premium range

Detailed Specification

Please note: all imperial measurements are approximate and the Forest Xtend Insulated Garden Office is made from metric measurements. We would recommend that the base is at least 200mm bigger in each direction.

Product Name: 13 x 11 (4.05m x 3.42m) Forest Xtend 4.0+ Insulated Garden Office with Double Doors
Footprint (Front Width): Including Roof Overhang: 4.05m (13'3")
Excluding Roof Overhang: 4.03m (13'2")
Internal: 3.67 (12'0")
Footprint (Depth): Including Roof Overhang: 3.42m (11'3")
Excluding Roof Overhang: 3.04m (9'11")
Internal: 2.68 (8'9")
Height to Ridge: External: 2.50m (8'2")
Internal: 2.06 (6'10")
Height to Eaves: 2.40m (7'10")
Walls: Total wall thickness (including SIP Panels, internal and external cladding and cavities) = 177mm
Internal: 97mm thick insulated walls consists of 75mm of polystyrene insulation sandwiched by two sheets of Oriented Strand Board (OSB)
External: 15mm thick premium interlocking tongue and groove boards mounted to framing battens
Framing: Wall Framing: 28mm
Roof Battens: 45mm
Door: Double uPVC reinforced 5 Chamber
Door Opening (Height x Width): 1.95m x 1.60m (6'5" x 5'3")
Door Lock: 7 point multi-Lock with ultion three star security barrel
Roof Type: Pent
Roof Material (External): 1.2mm EPDM black rubber roof
Roof Material (Internal): Total roof thickness = 122mm
11mm OSB + 100mm insulation + 11mm OSB
Roof Life: EPDM 50 Year roof life expectancy
Floor Material: SIP Panels - Total floor thickness = 108mm
Boarded, Oriented Strand Board (OSB) and tongue and groove
Floor Joists: 70mm x 45mm Wrapped in a damp proof membrane
Floor Joists Direction: Front to back
Window(s): Front Width: 1 x full-length window uPVC 5 chamber with 1/2 opening
Depth: 1 x uPVC 5 chamber full-length side window with 1/2 opening
Window / Wall Panels: Not interchangeable
Window Glazing Material: 28mm double glazing safety glass with energy rating A
Windowless Option Available: N/A
Energy Rating for Building: Energy efficiency model rating of 78 (category C)* with potential to increase to 82 (category B) with the addition of a photovoltaic solar panel
Treatment: None - kiln dried
Recommended Treatment: External: Sikken Cetol HLS Plus, Restol Wood Oil, Timmersol ETS Double Protectant, Osmo Country Colour, Osmo Natural Oil Woodstain
Internal: Protek Royal Range (please click here)
Portabase Available: N/A
Manufacturer's Guarantee: Underwritten with a 15 year structural guarantee
FSC Certified Timber: N/A
Free Delivery: Yes*
Other Sizes Available: Front Width x Depth:
2.54m x 2.90m - 2 long windows with one 1/4 opening
2.54m+ x 2.90m - 2 long windows with one 1/2 opening
2.98m x 2.90m - 3 long windows with one with a 1/4 opening
2.98m+ x 2.90m - 3 long windows with two1/2 opening
4.05m x 3.42m - 3 long windows with one 1/4 opening
4.05+m x 3.42m -2 long windows with two 1/2 opening
Assembly Available: Optional
EAN Number: 5013053183632 and 5013053183656
Weight: 2400kg
Manufacturer: Forest Garden Ltd
Country of Origin: United Kingdom


* Based on lighting from 3 x 4 watt LED bulbs and heat from a high efficiency wall mounted heat pump


Forest Xtend 4.0+ Insulated Garden Office

As more and more of us are working from home, the need for a quiet, dedicated home office is becoming urgent for people all over the UK. You can achieve the perfect work/life balance by opting for a garden home office. The Xtend 4.0+ from Forest offers just about everything you could need in a home office. It boasts a clean, contemporary look, it stays cool in the summer and warm in the winter, it is surprisingly easy to build and, most importantly, it costs a fraction of the price of a traditional home extension. With an opening side window as part of the package too (you'd be surprised how many similar products don't include one!) regulating the internal temperature and airflow is a breeze. Available in a range of sizes, there is certain to be an Xtend to suit your needs.

