Garage Conversion Costs in London: Full 2025 Price Guide
Garage conversions are consistently one of the most cost-effective ways to add habitable floor space to a London property. The structure already exists — conversion involves insulation, floor, electrics, and connection to the house, rather than building from scratch.
Types of Garage Conversion
Integral garage: Built into the house footprint, typically with a shared party wall or internal wall with the main house. Easiest and cheapest to convert — existing roof and three walls already part of the house structure.
Attached garage: Structurally connected to the house but with its own roof. Conversion involves insulating the walls and roof, installing a new floor, and creating or widening the connection to the house.
Detached garage: A separate structure. Conversion may be viable for home office or ancillary uses but connection to the main house heating and services is more complex. Not covered in detail here.
What Does a Garage Conversion Involve?
The typical scope of a garage conversion to a habitable room:
- Floor: Remove concrete slab or garage floor; install DPM, insulation, new screed or floating floor
- Walls: External walls insulated internally (or externally if block construction); internal lining with insulated plasterboard
- Roof: Insulated to current Building Regulations standard (if flat roof, warm roof insulation; if pitched, ceiling insulation or rafter insulation)
- Opening: Garage door opening in-filled with insulated wall, window, and door if required
- Electrics: First-fix wiring for lighting, sockets, and potentially heating circuit
- Heating: Radiator connected to main heating system, or alternative heating provision (underfloor, electric)
- Plumbing: If a WC or en-suite is being added, soil and waste connection
- Building Regulations: Application required; inspections at key stages
Typical Costs in London (2025)
| Scope | Approximate cost |
|---|---|
| Basic integral garage conversion (habitable room, no wet room) | £12,000–£18,000 |
| Standard integral garage to bedroom + en-suite | £18,000–£28,000 |
| Attached garage conversion (more complex) | £20,000–£35,000 |
| Garage + side infill extension combined | £35,000–£55,000 |
Costs depend on size (single vs. double garage), specification, whether a wet room is included, and the quality of finishes.
Planning Permission
Most integral and attached garage conversions are permitted development — planning permission is not required if:
- The property is not in a conservation area (where Article 4 may remove PD rights)
- The conversion does not alter the external appearance (simply in-filling the garage door opening typically complies)
- The number of dwellings on the site is not increased
Where the garage door opening will be replaced with a window or clad in a different material, check whether planning permission is required — particularly in conservation areas.
Building Regulations
Building Regulations approval is required for all garage conversions. Key areas:
- Thermal insulation to meet current Part L standards
- Means of escape if the room will be a bedroom
- Fire safety (particularly if the garage adjoins the house — fire separation between garage and habitable space must be improved)
RCB Design & Build
RCB Design & Build delivers garage conversions across London — from basic room conversions through to garage + extension packages.