Forest Xtend 4.0+ Insulated Garden Office 4.05m x 3.42m (97mm)

Product Code: BFD25575
EXTRA 5% Off All Forest Orders over £350 Ending in
Enter Voucher Code FOREST5 at Checkout
Buy Now! Extra 10% off ALL Wooden Garden Buildings over £699 Ending in
Simply Use Voucher Code TIMBER10 at Checkout
  • DESIGN: The future of garden offices, the Xtend range uses cutting-edge Structural Insulated Panels (SIPs) resulting in the best insulated garden rooms offering true year-round comfort
  • CONSTRUCTION: Fully insulated 97mm thick SIP walls; handsome 15mm tongue and groove exterior cladding; and pre-primed interior cladding for an impressive 177mm thickness overall
  • ROOF AND FLOOR: 122mm SIP roof completed with interior cladding and fully insulated 108mm SIP floor on protected bearers (images shown with laminate flooring added)
  • GLAZING: A-rated double glazing throughout including glazed double doors and 2 full length windows (top half of windows open)
  • INCLUDED: Maintenance free EPDM roof covering with 50yr life expectancy
  • GUARANTEE: 15 year structural guarantee
  • Other sizes available here

Please ensure a solid, level base is constructed BEFORE your installation date. Installation does not include electrics or other accessories. Please see the installation section below for more details.

  • Accessories
  • +
    £1,369.00 £1,669.00
    Hubi Solar Power Station Premium 750

    Hubi Solar Power Station Premium 750 - £1369

    Enjoy free electricity while reducing your carbon footprint with the Hubi Solar Power Station Premium 750 - the intelligent way to achieve energy self-sufficiency when powering a holiday cottage, construction site office or any garden building.

    You can have this all-in-one solar power hub up and running in minutes, thanks to simple plug and play technology, which means that no mains connection is required. Part of the next generation of solar stations, the kit includes a super-sized solar panel with frame and stand, a solar power station with dashboard, and built-in battery storage.

    Use the mounting stand to peg the extra-large solar panel to soft ground or, alternatively, position it on a roof - the choice is yours. Either way, it is exceptionally efficient and can charge a flat solar battery to full capacity in as little as 5 hours.

    Smart, contemporary and exceptionally easy to manoeuvre, the solar power station, itself, comes in bespoke, white casing and features a clear, user-friendly dashboard.

    This includes a 12v auto socket, 5v USB charging, solar lighting ports and a 3-pin mains socket, which is suitable to power any 230AC appliance up to 300w, so your television, laptop and solar garden lighting are all perfectly compatible.

    Thanks to built-in battery storage, any electricity generated can be stored for later use, so there's nothing to stop you from powering your garden building, independently of the National Grid, at any time of the day or night.

    This state-of-the-art solar station can deliver 750Wh of energy over a 24-hour period, and even more during the summer months. It is fully CE-approved, RoHS-compliant and supplied with a 2-year guarantee for your added peace of mind.

    If you're not practically minded and concerned about installing this solar power kit, there's no need to worry because absolutely no electrical skills are required. The equipment arrives fully assembled and ready to go - simply plug, play and enjoy electricity in your garden building.

    This mobile energy system comes in 3 specific sizes, which deliver 250Wh, 500Wh or 750Wh of energy per day respectively. You should choose the Hubi Solar Power Station Premium 750 if you need to run multiple devices in a holiday cottage, construction site office or any garden building.

    If lighting is a requirement, we sell 3 dedicated solar light packs too, all of which are compatible with any of the 3 premium solar power stations.

    Free delivery is available to most UK addresses.