As if that wasn't enough, Forest can deliver the Xtend within 3-4 weeks of you placing an order, so you can be up and running in your new home office in next to no time! If you have a little more time to work with, the delivery time increases only to 5-6 weeks if you want to take advantage of Forest's professional assembly service. By choosing assembly, you can sit back, relax, and have your new workspace built for you. If you can find someone to build a conventional extension on your home within 6 weeks at the same price or better than the Xtend, we suggest you take them up on the offer! Please be aware, however, that these timescales may be extended during peak times of the year or due to unforeseen circumstances.

Why Buy an Xtend?

If you have found yourself trying to work in a cramped spare bedroom while the sound of the washing machine provides a constant distraction, or perhaps you have had one instance too many of the family pet or one of your children making a surprise appearance in a video meeting, the Xtend could be precisely what you need to ensure distractions are a thing of the past. Not to mention, having a garden home office would mean no more commuting, more time spent at home with loved ones, and more space freed up in your house for other uses. Plus, with a 15-year structural guarantee, you can rely on your new home office to provide valuable working space for many years to come. Join the revolution today and see exactly why more and more people are choosing to have an office in their garden!

Don’t have a desk job or can’t work from home? No problem! The Insulated Garden Office could provide you with the perfect space to set up for a variety of different business types, or could just as easily be used as somewhere to spend your leisure time. We regularly see garden buildings such as the Xtend used by beauticians, nail technicians, dog groomers, massage therapists, personal trainers, and more! And of course, the Xtend is not just a building perfectly suited to work use. It could be just the space you need to set up an art studio, a music room, a fitness suite or even simply a quiet spot for rest and relaxation in the tranquil setting of your garden. The possibilities are almost limitless, but you may take extra inspiration from checking out our product images, showing some of the great ways you can take advantage of the Xtend.

See our key features tab for more information about the Xtend’s quality components.

About Forest

Forest Garden Ltd is the UK's leading manufacturer and distributor of timber garden products. They are proud to be a British company using sustainable, British timber. The majority of the timber they use is grown and felled from managed UK forests across Scotland. After felling, the timber is cut and processed in a nearby sawmill and taken to their manufacturing operation in rural Worcestershire. At their manufacturing site, they are always investing in technology to ensure product consistency and quality. It is there that they produce the widest range of garden buildings, fencing and structures available in the UK. Many of Forest’s products come with high specification features at no extra cost, and they also offer free delivery and pick your own delivery dates to the vast majority of mainland UK addresses. This cements their reputation as the “go-to” choice for thousands of customers looking to enhance their gardens every year.

