Converting a garage is one of the most cost-effective ways to add usable living space to a house. Unlike an extension, the structure already exists — you’re fitting out rather than building from scratch. A single integral garage of 15–20 m² can become a bedroom, home office, playroom, or utility room for significantly less than the equivalent extension would cost, and in most cases with no planning permission required.
This guide covers realistic 2026 costs, planning rules, insulation requirements, floor level issues, and the most practical conversion ideas.
Cost Overview
Garage conversion costs depend on the condition of the existing structure, the level of fit-out, and what the converted space will be used for. A basic conversion (insulated, plastered, with lighting and heating) runs cheaper than a full en-suite bedroom conversion.
Single Garage Conversion Costs (15–20 m², UK 2026)
| Specification | Cost range |
|---|---|
| Basic (insulated walls/roof/floor, plastered, lit) | £8,000–£12,000 |
| Mid-range (+ electrical circuits, radiator, new window/door) | £12,000–£17,000 |
| Bedroom with en-suite | £16,000–£25,000 |
| Home office with fitted furniture | £14,000–£22,000 |
| Full kitchen (utility/ancillary) | £15,000–£24,000 |
Double garage conversions roughly double the above, though economies of scale apply on groundworks and insulation. Budget £18,000–£40,000 for a double garage to usable habitable space.
What the Price Includes
A typical builder’s quote for a garage conversion covers: removal of the garage door and wall, blockwork infill, insulated stud partitions or direct insulation to walls, new external door and/or window, insulation to floor and roof/ceiling, first and second fix electrics, one or two radiators, and plastering. It generally excludes: kitchen or bathroom fitting, floor finishes, decoration, furniture, and sometimes the building control application fee (typically £150–£400).
Always clarify what’s included — a quote of £9,000 that excludes the floor insulation, floor finish, and decoration may end up costing £14,000 once those items are added.
Planning Permission and Permitted Development
Most integral and attached garage conversions in England do not require planning permission. Converting the interior of an attached or integral garage (one that is structurally part of the house, sharing at least one wall) is generally permitted under Class A permitted development, since it doesn’t create a new external volume.
Exceptions where planning permission is required:
- Detached garages: Converting a detached outbuilding to habitable use is a change of use and may require permission, particularly if it creates an independent dwelling unit
- Conservation areas and Article 4 Directions: Some local authorities remove PD rights for garage conversions in sensitive areas — check before starting
- Listed buildings: Listed building consent required for any internal or external alterations
- Properties where PD was removed as a condition of the original planning permission (common on newer estates)
One common condition on housing estates is a covenant or planning condition requiring the garage to remain as a garage. Check your title deeds and the planning history of the property before proceeding.
Building Regulations always apply to a garage conversion. You’ll need approval under Parts A (structure), B (fire safety), F (ventilation), L (energy efficiency), and P (electrics). Your builder should handle the building control application; if they don’t, apply to your local authority building control (LABC) or an approved inspector.
Insulation
A garage built in the 1970s–1990s typically has a single-skin block wall, an uninsulated concrete floor, and a thin flat or pitched roof with minimal insulation. To convert it to a habitable room, all three elements need upgrading to meet Part L of Building Regulations (Conservation of Fuel and Power).
Walls
Internal insulated dry-lining is the standard approach. A 65–75 mm PIR board (e.g., Celotex GA4000 or Kingspan Kooltherm) bonded to the internal face of the block, overboarded with plasterboard, achieves a wall U-value of around 0.22–0.25 W/m²K — sufficient for Part L compliance. This loses approximately 80–100 mm on each treated wall.
Alternatively, a timber stud frame with 100 mm mineral wool batts and a vapour control layer achieves a similar result at marginally lower material cost but greater depth loss (120–150 mm).
For an external single-skin wall, the minimum effective insulation to avoid condensation and cold bridging is 60 mm PIR with a foil-taped VCL on the warm face.
