Forest Xtend 4.0+ Fully Insulated SIP Garden Room Office with UPVC Double Doors 4.05m x 3.42m

The Forest Xtend 4.0+ is a fully insulated SIP garden room measuring 4.05m x 3.42m (13ft x 11ft) externally. XTEND4.0PHDBUN gives you 3.67m x 2.68m of usable internal floor space enough for a proper home office setup. The SIP panel construction delivers 177mm total wall thickness with 97mm insulated core panels sandwiched between OSB sheets. External 15mm kiln-dried tongue and groove cladding sits alongside primed internal MDF with a vertical beaded profile.

The 108mm SIP floor and 122mm SIP roof mean insulation runs through the entire structure not just the walls. The EPDM rubber roof membrane has a 50-year life expectancy and will not crack, split or support moss growth. Anthracite grey fascias complete the exterior. The building arrives untreated and needs treating on assembly then annually.

UPVC double doors are secured by a 7-point multi-lock with Ultion three-star security barrel. Two full-length double-glazed windows with opening top halves bring in natural light and ventilation. All glazing is 28mm A-rated safety glass. Wall battens and 45mm roof battens allow cable routing for electrics by a qualified electrician.

A 15-year structural guarantee backs the build. The energy efficiency rating is 78 (category C) with potential to reach 82 (category B). It works year-round as a home office or hobby room.

The Xtend 4.0+ uses structural insulated panels throughout walls, floor and roof. Each 97mm wall SIP consists of 75mm polystyrene insulation between two OSB sheets. With 15mm tongue and groove external cladding, 28mm wall battens and internal MDF lining, total wall thickness reaches 177mm. The 108mm SIP floor and 122mm SIP roof extend insulation across the whole envelope. The 1.2mm EPDM rubber roof membrane is UV-stabilised and rated for 50 years. All glazing is 28mm A-rated double glazed safety glass in UPVC 5-chamber frames. The result is an energy rating of 78 (category C).

Structure: SIP panels with 75mm polystyrene core between OSB sheets. External cladding: 15mm kiln-dried tongue and groove timber. Internal lining: pre-primed MDF with vertical beaded profile. Floor: 108mm SIP panels, unfinished. Roof: 122mm SIP panels 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 base is required before delivery or installation. A concrete slab or equivalent hard standing is recommended. No base is supplied. The buyer is responsible for preparing the ground. The floor panels are SIP construction and are supplied no additional flooring is included.

The Xtend 4.0+ arrives as pre-cut modular SIP panels ready for assembly. A step-by-step installation guide is included along with all fixtures, fittings and exterior fascias. The modular design makes the build straightforward. Forest also offer a professional installation service if you prefer not to self-build. No specific assembly time or crew size is stated by the manufacturer.

Forest offer a professional installation service carried out by expert fitters. You must have a solid level base ready before the installation date. Installation does not cover electrics, base preparation or other accessories. Contact Forest for scheduling details after purchase.

Forest do not install electrics. The building is designed for it though 28mm wall battens and 45mm roof battens create cavities for routing cables and recessing lights. All electrical work must be carried out by a qualified electrician. No wiring is supplied.

Treat the exterior timber cladding on assembly and every year after using a product such as Sikkens Cetol HLS Plus or Osmo Natural Oil Wood Stain. The EPDM roof is maintenance free. Clean glazing as needed. Annual treatment is required to maintain the 15-year structural guarantee.

The internal floor space of 3.67m x 2.68m gives you just under 10 square metres. That comfortably fits two desks for a dual home office setup or one large desk with storage units. There is room for a small sofa or a compact gym setup with a bench and weights. It works well as a music room, art studio or hobby space. The full insulation and double glazing make it practical for daily use throughout the year not just in summer.

Most garden offices fall under permitted development rules in England if they are single storey and used for domestic purposes. This model has a 2500mm ridge height and 2400mm eaves height. These figures typically sit within permitted development limits but rules vary by location. Always check with your local planning authority before you build. This is not legal advice.