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Prices assume an insulated, year-round room: the GBP 300/m2 summerhouse is a different (three-season) product. Base and groundworks are usually included in fitted prices: check. Permitted development typically allows garden buildings up to 2.5m tall within 2m of a boundary, covering no more than half the garden: not for sleeping in, and conservation areas differ.
What The Garden Room Cost Calculator Works Out
- Estimated total: floor area multiplied by the rate for your route, plus the electrical connection. DIY insulated kits start around GBP 800/m2, supplied-and-fitted mid-market rooms run GBP 1,200 to GBP 1,800 including base, and premium turnkey builds with cedar cladding and aluminium bifolds pass GBP 2,000. The popular 12 m2 office therefore lands between GBP 10,000 and GBP 27,000.
- Electrics: the trench, armoured cable and consumer unit job is the near-universal extra at GBP 1,000 to GBP 2,000, and must be signed off by a Part P electrician.
- The 2.5m rule: permitted development allows outbuildings without planning where the overall height stays under 2.5 m within 2 m of a boundary (4 m with a dual-pitched roof further in), coverage stays under half the garden and the use is incidental, not a bedroom. Conservation areas and listed settings differ.
- vs the commute it replaces: the room undercuts a comparable extension by half or more because it skips foundations-grade groundworks, structural tie-ins and most professional fees.
- Base and groundworks (advanced): fitted prices usually include a concrete or ground-screw base, but kit prices rarely do. Budget about GBP 120/m2 if it is not in the quote.
- Heating and internet (advanced): a panel heater around GBP 250 or an air-conditioning heat pump that heats and cools around GBP 1,500; a wireless bridge about GBP 150 or a buried data cable about GBP 300 if the house wifi will not reach.
- Water and waste (advanced): a loo or sink needs a water supply and a drain run to the house, often GBP 1,500 to GBP 4,000 depending on distance, and brings Building Regulations fully into play.
- Grand total (advanced): everything added together and shown per square metre, the figure to put against a loft conversion or extension.
- Commute saving and payback (advanced): your daily fares or fuel x days worked from the room x 46 working weeks, and how many years of that saving repay the build. A GBP 15 daily commute three days a week saves about GBP 2,070 a year.