    • Enjoy free electricity, while lowering your carbon footprint
    • This solar station delivers 750Wh of energy per day
    • Super-sized solar panel features sturdy frame and mounting stand
    • Charges a flat solar battery to full capacity in as little as 5 hours
    • Solar power station features bespoke, white casing and a user-friendly dashboard
    • Dashboard includes 12v auto socket, 5v USB charging, light ports and 3-pin mains socket
    • Comes with built-in battery storage
    • Fully CE-approved and RoHS-compliant
    • Reassuring 2-year guarantee
    • 250Wh, 500Wh and 750Wh solar power stations available
    • Choose the 750 solar station to run multiple devices in a holiday cottage, construction site office or garden building
    • 3 dedicated solar lighting packs available too
    • Solar power stations and solar lighting are not included within our garden building installation service
    • Free delivery to most UK addresses
Spend over £99 to qualify for PayPal CreditSpend over £99 to qualify for PayPal Credit

Spend over £99 to qualify for PayPal Credit

Tick In stock



Forest Xtend 4.0+ Insulated Garden Office 4.05m x 3.42m (97mm) Technical Drawing
Brand Forest Xtend
Cladding Tongue and Groove
Construction Type SIPs panels with external Tongue & Groove cladding/internal MDF cladding
Door Type Double Doors
Eaves Height 2400
Size 13' x 11'
Internal Depth 2680
Internal Width 3670
Opening Windows 2 windows
Ridge Height 2500
Roof Covering EPDM Rubber Membrane
Roof Style Pent
Material Wooden
Guarantee 15 years
Depth at Base 3040
Depth including Overhang 3420
Width at Base 4030
Width including Overhang 4050
Door Height 1950
Door Width 1600
Glazing Material Double Glazing
Locking System 7 Point Multi-Lock With Ultion Three Star Security Barrel
Floor Material Structural Insulated Panels (SIPs)
Floor Thickness 108
Roof Material Structural Insulated Panels (SIPs)
Roof Thickness 122


Introducing the Xtend 4.0+, one of Forest Garden's range of premium garden offices. Designed to meet the needs of the growing number of people working from home, the Xtend Garden Office allows you to create a healthy separation of your work and home life - all in your own garden. Fully versatile, this 106sqft year-round garden room is also perfect as your garden gym, family living space or hobby studio.

Cutting Edge Construction

With over 50 years of expert experience as one of the UK's largest manufacturers of timber garden buildings, it is no surprise that Forest Garden are leading the way in innovative construction. The Xtend range is designed with Structural Insulated Panels (SIPs) at its core. SIPS are a high-performance, energy-efficient building material used in some of the best new homes being built in the 21st century. By using this revolutionary material when building the Xtend garden rooms, Forest have ensured that you'll have a work place that is damp-free, cool in summer, and warm in winter. Plus, unlike most other brands of garden building that only insulate their walls, the Xtend Garden Offices utilise SIPS for the walls, roof and floor for an energy efficient, full insulated build that you will enjoy throughout the year.

The Walls

The wall SIPs each consist of 75mm of insulation sandwiched between two sheets of oriented strand board (OSB) for a remarkable 97mm thickness. These are preassembled and already cut to size for easy construction. External and internal cladding is then added to each wall SIP.

The external cladding is 15mm premium tongue and groove made from kiln dried timber and supported by 28x28mm framing. The interlocking structure of tongue and groove offers superior weather protection as well as a modern finish.

The internal cladding is pre-cut MDF with an attractive vertical beaded profile. Conveniently already coated in primer, once assembled, the interior walls are ready for you to paint in your choice of colour. Standard interior emulsion paint is all you need.

With the impressive combination of SIPs, exterior cladding, interior cladding and the cavities in between, the resulting thickness is a mighty 177mm.

Floor and Roof

Surpassing most brands who will only insulate the walls, Forest have used the innovative SIPS for the walls, floor and roof. The floor SIP has a total thickness of 108mm so not only is it another source of insulation but it is strong enough to withstand years of footfall. Plus, the floor is supported by wrapped floor bearers to prevent rot and damp rising from the ground. Inside, the floor is left uncovered for you to add your choice of flooring, such as carpet or laminate.

The roof SIP has even thicker insulation and is also sandwiched between two boards of OSB for a total 122mm thickness. This offers robust protection against the elements. Plus, the roof features the same primed MDF interior cladding as the walls for an attractive finish.

The roof surface is finished with EPDM which is a rubber membrane roof covering far superior to felt. With an incredible 50 year guarantee, the EPDM will not crack, split or rot and is resistant to moss or algae growth. It is UV stable so won't fade or deteriorate after long exposure to sunlight. The maintenance-free membrane is applied as one sheet so there are no joins to worry about. The roof is then finished off with modern anthracite grey fascias to complete the handsome appearance of this modern garden room.

