Garden office vs home extension: an honest comparison
Most people asking about a garden office have also had an extension quoted. They solve overlapping problems in very different ways, so here is the comparison without the sales pitch.
Cost per square metre
A single-storey rear extension in London and the South East typically runs £2,800–£4,500 per square metre before VAT, kitchen or bathroom fit-out. An insulated garden room of the same footprint is usually £2,000–£3,200 per square metre all-in. On a 15m² space, that difference is often £15,000–£20,000.
Build time and disruption
Extensions mean scaffolding, structural openings, dust inside the house and, frequently, twelve to twenty weeks of works. A garden room is built away from the house: two to four weeks on site, no internal wet trades, and the kitchen stays usable throughout. If you work from home, that difference matters more than the money.
Planning permission
Both can usually be done without a full application, but the routes differ. Extensions rely on permitted development limits for depth and height, and larger rear extensions need Prior Approval with a neighbour consultation. Garden rooms are incidental outbuildings: single-storey, 2.5m maximum height within 2m of a boundary, and under 50% garden coverage. Neither route applies automatically in conservation areas.
When an extension is the better choice
Choose the extension if you need connected internal space — a bigger kitchen, an extra bedroom counted in the floor area, or a downstairs bathroom. Surveyors value internal floor area more readily than outbuildings, so if resale value is the primary driver an extension has the edge.
Choose the garden room if you need a quiet, separate space for work, training, music or guests, and you want it finished this quarter rather than next year.
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