Garage Conversion Guide: Everything You Need to Know

Why Convert Your Garage?

A garage conversion is one of the most cost-effective ways to add usable living space to your home. Many homeowners in Surrey and London use their garages primarily for storage rather than parking. Converting this space can create a home office, gym, playroom, living room, or self-contained annexe at a fraction of the cost of a full extension.

Costs in Surrey (2025)

Single garage conversion: £15,000 – £25,000

Double garage conversion: £25,000 – £40,000

Garage to annexe (with plumbing): £25,000 – £45,000

These costs include structural modifications, insulation, damp proofing, flooring, electrics, plastering, and decoration.

Planning Permission

Most garage conversions fall under Permitted Development and do not require planning permission, provided:

The conversion does not extend the building's footprint

The property is not in a conservation area (some restrictions may apply)

The external appearance is not significantly altered

There are no conditions on the original planning permission restricting garage use

Building regulations approval is always required, regardless of planning permission status.

Building Regulations Requirements

Key building regulations for garage conversions include:

Structural integrity: Floor, walls, and roof must meet current standards

Insulation: Walls, floor, and roof must be insulated to meet thermal performance requirements

Damp proofing: A damp-proof membrane is required for the floor and sometimes walls

Ventilation: Adequate ventilation must be provided

Fire safety: Fire-rated doors may be required between the conversion and the main house

Electrical safety: All wiring must meet current Part P regulations

Popular Conversion Ideas

Home Office — increasingly popular for remote workers, providing a dedicated, separated workspace

Home Gym — eliminates gym memberships and commuting time

Cinema Room — soundproofed entertainment space for the whole family

Playroom — safe, dedicated space for children's activities

Self-Contained Annexe — ideal for elderly relatives or rental income (may need planning permission)

Grand Innovations' Garage Conversion Process

We follow a structured process for every garage conversion:

Free initial assessment — we visit your property, assess the garage, and confirm PD rights

Design proposal — detailed plans showing the conversion layout and specification

Building regulations application — we handle all compliance requirements

Construction — our team completes the conversion, typically within 3–5 weeks

Sign-off — building control inspection and completion certificate

Our weekly billing model means you pay only for completed work. No large deposits, no financial surprises.

Garage Conversion Guide: Everything You Need to Know