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Supported projects → Garden room / home office
A timber-frame garden room on a fresh slab, roofer rolling out the rubber roof membrane
garden room · provisional

Garden room / home office: how it is priced

An insulated, heated garden building on a slab for an office, gym or studio. Timber frame is typical; the power run from the house and the base are the items people forget.

FICTIONAL WORKED EXAMPLE · 4m × 3m (external) · 8.2 m² internal · finish: complete
£45,964.80
inc. VAT at 20% · £38,304.00 before VAT · about £4,694.12/m² · roughly 4 weeks on site
Materials (63 lines, catalogue allowances dated 2026-09-24)£14,757.95Labour (401 person-hours at a blended £30/hr)£12,025.20Provisional allowances (3)£1,800.00Plant£380.00Overheads 10% + contingency 5%£4,344.48Profit (15% markup)£4,996.14
WHERE THE MONEY GOES (AT COST)
External walls£9,525.65Roof£3,883.10Windows & external doors£3,320.00Excavation & foundations£1,714.40Floors£1,618.40Internal finishes£1,524.15Electrical£1,360.00Drainage£1,130.00

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. Dimensions — Are these internal or external measurements?, Length — depth, Width — width, Wall height to eaves
  2. Roof — Roof type, Pitch, Covering, Rooflights
  3. Walls — Wall construction, Outside finish
  4. Ground and foundations — Foundation type, Foundation depth, Ground, Floor construction…
  5. Windows and doors — Openings
  6. Site — Rainwater, Access
  7. How far do you take it? — Stage of completion, Specification level
  8. Electrics, heating and plumbing — Sockets and switches, Light fittings, Heating, Plumbing
  9. Inside finishes — Plastering, Flooring, Decoration, Internal doors…
  10. Inclusions, exclusions and notes — Exclusions, Notes for the estimate

Assumptions this example carries

  • Under 2.5m high at the eaves and within permitted development limits; building regulations apply if over 30 m² or with sleeping accommodation.
  • Foundations: trench fill 600mm wide × 0.6m deep in GEN1 concrete under all new external walls.
  • Ground floor: 100mm concrete slab on 150mm compacted hardcore with 100mm PIR insulation.
  • External walls: manufacturer-designed timber frame with insulated studs, breather membrane and a masonry or clad outer skin. The frame price is an allowance until the manufacturer quotes.
  • Flat roof: warm-deck construction with 120mm PIR, 47×195 C24 joists at 400 centres with firrings to fall, epdm rubber roof membrane with adhesives & trims.
  • Rainwater to a new soakaway at least 5m from the building; a percolation test may be required by building control.
  • The existing consumer unit has spare capacity for the new circuits; if not, a new unit is extra.

Priced work packages

Preliminaries & site setup · Site preparation · Excavation & foundations · Floors · External walls · Roof · Windows & external doors · Electrical · Plumbing & heating · Insulation & internal linings · Internal finishes · Scaffold & access · Plant hire · Waste removal · Deliveries · Testing & certification

Provisional sums

  • Timber frame kit (if chosen)
  • Power supply from the house (armoured cable run)

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
  • Decking and paths

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