Build wooden structures.

Building a timber structure in the UK — a garden room, log cabin, summerhouse, pergola, or framed annexe — typically costs £3,000–£35,000, depending on size, whether it's habitable, and the level of insulation and finishes. Smaller decorative pieces (pergolas, lean-tos) start at £800; insulated garden offices in the £15,000–£25,000 bracket are now the most common ask.

Timber structures in domestic gardens often fall under permitted development, but only if they're outbuildings (no residential use), under 2.5 m at the eaves if within 2 m of a boundary, and don't cover more than 50% of the garden area.

Typical UK costs by structure type

What's typically in the build

• Foundations — concrete pad foundations, ground screws, or paved base. Ground screws are increasingly popular for garden offices: faster, less digging, no concrete cure time.
• Sub-floor and wall frame — pressure-treated timber frame on the foundation, with insulation between studs (rockwool, PIR, or sheep's wool).
• Cladding — typically tongue-and-groove softwood (pre-treated or stained), Western Red Cedar (low-maintenance, premium), or composite cladding (no maintenance, premium).
• Roof — pitched (felt or shingle on ply) or flat (EPDM rubber, single-ply membrane). EPDM has become the standard for flat roofs — 20+ year service life with virtually no maintenance.
• Glazing — double-glazed windows and doors are standard for habitable structures. Bi-folds or sliders for the main view; opening side windows for ventilation.
• Electrics — armoured cable from the house consumer unit, RCD-protected. £600–£1,500 for a typical garden-office spec.

Insulation — the big spec decision

For a non-habitable summerhouse, no insulation is fine — it's a fair-weather space. For a year-round garden office, insulation makes the difference between usable and miserable. Options:

• PIR boards (Celotex / Kingspan) — high R-value per mm, used in walls, roof and floor. Adds 50–100 mm to wall thickness.
• Rockwool / mineral wool — cheaper, fits between studs, slightly worse U-values for the same thickness.
• Sheep's wool — sustainable, breathable, similar U-values to rockwool, more expensive.

Target U-values: walls 0.20 W/m²K, roof 0.15 W/m²K, floor 0.20 W/m²K. Hitting these allows a small electric heater to keep the room warm with low running costs.

Things people often miss

• Permitted development limits — eaves height (2.5 m within 2 m of boundary, 4 m otherwise), maximum floor area covering 50% of garden, no residential use. Exceeding any of these means full planning permission.
• Habitable vs non-habitable — sleeping in your garden office is normally not permitted under outbuilding rules. Granny annexes need full planning + Building Regs and cost considerably more.
• Damp-proofing under the floor — DPM under the deck or insulated floor void prevents rising damp. Often skipped on cheap builds; the structure rots from the floor up within 5–8 years.
• Cladding maintenance — softwood cladding needs treating every 2–4 years. Cedar weathers to silver-grey but resists rot for 20+ years untreated. Composite cladding needs no maintenance but costs 2–3× softwood.
• Heating + ventilation — insulated buildings need ventilation. A small MVHR unit or a passive vent grille per room prevents condensation. Trickle vents on the windows are usually enough for a single-room garden office.
• Building Regs threshold — outbuildings under 30 m² with no sleeping accommodation are typically exempt from Building Regs. Over 30 m² or with sleeping use, full Building Regs apply.

Frequently asked questions

Want a local pro to handle this? A timber-frame specialist or experienced carpenter will deliver a structure that lasts 25+ years rather than 10. Check their portfolio for the type of build you want — a garden office is a different skill from a pergola or carport.