The pandemic permanently changed the way Somerset homeowners think about their outdoor space. Demand for properly built garden rooms, home offices, detached garages and annexes is at an all-time high in 2026. But there is a significant difference between a flat-pack structure dropped in by a garden room company and a purpose-built outbuilding constructed properly by a building contractor. This guide explains both — and what you should actually expect to pay.
Flat-Pack Garden Room vs Properly Built Outbuilding — What Is the Difference?
The market is flooded with garden room companies offering structures from £8,000–£25,000. These are typically timber-framed, clad with composite boarding, and installed on adjustable pedestals or a minimal base. They are fine for a studio or occasional use space. But they are not insulated to building regulation standard, they are not designed to be used as habitable accommodation year-round, and they add limited value to your property. A brick-built or properly framed outbuilding with correct foundations, insulation and electrical installation is a permanent structure — it adds real measurable value to your property and can be converted or extended in the future.
2026 Outbuilding Cost Guide — Somerset
| Structure Type | Size | Price Range |
|---|---|---|
| Timber framed garden room (properly insulated) | 15–25m² | £18,000 – £35,000 |
| Brick-built garden room / studio | 15–25m² | £25,000 – £45,000 |
| Single brick-built garage | 20–25m² | £18,000 – £32,000 |
| Double brick-built garage | 40–50m² | £30,000 – £55,000 |
| Oak frame cart lodge / garage | 30–50m² | £35,000 – £70,000 |
| Self-contained annexe (fully habitable) | 40–60m² | £55,000 – £110,000 |
Do You Need Planning Permission for an Outbuilding in Somerset?
Most outbuildings in Somerset fall under Permitted Development (Class E) provided they meet size, height and use criteria. Key rules: the outbuilding must not be used as habitable accommodation (if it is, it is an annexe and requires planning), must not exceed 4m ridge height (2.5m within 2m of a boundary), and must not cover more than 50% of the garden. Conservation areas, listed properties and Areas of Outstanding Natural Beauty (AONB) have additional restrictions. We advise on this as part of every free initial site visit.
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