Floor
Garage floors are typically 100–150 mm of reinforced concrete slab, often at a lower level than the house internal floor (see section below). Insulation goes above the slab: 75–100 mm of PIR board (e.g., Celotex PL4000) gives a floor U-value of approximately 0.18–0.25 W/m²K. Over this goes a screed or floating timber deck.
The floor build-up reduces the finished floor level: 75 mm PIR + 50 mm screed = 125 mm, or 75 mm PIR + 18 mm chipboard floating deck = 93 mm. This is relevant to the floor level issue discussed below.
Roof and Ceiling
If the garage has a flat roof, 150 mm of PIR above the roof deck (warm flat roof construction) achieves approximately 0.15 W/m²K. A cold-loft configuration (insulation between joists at ceiling level) at 200 mm mineral wool achieves approximately 0.16 W/m²K.
Pitched garage roofs are easiest to insulate at rafter level with 100–150 mm PIR spray-fixed between and below rafters.
Floor Level Considerations
The most common technical complication in garage conversions is that the garage floor is typically 100–200 mm lower than the house’s internal floor level, to allow drainage of water from vehicles.
Options for managing the level difference:
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Raise the garage floor to match: Add a new floor build-up (insulation + screed or floating deck) to bring the level up. This works when there is sufficient headroom (minimum 2.1 m finished ceiling height required under Building Regulations — 2.3 m is more comfortable). Loss of 125–200 mm of height must be checked against your existing soffit level.
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Step down: Accept a step at the threshold between house and garage. A single 100–150 mm step with a threshold strip is manageable for most uses but rules out level-access requirements and is not ideal for mobility.
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Lower the slab: Break out the existing concrete, excavate, and re-pour at the required level. Cost: £2,000–£4,500 depending on area and access. Rarely necessary but sometimes the only solution for low-headroom garages.
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Floating timber deck: A timber joist deck over the existing slab, with insulation fitted between joists, raises the floor by 200–250 mm but avoids the weight and cure time of screed. Less suitable for a wet room use case.
Always measure headroom before committing to a conversion — minimum habitable ceiling height under Building Regulations is 2.1 m (measured to the finished ceiling). Low-headroom garages (original internal height under 2.3 m) may not be viable for conversion to a full room.
Ideas: Best Uses for a Converted Garage
Home Office
The most popular conversion use in 2026. A garage typically offers 15–20 m², enough for a generous desk setup, storage, and a meeting area. The separation from the main house is a productivity benefit. Key requirements: good broadband route to the garage (consider Cat6 cable run at build stage), sufficient electrical circuits, and ideally a separate entrance. For the self-employed, capital allowances or business use of home deductions may apply.
Bedroom (Including Guest Room)
An en-suite bedroom conversion is the use that adds most to a property’s valuation — typically adding 5–10% to resale value on a 3-bed house. Requirements: window of appropriate size for natural light and escape (generally minimum 0.33 m² opening area for a habitable room), ventilation, heating, and an accessible route. Building control will check these.
Playroom / Family Room
Lowest-cost conversion option since the fit-out is minimal. Requires insulation and heating but not kitchen or bathroom provision. A good use for a garage with a floor level step, as children’s spaces are forgiving of level changes.
Utility and Boot Room
Adding a utility room adjacent to the kitchen (for washing machines, tumble dryers, NAS storage, and boot/coat storage) typically doesn’t require full habitable-space insulation standards — though in practice it’s worth insulating properly to avoid condensation issues. This is the cheapest conversion category.
Annex or Dependent Relative Accommodation
If the conversion includes sleeping, washing, and cooking facilities (a separate dwelling), planning permission is likely required as this is a material change of use. Building Regulations apply in full, and the design must meet accessibility requirements (Part M) if the annex is likely to be used by someone with mobility needs.
Finding a Builder
Garage conversions don’t require specialist contractors — most general builders with renovation experience can handle a straightforward integral conversion. Get three quotes and ensure each covers: building control application, all groundworks, structural infill to the garage opening, insulation to walls/floor/ceiling, first and second fix electrics, and any drainage if adding a bathroom.
Avoid any builder who suggests omitting building control — a conversion without sign-off will create problems when you come to sell the property.