Doors and Windows

Offering ample light, the Xtend 4.0+ features fully glazed double doors with a full-length adjacent window pane which contains a half-height opening window. To the side of the office is a further full-length pane with another half-height opening window.

The doors and windows all boast a uPVC 5 chamber specification. Modern anthracite grey with a grained finish on the exterior, the door and window frames are smooth white on the interior to suit your chosen decor.

All glazing is A-rated, double glazing for improved heat and noise insulation. The glass is toughened for safety. A discrete window vent supports the pleasant working environment.

The door frame is reinforced. Security is provided by a key-operated 7-point multi-lock with a Ultion three-star security barrel. The opening windows are also lockable with their own keys.

Also take a look at the Xtend 2.5 and Xtend 3.0 for different sizes and different window and door configurations.

Energy Efficiency

Because the SIPs are pre-insulated, you can rest assured that your new outdoor office will be warm in winter and cool in summer. The A rated, double glazed windows support this insulation. In fact, all the insulated garden rooms in the Xtend range are certified as having an energy efficiency of category C with the potential to increase to B with the addition of a photovoltaic solar panel.

With the combination of the SIPs, external cladding, internal cladding and cavities, the total thickness of the wall panels is a mighty 177mm. This far exceeds standard log cabins and makes the Xtend ideal for comfortable year-round use as a garden office or family space.

Installation and Maintenance

The ready-made SIPs and pre-cut cladding are designed to make building the garden home office as easy as possible. However, if you are not confident with DIY or simply limited by time, Forest Garden offer an installation service. Their dedicated fitters will provide a quick, professional construction using their expert knowledge and skills.

The timber is supplied untreated and will need to be treated upon assembly and annually thereafter. Forest Garden recommend the following products for use with their kiln-dried timber: Sikkens Cetol HLS Plus, Restol Wood Oil, Timmersol ETS Double Protectant, Osmo Country Colour and Osmo Natural Oil Woodstain.

The garden office comes with a 15 year structural guarantee from Forest Garden.

Adding Electrics

Though we do not provide an electrician service, the battens on the interior cladding are designed to leave ample room for wiring and/or recessed ceiling lights should you wish to add mains electrics later.

We do offer a range of solar power options for powering and lighting your garden office.


Delivery of the garden office is free to most UK postcodes. Some remote postcodes may incur a surcharge. Details of this will be available via the postcode checker and at checkout.

Many of Forest Garden's garden buildings are available with a free pick-a-day delivery option allowing you to choose the most convenient delivery date. If this is available for this product, you will see the Pick-a-Day icon at the top of the page.

If you have any further questions, our UK-based, knowledgeable customer service team will be happy to help you. You can call our team directly or use the live chat option at the bottom of the screen.

Quick Overview

  • 106 square feet of multi-purpose living space
  • Built with cutting-edge Structural Insulated Panels for year-round comfort
  • Internal cladding with vertical beaded profile primed for you to paint your choice of colour
  • External cladding made with 15mm tongue and groove, kiln-dried timber
  • Wall SIPS, plus internal cladding, plus external cladding plus cavity space creates a mighty 177mm thickness
  • Roof SIPs are 122mm thick in total
  • Floor SIP is 108mm thick and left uncovered for you to complete with your own carpet, laminate, etc
  • EDPM rubber, maintenance-free, 50yr life expectancy roof covering
  • Anthracite grey fascias
  • Fully glazed double doors and a full-length adjacent window pane with half-height opening section
  • Further full-length pane to the side with another half-height opening window
  • Doors are uPVC reinforced 5-chamber with 7-point locking mechanism
  • Windows are uPVC 5-chamber
  • Opening windows are key-lock operated
  • Double glazing throughout - A rated
  • Energy efficiency rated C
  • Installation service available
  • Other sizes available
  • Free delivery to most UK postcodes

Why choose an Xtend 4.0+ Garden Building?

Achieve your ideal work/life balance with the Xtend range of garden buildings from Forest Garden. These new buildings have everything you could wish for in a home office: contemporary looks, real energy efficiency, ease of construction and keen pricing. All brought to you by the UK’s largest manufacturer of timber garden products.


