Forest Xtend 4.0 Insulated Garden Office 4.05m x 3.42m

The Forest Xtend 4.0 is a fully insulated SIP-built garden office measuring 4.05m x 3.42m (13ft 3in x 11ft 3in) externally. XTEND4.0HDBUN gives you 3.67m x 2.68m of usable internal floor space enough for a proper home office setup. That is nearly 10 square metres of insulated working space.

Walls are built from 97mm SIP panels 75mm polystyrene sandwiched between two OSB sheets with 15mm tongue and groove external cladding and MDF internal cladding. Total wall thickness hits 177mm. The 108mm SIP floor and 122mm SIP roof mean insulation runs top to bottom. Outside, a 1.2mm EPDM rubber membrane covers the pent roof UV-stabilised and maintenance free with a 50-year life expectancy.

A double-glazed uPVC door with a 7-point multi-lock and Ultion Three Star Security Barrel secures the building. Three full-length 28mm A-rated double-glazed windows flood the interior with light. One side window opens for ventilation. Wall battens create cavities for electrical wiring and 45mm roof battens allow recessed lighting.

A 15-year structural guarantee backs the build. It arrives untreated and flat packed in pre-cut modular panels. Energy efficiency rating is 78 (category C) with potential to reach 82 (category B).

The Xtend 4.0 uses SIP panel construction throughout. Each wall panel is 97mm thick 75mm polystyrene insulation between two OSB sheets. With 15mm tongue and groove external cladding and MDF internal cladding on 28mm battens the total wall build-up reaches 177mm. The 108mm SIP floor and 122mm SIP roof extend the insulation envelope to every surface. Outside, a 1.2mm EPDM rubber membrane covers the pent roof UV-stabilised, it will not crack, split or support moss growth and carries a 50-year life expectancy. All glazing is 28mm A-rated double-glazed safety glass in uPVC 5-chamber frames.

Structure: SIP panels with 75mm polystyrene core between two OSB sheets. External cladding: 15mm kiln-dried tongue and groove timber. Internal lining: primed MDF with vertical beaded profile. Floor: 108mm SIP panel, uncovered. Roof: 122mm SIP panel with 1.2mm EPDM rubber membrane. Doors and windows: uPVC 5-chamber reinforced frames with 28mm A-rated double-glazed safety glass.

A solid level concrete slab or paving base is required before installation. The base must cover the building footprint of 4.03m x 3.04m at minimum. No base is supplied. The buyer is responsible for preparing the ground before the delivery or installation date.

The Xtend 4.0 arrives flat packed in pre-cut modular SIP panels. All fixtures, fittings, anthracite grey fascias and a step-by-step installation guide are included. Two people can complete the build over a weekend. The pre-cut panels are designed for straightforward assembly without specialist tools. Professional installation is available as an optional extra if preferred.

Forest offer a professional installation service carried out by expert fitters. A solid level base must be in place before the installation date. Installation does not include electrics or other accessories. Book the service as an optional extra when ordering.

Forest do not supply or fit electrics. The 28mm wall battens create a cavity for routing cables and the 45mm roof battens leave space for recessed lights. All electrical work must be carried out by a qualified electrician. No wiring is included.

Treat the exterior timber cladding on assembly then every year Forest recommend Sikkens Cetol HLS Plus, Osmo Country Colour or Restol Wood Oil. The EPDM roof needs no maintenance. Clean glazing as needed. Annual treatment is required to maintain the 15-year structural guarantee.

The internal floor space is 3.67m x 2.68m roughly 9.8 square metres. That comfortably fits two desks with room for a storage unit or shelving. As a single home office it gives you space for a large desk, monitor setup and a small sofa or meeting chairs. The full-length windows and 2400mm eaves height make it feel spacious. It also works well as a hobby room, art studio or home gym with space for a bench and free weights. The full insulation means it is practical for daily use all year round.

Most garden offices in England fall under permitted development and do not need planning permission if single storey and used ancillary to the main house. This model has an eaves height of 2400mm and a ridge height of 2500mm. Rules differ in Scotland, Wales and Northern Ireland. Always check with your local planning authority this is not legal advice.