Garage Conversion in London: Costs, Planning, and What to Expect

London has three main types of garage that homeowners convert:

**Integral garage**: Built into the main structure of the house, typically beneath a first-floor room. The most common type in 1930s–1970s semi-detached and detached houses in suburban London (outer boroughs). The easiest to convert because the structure is already part of the house.

**Attached (adjacent) garage**: A single-storey structure attached to the side or rear of the house, sharing one or more walls. Slightly more complex to convert because the roof and possibly the floor slab are not part of the main house structure.

**Detached garage**: Separate from the main house. Converting a detached garage to habitable accommodation is technically a change of use and is more complex from a planning perspective. Not covered in this guide — consult a planning consultant for detached structures.

**Permitted Development**: In most cases, converting an integral or attached garage to a habitable room falls within Permitted Development — no planning permission is required. The key conditions are:

- The works do not extend the footprint of the building - The change of use does not involve subdivision into a separate dwelling - The building is not in an area where PD rights have been removed

**When planning permission IS required**:

- **Conservation areas and Article 4 areas**: The removal of a garage door and its replacement with a wall, window, or door visible from a highway typically requires planning permission in conservation areas, as it changes the external appearance of the building. - **Garage door removal**: Even outside conservation areas, some councils have removed PD rights for garage conversions specifically (or for alterations to principal elevations). Always check. - **HMO conversions**: If the garage conversion is part of a wider HMO conversion, separate planning and licensing requirements apply.

A Lawful Development Certificate is strongly recommended for garage conversions even where planning permission is not required — it provides legal certainty and is required by solicitors on sale.

Building Regulations approval is always required for a garage conversion to habitable accommodation, regardless of whether planning permission is needed. The key Building Regulations elements are:

**Part A (Structure)**: The existing slab, walls, and roof must be structurally adequate for habitable use. The slab in particular may need upgrading or damp-proofing.

**Part B (Fire Safety)**: The converted garage must have adequate means of escape. In most integral garage conversions, the door between the garage and the hallway must be replaced with a fire door (FD30S) with appropriate self-closer.

**Part C (Resistance to Moisture)**: The existing floor slab typically has no damp-proof membrane (garages don't need one). A new damp-proof course must be installed under any new floor construction. Rising damp and condensation must be managed.

**Part F (Ventilation)**: Habitable rooms require adequate background ventilation (trickle vents in windows) and extract ventilation in any wet room elements.

**Part L (Energy Efficiency)**: The converted space must meet current thermal performance standards — typically U-values of 0.18 W/m2K for walls, 0.13 W/m2K for floors, and 1.4 W/m2K for windows. This almost always means upgrading the walls, floor, and roof of an existing garage.

**Part M (Access)**: Thresholds and doorways should be accessible where reasonably practicable.

**Electrical installation**: All new electrical work must comply with Part P and must be designed and certified by a registered electrician.

A typical integral or attached garage conversion in London involves:

1. **Structural assessment**: Checking the existing floor slab, walls, lintel over the garage door, and roof structure. Any deficiencies are addressed before conversion begins. 2. **Garage door removal**: The existing garage door and frame are removed. The opening is either partially infilled to create a window and wall below, or fully infilled where no window is required. 3. **New wall construction**: The infill panel is typically built in blockwork (matching the existing wall construction) with a new window opening to provide natural light and ventilation. 4. **Floor treatment**: The existing concrete slab is either overlaid with insulation and a new screed or timber deck, or broken out and replaced with an insulated ground floor slab meeting Part L requirements. 5. **Wall insulation**: Internal insulation (typically 75–100mm rigid foam or PIR board) is applied to the external walls to meet Part L thermal performance. 6. **Ceiling / roof**: If there is a room above (integral garage), the existing ceiling remains and may need upgrading for fire resistance and sound insulation. For attached garages, the roof space may be used to add insulation. 7. **First-fix services**: Electrical, heating (extension of existing system or new underfloor heating), and plumbing if a wet room is included. 8. **Second fix and finishes**: Plastering, flooring, joinery, decorating.

A garage conversion in London typically costs:

- **Basic garage conversion (no structural issues, no wet room, straightforward layout)**: £15,000–£25,000 - **Mid-range conversion (en-suite shower room, quality finishes)**: £25,000–£40,000 - **Higher-specification conversion (full bathroom, bespoke joinery, underfloor heating)**: £40,000–£60,000+

The main cost variables are: - **Floor treatment**: Overlaying an existing slab (lower cost) vs breaking out and replacing (higher cost but preferred where moisture is a concern) - **Wet room**: Adding a shower room or bathroom adds £5,000–£15,000 - **Structural issues**: Lintel replacement, crack repairs, underpinning if the slab has settled - **Garage door infill**: A well-detailed brick infill with window is typically £2,500–£4,500; render or cladding finish is an alternative - **Finish level**: Builder's finish vs fully decorated and furnished

Garage conversions typically add £20,000–£50,000 in value to a London property — a positive return in most cases where the garage was not being used productively for parking.

A straightforward garage conversion in London typically takes 4–8 weeks from start on site to practical completion. The sequence is:

- Weeks 1–2: Strip out, demolish, structural works, damp-proof floor treatment - Weeks 2–4: First-fix electrical and plumbing, wall insulation, new floor construction - Weeks 4–6: Plastering, second-fix electrical and plumbing, tiling if wet room included - Weeks 6–8: Decorating, flooring, final finishes, Building Control sign-off

Building Control inspection is required at key stages (foundation/floor before overlay, before plastering). The completion certificate is issued after the final inspection sign-off. This is an important document for future sale.