Pre-cut external timber cladding panels for quick and easy assembly. Panels are made with 15mm premium interlocking tongue and groove boards mounted to framing battens. Comes untreated so we recommend the application of any of the following: Sikkens Cetol HLS Plus, Restol Wood Oil, Timmersol ETS Double Protectant, Osmo Country Colour and Osmo Natural Oil Woodstain.


The core structure of an Xtend building is made from SIPs – a high performance material for 21st century building construction. The SIPs are 97mm insulated walls consisting of 75mm of polystyrene insulation sandwiched by two sheets of oriented strand board (OSB). Total wall thickness including SIPS, internal and external cladding, and cavities is an impressive 177mm.


Interior MDF panels for walls and ceiling, pre-cut for quick and easy assembly. Wall panels are mounted to 28mm thick battens creating a cavity perfect for routing electrical wiring. Comes with primer applied, ready for you to paint in a colour of your choice using standard interior emulsion paint. The floor is left unfinished for you to add your own choice of covering.


External roof covering is made from 1.2mm thick EPDM black rubber. It creates a maintenance free, waterproof membrane. With 50 years life expectancy, it will not crack, split, fade or rot. Anthracite grey fascias provide a stylish finish to the contemporary roof.


Windows material: uPVC 5 chamber. Door material: uPVC reinforced 5 chambers. 28mm, A-rated, double glazed, safety glass throughout. The window and door frames are anthracite grey with a grained finish externally and white with a smooth finish internally. All doors and opening windows are fitted with key operated locks.


Highly efficient insulated walls, roof and floor, plus double glazing for a year-round garden room that is warm in winter and cool in summer. Energy efficiency rating of 78 (category C) - based on lighting from 3 x 4-watt LED bulbs and heat from a high efficiency wall mounted heat pump. Potential to increase to 82 (category B) with the addition of a photovoltaic solar panel.




A perfect fit for traditional or modern gardens.



Although we do not install electrics as part of our installation service, the Xtend range has been designed for routing electrical wiring and recess roof lights!


250 (H) X 405 (W) X 342 (D)CM






Space is at a premium in most homes and extensions are costly. An Xtend garden building is constructed from high quality, energy efficient materials and is underwritten with a 15 year structural guarantee. You can be confident with Xtend that quality has not been compromised over price.



Xtend is a clever choice for your garden building as it comes delivered in pre-cut modular SIP panels ready for assembly. Some of the best designed new homes are now made this way, so why not your new garden building? A step-by-step guide means the build is incredibly straightforward.


Xtend garden buildings are not just brilliant spaces for working at home. More than just a home office, Xtend opens up affordable space for countless uses such as hobbies, exercising, entertainment and accommodation. With Xtend, size and versatility can be combined perfectly to suit your requirement for extra space. Make your space your own.



Keeping you warm in winter and cool in summer, Xtend delivers real energy efficiency. Double glazed windows, highly efficient insulated walls, roof and floor combine to drive down energy costs. It’s a fact that Xtend garden buildings have a higher EPC rating than the average home.



It only takes a glance to see that an Xtend garden office has the pleasing lines and contemporary design to catch the most discerning eye. Xtend is at home in any garden, be it traditional or modern - just how great design is meant to be.



Everything you need to know about Xtend by Forest Garden

Xtend By Forest - How to Build


Trustpilot Reviews

Xtend 4.0+ Features

From The Supplier: Forest Garden


"We're proud to be the largest and most trusted manufacturer and distributor of garden timber products in the UK" - Forest Garden

Making British Gardens Great


At Forest, we know a fair bit about fences. And sheds for that matter. In fact, we've been one of the UK's most trusted manufacturer and distributor of quality wooden garden products for over 50 years.


With two sawmills in the UK processing locally-sourced timber, and a Head Office in Hartlebury, Worcestershire, you’ll find our range of garden buildings, fencing, decking and decorative structures for sale across many sites online and in over 3,000 retail stores. From the forest to the doorstep, we are involved every step of the way to ensure we bring you the best product and service.


Well made in Britain


The majority of the timber we use is grown and felled from managed UK forests across Scotland and Wales. After felling, the timber is cut and processed in one of our nearby sawmills and taken to our manufacturing operation in the heart of Britain. It is here our skilled workforce proudly produce the widest range of garden buildings, fencing and structures available in the UK.


