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Supported projects → Garage conversion
A carpenter fixing insulated plasterboard inside a garage being converted, new window where the door was
conversion · provisional

Garage conversion: how it is priced

Turning an existing garage into a habitable room: infill the door, upgrade the floor, insulate and line the walls and roof, then heat, wire and finish. Attached or detached.

FICTIONAL WORKED EXAMPLE · 5.5m × 3m (internal) · 16.5 m² internal · finish: complete
£18,280.80
inc. VAT at 20% · £15,234.00 before VAT · about £923.27/m² · roughly 2 weeks on site
Materials (33 lines, catalogue allowances dated 2026-09-24)£4,707.50Labour (189 person-hours at a blended £30/hr)£5,661.45Provisional allowances (2)£1,150.00Plant£0.00Overheads 10% + contingency 5%£1,727.85Profit (15% markup)£1,987.02
WHERE THE MONEY GOES (AT COST)
Internal finishes£2,435.00Insulation & internal linings£2,130.95Windows & external doors£1,200.00External walls£920.00Fees & approvals£900.00Electrical£856.00Floors£766.50Plumbing & heating£653.00

Open the full line-by-line example →

Default answers, a blended £30/hr labour rate and dated catalogue allowances. Your job, your rates and your merchant prices will differ — that is the point of the tool. Templates marked provisional are being validated against measured projects; every estimate says so.

What the wizard asks

  1. The existing garage — Is the garage attached to the house?, Garage door opening width, Existing garage walls, Existing roof
  2. Dimensions — Are these internal or external measurements?, Length — length, Width — width, Ceiling height
  3. Windows and doors — Openings
  4. How far do you take it? — Stage of completion, Specification level
  5. Electrics, heating and plumbing — Sockets and switches, Light fittings, Heating, Plumbing
  6. Inside finishes — Plastering, Flooring, Decoration, Internal doors…
  7. Inclusions, exclusions and notes — Exclusions, Notes for the estimate

Assumptions this example carries

  • Existing slab is sound and level; a damp-proof membrane, 100mm insulation and a new deck are laid over it.
  • Existing flat roof is sound; 120mm insulation added between/under joists and a new ceiling.
  • The existing consumer unit has spare capacity for the new circuits; if not, a new unit is extra.
  • Heating: 2 radiators added to the existing system; the existing boiler is assumed to have capacity.
  • No planning application fee, party wall surveyor or planning drawings are included. Permitted development or existing consent is assumed.
  • Work to comply with the building regulations applying in England; design by others where a design is required.
  • Garage door infill to match existing brickwork; a matching brick is assumed available.

Priced work packages

Preliminaries & site setup · Excavation & foundations · External walls · Windows & external doors · Floors · Electrical · Plumbing & heating · Insulation & internal linings · Internal finishes · Kitchen & bathroom · Waste removal · Deliveries · Testing & certification · Fees & approvals

Provisional sums

  • Damp-proofing where the existing slab has no membrane
  • Roof insulation if the existing roof cannot take it
  • Structural work if the garage wall is single skin

Not included

  • Planning application, drawings and party wall matters
  • Furniture, appliances and loose fittings
  • Landscaping and reinstatement beyond the working area
  • Anything found on opening up that could not be seen at survey
  • Repairs to the existing roof or walls

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