A garage extension — either adding a new integrated garage to your house or extending an existing detached or attached garage — is one of the more practical additions a homeowner can make. Beyond car storage, a well-built garage extension can house a workshop, gym, utility room, or serve as a platform for habitable space above. The cost range is wide because the spec can vary enormously, from a basic blockwork single-car garage to a steel-framed double with a room in the roof.
Typical Cost Ranges (2026)
| Project | Budget | Mid-Range | High Spec |
|---|---|---|---|
| Single garage (attached, blockwork, up-and-over door) | £18,000 | £26,000 | £40,000 |
| Double garage (attached, blockwork, two doors) | £28,000 | £42,000 | £60,000+ |
| Single garage (detached, slab foundation) | £22,000 | £32,000 | £48,000 |
| Double garage (detached) | £35,000 | £52,000 | £75,000+ |
| Garage with room above (integrated) | £45,000 | £70,000 | £110,000+ |
These figures include foundations, blockwork walls, roof structure, roofing material (concrete tiles), insulation, electrical first fix, garage door, plastered internal walls, and concrete floor. They do not include fitted interiors, bespoke doors, planning fees, or architect fees.
London and South East prices typically run 20–35% above these figures. Scotland and Wales are broadly similar to the national mid-range.
What Drives the Cost
Foundation Type
- Strip foundations — most common for attached garages on stable ground; 450–600 mm wide, 150–225 mm deep concrete trench; excavation and concrete runs £3,000–£6,000 for a single garage
- Raft foundation — used on poorer ground (clay, made ground); reinforced concrete slab over the whole footprint; add £2,000–£5,000 versus strip
Wall Structure
- Cavity blockwork — 100 mm inner leaf, 75–100 mm cavity with full-fill insulation, 100 mm outer leaf; standard and Building Regs-compliant; labour and materials £180–£280/m² of wall
- Steel portal frame with cladding — faster to erect, span potential of 10 m+ without internal posts; popular for larger garages; cladding varies from profiled steel sheets (cheapest) to brick-clad for visual match with the house
- Timber frame (SIPs or stick-built) — faster on site, good thermal performance, favoured when the garage must match an existing timber-frame house
Roof Type
- Pitched (duo-pitch or mono-pitch) with concrete tiles — most common; higher cost but matches the house; insulation can go above or at ceiling level
- Flat roof (warm deck) — lower build cost; more suited to rooms above; modern EPDM or GRP covering with 120 mm PIR insulation
- Green roof — increasingly used where planning policy requires visual softening; add £80–£150/m² over a standard flat roof
Garage Door
| Type | Typical Supply Cost | Notes |
|---|---|---|
| Up-and-over (steel) | £400–£900 | Most common, budget option |
| Sectional (insulated panel) | £900–£1,800 | Better thermal performance |
| Roller (insulated) | £800–£1,600 | Space-saving; suits narrower openings |
| Side-hinged (timber) | £700–£2,000 | Traditional look; suits rural/period homes |
| Electric operation (add to any type) | £300–£600 extra | Worth specifying from the start |
Planning Permission
Permitted Development (Attached Garage)
An attached garage extension that forms part of the dwelling is treated as a house extension under Class A of the GPDO 2015. Key limits:
- Must not exceed the original house volume by more than 50% (the cumulative rule)
- Single-storey extension at rear: maximum 4 m beyond original rear wall (detached house) or 3 m (semi/terrace) under standard PD; up to 8 m/6 m under the Neighbour Consultation Scheme
- Maximum height of single-storey extension: 4 m
- Extension on a side elevation adjacent to a highway: not PD
Side extensions are excluded from PD on corner plots or where the side elevation fronts a highway.
Detached Garage (Outbuilding)
A detached garage is assessed under Class E (outbuildings):
- Maximum footprint of all outbuildings: 50% of the curtilage (excluding the original house footprint)
- Maximum height: 4 m (dual-pitched roof) or 2.5 m within 2 m of a boundary
- Must not be forward of the principal elevation
Most single and double detached garages fall within PD. If in doubt, apply for a Lawful Development Certificate (£234 planning fee in England, 2026).
When Planning Permission Is Required
- Conservation areas (any extension to an existing house, and detached outbuildings over 10 m²)
- Listed buildings (Listed Building Consent required)
- Any garage with a room above that counts as additional habitable accommodation
- Schemes exceeding PD thresholds
Building Regulations
A garage extension always requires Building Regulations approval unless it is a small (under 30 m²) detached structure with certain conditions. Key parts:
- Part A (Structure) — foundations, walls, and roof must be structurally adequate
- Part B (Fire) — if the garage connects to the house, the connecting door must be self-closing and fire-resistant; the floor of the garage must be lower than the house (minimum 100 mm threshold) to prevent fuel spread
- Part F (Ventilation) — minimum ventilation if habitable space is above or within
- Part L (Energy) — insulation to current standards if the space is heated or if habitable use is above
- Part P (Electrical) — any new circuits require notification and testing by a competent person
Design Ideas
Integrated Garage with Studio Above
Popular on larger plots; the ground floor handles cars and storage while the upper level provides a home office, gym, or guest annex. Requires planning permission and full Building Regs compliance including fire separation, means of escape, and insulation. Budget £70,000–£110,000 for a complete two-storey attached structure.
Garden Room / Workshop Hybrid
A garage with a workshop area to one side, insulated internal walls, and power — increasingly popular as working from home continues. The key is running 25 A (or 40 A) electrical supply from the consumer unit for power tools and EV charging, budgeted separately at £1,500–£4,000.
Car Port Instead of Full Garage
An open-sided carport costs significantly less than a walled garage: expect £6,000–£14,000 for a steel or timber post-and-beam structure with a lean-to or flat roof over two car widths. Falls under outbuilding PD rules more readily.
Getting Quotes
Always obtain a minimum of three quotes from contractors who can show recent comparable work. Specify in your brief:
- Foundation type you expect (let them advise if uncertain)
- Brick or render finish to match the house
- Level of insulation (ask for U-values)
- Electrical provision required
- Whether Building Regs application is included
Architects or architectural technologists charge £1,500–£4,000 for garage drawings and building control submissions; for a standard single garage this is optional but helpful if planning permission is needed.
