The Cellar

Every Arden & Oak garden room is stick-built from a C16-treated structural timber frame — 4″ × 2″ to the walls and floor, 6″ × 2″ to the roof. Sometimes we panelise the frame in our workshop for a cleaner, quicker install, but the construction method is the same. Precision-cut in the UK and delivered ready to assemble.

From outside in: premium cladding → battens & counter-battens (ventilated cavity) → breather membrane → 12mm OSB sheathing → C16 4″ × 2″ stud frame with 90mm PIR insulation between studs → internal vapour control layer → plasterboard & skim finish. The roof build-up: EPDM rubber membrane over 18mm OSB on C16 6″ × 2″ rafters, with 90mm PIR between rafters and a 50mm ventilation gap above, VCL and plasterboard & skim ceiling. Floor: 18mm moisture-resistant chipboard over VCL and 90mm PIR between C16 joists.

Independent thermal modelling shows our envelope retains heat up to 7× longer than a 70mm stud frame shed. A 1.5kW panel heater is typically enough for a 15m² office in mid-winter. Annual running cost for a year-round home office: ~£140 at 2026 electricity rates.

Standard finish is plasterboard with a hand-skimmed plaster surface, left to cure for 3–5 days before any decorating. Add the Turnkey option and our finishing team paints walls and ceiling in any Valspar colour, fits laminate flooring and installs skirting boards — your room arrives ready to use.

Survey & ground assessment (week 1) → M24 steel-anchored foundations set in concrete-filled post holes and levelled → timber frame erected and weather-tight in 3 days → second-fix electrics, glazing and finishing over a further 2–4 days. No full concrete slab, no skip. Helical ground screws are available as a paid upgrade if your plot calls for them.

10% deposit on order. 40% on factory production start. 40% on delivery to site. Final 10% on completion and snag sign-off. We don't broker finance — most customers fund their build through savings, a personal loan, home equity or business funding. See our funding guide at /funding-your-garden-room for a plain-English breakdown of each route.

Used wholly for business? Limited companies can claim Capital Allowances on the contents and services (electrics, heating, glazing) — typically 35–55% of the build cost. VAT is reclaimable. The structure itself remains personal asset, so no Capital Gains issue on house sale.

Do I need planning permission? — Most builds fall under Permitted Development (under 2.5m eaves, no closer than 2m to a boundary at full height). Can it run plumbing? — Yes, with mains feed from the house. Lead time? — 6–8 weeks from deposit to install.

We install across England and Wales. Standard delivery covers everywhere within 250 miles of our Devon workshop; further north (above Manchester) carries a £450 logistics supplement. Scotland and Northern Ireland by quotation.