All of the products that we sell are dispatched from this site. The final part of their journey is managed by our dedicated delivery department who are responsible for distribution direct to customers' homes by our fleet of vehicles.


Home Grown


We're proud to say that the majority of the timber we use is cut in our very own sawmill from trees grown in the UK.


Not only that, but our range is certified by the Forest Stewardship Council and the majority of our products carry the FSC logo - so you know that our timber is ethically sourced from well-managed, sustainable forests that are replanted for future generations.


(Certification number TT-COC-001790, Issue date 5 March 2015)


Helping Everyone Thrive


We like to do our bit for charity and are proud to support Thrive. Thrive uses gardening as therapy to bring about positive changes in the lives of people living with disabilities or ill health, or those who are isolated, disadvantaged or vulnerable.





"We are excited and proud to be a carbon neutral business. We work with Carbon Neutral Britain, the UK’s leading offsetting initiative provider to offset our environmental impact."

- Forest Garden

We Are Now Carbon Neutral!


We believe that a successful business is also a responsible business. This includes being dedicated to playing our part in protecting the environment, supporting our community and making sustainable choices. It also means that we value our colleagues and their welfare, putting policies into practice to make sure we are an employer of choice in our field. For us, this is a passionate commitment that runs through everything we do.


All of us who work with Forest Garden can be proud of what we do and this is embodied in the 3 fundamental principles - Keeping It GreenSupporting Our Colleagues and Supporting Our Community.

Xtend Garden Buildings Installation


Forest Xtend Garden Buildings Installation

Forest Garden provide their own expert fitters to install your Xtend Garden Building. With dedicated experience installing Forest's Xtend Range, they will provide a professional service that is second to none. They aim to carry out installation within 1 - 5 working days of the delivery of the garden office and it is usually quicker than this estimate.


After your order, Forest Garden will send you a detailed document covering the requirements of a suitable base for a Xtend Garden Building.


Forest Garden do not provide a service for the preparation of the base area or for installation of electrics, wi-fi, solar lighting or plastic bases. If you require assistance with these, we recommend the use of for locating a reputable tradesperson in your area.


If you choose to install the garden office yourself, you can use the detailed guide which includes step by step images to help you. Forest Garden also have a Technical Helpline if you have any questions along the way.


If you are using an independent tradesperson to install your garden building, please allow enough time for the garden building to be delivered and the parts inspected before booking your tradesperson.


Please inform customer service BEFORE you order, if you believe there are restrictions which could impact the delivery and installation of the garden room.


Xtend DeliveryXtend Delivery
Delivery VanDelivery Van


We offer FREE Delivery to the majority of mainland postcodes but some areas may incur an additional carriage charge (see below). Please use our postcode checker further up the page (below the add to basket button) or within checkout to check delivery is available to your area.

£49.99 - BH, BN, CA, CT, DH, DL, DT, EX, IP, LA, LL, ME, NE, NR, PL, PO, SA, SO, SR, TA, TN, TQ, TS

£119.99 - DD, DG, EH, FK, G, IV, KA, KY, ML, PA, PH, TD. Please allow an additional 5-10 working days for delivery into these postcode areas.

£124.99 - AB


Your delivery will be made between 8am and 6pm on your pre arranged delivery date; our delivery team will contact you to book via phone.

Our service is a Kerb side pallet drop delivery by a crane off-load vehicle. Unfortunately we will not be able to unpack your Xtend Garden Building and take your goods to the back of the property. We typically plan to deliver to the front garden or drive.

Xtend Garden Buildings are delivered in two packages, flat packed, direct to your home and supplied with a comprehensive set of instructions to help you get started.

Please Note - delivery is NOT available to the following postcode locations: BT, GY, HS, IM, IV1-11,14-28,40-63, JE, KA26-28, KW, PA20,28-31,34, PH32-35,41, PO31-41, TR 

This example represents the typical costs of using PayPal Credit as a standard funding method. Interest on your instalment offer is fixed for it's duration. See terms for more details.
Representative Example
  • Purchase Rate 23.9% p.a. (variable)
  • Representative 23.9% APR (variable)
  • Assumed Credit Limit £1200