bedroom or detached annex running higher.

At a glance

  • Basic conversion: £18,000 to £28,000, typically a home office, playroom or utility room
  • Mid-range conversion: £28,000 to £42,000, a bedroom or larger living space with full insulation and finishing
  • Bedroom with ensuite: £32,000 to £50,000, including new plumbing and a compact bathroom
  • Typical timeline: 2 to 4 weeks for a basic conversion, up to 12 weeks for a more involved scheme
  • Planning: most integral and attached garage conversions fall under Permitted Development

Integral, attached and detached garages

An integral garage sits within the main footprint of the house, sharing walls, roof and often a floor slab with the property. These are the cheapest and quickest garages to convert, because heating, electrics and internal access are usually already close by. An attached garage, built onto the side of the house but with its own separate roof, needs slightly more work to bring the roof up to insulation standard, since there is no habitable room above it to consider structurally.

A detached garage sits apart from the house entirely. Converting one into a home office, studio or annex is straightforward in principle, but it requires new electrical, and often plumbing, connections run out from the main house, and any change of use to independent residential accommodation is more likely to need planning permission.

What a garage conversion costs in London in 2026

A basic conversion into a home office or playroom, with insulation, a new floor, electrics and plastering, typically costs £18,000 to £28,000 including VAT. Moving up to a proper bedroom with heating and a higher specification finish takes that to £28,000 to £42,000. Adding an ensuite bathroom, with new drainage connections and a compact suite, pushes the total to £32,000 to £50,000. A detached garage converted into a self-contained annex, with its own kitchenette and bathroom, generally sits between £22,000 and £65,000 depending on services and specification.

Key cost drivers include the condition of the existing structure, whether the roof needs upgrading to modern insulation standards, and whether you replace the garage door with a wall, window or set of French doors, which changes the external appearance and the amount of glazing work involved.

Planning permission and Building Regulations

Most integral and attached garage conversions in London do not need planning permission, because the external footprint of the house is unchanged. This applies as long as your permitted development rights have not been removed by an Article 4 direction, common on some newer estates, and provided the front elevation and driveway are not significantly altered.

Building Regulations approval is mandatory for every garage conversion regardless of planning status, covering insulation, damp-proofing, ventilation, fire safety and structural adequacy of the existing garage floor and walls. We recommend applying for a Lawful Development Certificate even where planning permission is not strictly required, since it provides written council confirmation that becomes valuable at resale.

Our garage conversion process

We survey the existing structure to check the floor slab, roof condition and damp-proof course before quoting, since these determine how much preparatory work is needed before finishing can begin. From there we handle infill of the garage door opening, floor build-up and damp-proofing, insulation to current Building Regulations standards, first-fix electrics and any plumbing, then plastering, flooring and decoration.

Because a garage conversion is largely internal work, disruption to the rest of the house is minimal, and most projects are completed within a matter of weeks rather than months.

Why choose Alpha London Builders for your garage conversion

We treat garage conversions with the same fixed-price, fully certified approach as our larger projects. Every conversion includes Building Regulations sign-off and, where applicable, a Lawful Development Certificate application, so you have the paperwork you need whether you are creating a home office today or planning to sell in future.

Frequently asked questions

Will I lose my parking space

Yes, in the sense that the garage will no longer function as covered parking, though the driveway in front typically remains usable for parking a car. Some London boroughs place conditions on retaining off-street parking, which we check as part of your survey.

Can I convert a garage into a bedroom

Yes, provided the space meets Building Regulations for a habitable room, including minimum ceiling height, natural light, ventilation and fire escape provisions. Most integral and attached garages can meet these standards with the right insulation and window specification.

How long does a garage conversion take

A basic conversion typically takes 2 to 4 weeks on site. A more involved scheme with a bedroom and ensuite can take 8 to 12 weeks including first-fix plumbing and full finishing.

Does a garage conversion need an architect

Most straightforward integral and attached garage conversions do not need a full architectural service. We produce the Building Regulations drawings as part of our package, and only bring in an architect for more complex or detached garage schemes.

Book a free survey and find out what your garage could become, with a fixed quote back to you within 48 hours.