Key Features

Structural Insulated Panels (SIPs)
  • The core structure of an Xtend building is made from SIPs panels - a high performance material for building construction. The 21st century way to build
  • 7mm thick insulated walls consist of 75mm of polystyrene insulation sandwiched between two sheets of oriented strand board (OSB)
  • Gives structure and insulation in one pre-assembled and cut-to-size panel
  • Total wall thickness, including SIPS panels, internal and external cladding and cavities, is 177mm
  • Roof is 11mm OSB + 100mm insulation + 11mm OSB = 122mm total
  • This all comes together to make for a snug interior during the colder months, but also one that remains cool during the summer
External Cladding 
  • Pre-cut external timber cladding panels for quick and easy assembly; many modern homes are now built in this way, so why not your home office?
  • No measuring and cutting every single batten and board to size before mounting
  • Cladding panels are simply positioned on the building and screwed into place
  • Panels are made with 15mm thick premium interlocking tongue and groove boards mounted to framing battens
  • Comes untreated, so you must apply a suitable timber treatment of your choice. The manufacturer recommends: Sikkens Cetol HLS Plus; Restol Wood Oil; Timmersol ETS Double Protectant; Osmo Country Colour; Osmo Natural Oil Woodstain
Internal Cladding
  • Pre-cut interior MDF panels for quick and easy assembly of walls and ceiling
  • No measuring and cutting every panel
  • Wall panels are mounted to 28mm thick battens creating a cavity perfect for routing electrical wiring (we recommend you consult a trained electrician when installing electrics)
  • Roof battens are 45mm thick to allow for recess roof lights
  • Comes with primer applied – can be painted in a colour of your choice using standard interior emulsion paint
  • The panel design has a vertical beaded profile
  • The floor is left unfinished for you to add your own choice of covering
  • Includes damp proof membranes
Roof Covering 
  • External roof covering is made from 1.2mm thick EPDM black rubber
  • It creates a maintenance free waterproof membrane
  • Does not crack, split or rot
  • Does not support moss or algae growth
  • UV stable & environmentally friendly
  • Safe and easy to install – the system is laid with cold applied adhesives (supplied)
  • One piece sheet means no joints and no leaks
  • 50 years roof life expectancy
  • Anthracite grey fascias included
  • Cladding on under-hangs
Windows & Doors
  • Window material: uPVC 5 chamber
  • Window colour: Anthracite grey externally with grained finish smooth white internally
  • Window locking: Two double clasp, mushroom headed espagnolettes
  • Door material: uPVC reinforced 5 chamber
  • Door colour: Anthracite grey externally with grained finish, smooth white internally
  • Door locking: 7-point multi-lock with ultion three-star security barrel, providing peace of mind when leaving valuables inside
  • Glazing 28mm, A-rated, double glazed, safety glass
  • Opening side window allows you to regulate the internal temperature and airflow with ease
Energy Efficiency
  • Highly efficient due to insulated walls, roof, and floor
  • Double glazed windows
  • Warm in Winter, cool in Summer
  • Energy efficiency model rating of 78 (category C)*
  • Potential to increase to 82 (category B) with the addition of a photovoltaic solar panel
  • *Based on lighting from 3 x 4 watt LED bulbs and heat from a high efficiency wall mounted heat pump
Why Choose the Forest Xtend?
  • Can be delivered within 3-4 weeks, one of the fastest (if not the fastest) timescales for any similar products on the market; please be aware that this may be extended during peak times
  • Not all our competitors offer installation; so, if you want to avoid the hassle of ringing around for quotes, or indeed having to spend your valuable time building it yourself, Forest offer optional assembly for a great price
  • Xtend has a market-leading and verified energy efficiency rating
  • Walls are as much as 47% thicker than similar products on the market
  • Roof up to 30% thicker than competitors
  • Under-hangs feature cladding for a superior look and less maintenance; many competitor products do not, leaving buildings looking unfinished
  • The Xtend features damp proof membranes
  • A floor that is as much as 400% thicker and better insulated than some other leading products
  • Easier to build thanks to its state-of-the-art design
  • Free delivery to Mainland UK with almost no exceptions; some competitors charge as much as £600 for delivery to certain areas
  • Some similar products don’t include a side window, and if they do, it isn't always an opening window
  • A comprehensive 15-year warranty, whereas most competitors only offer a 10-year guarantee
  • Primer pre-applied to interior walls, meaning you can paint straight onto them with interior paint
  • Xtend has hidden nail panels for a sleek, professional finish
  • Hard-to-beat pricing when compared to competitors, especially for such a high-quality product


Important Information:   Timescales are indicated on this page.  Lead times are counted in working days (Monday – Friday) excluding Bank Holidays. You will be contacted towards the end of your timescale by either Forest's Delivery Team or Forest's preferred carrier.  Neither elbec nor Forest will be able to supply any further information on your delivery date during this timescale.

ALL DELIVERIES ARE DELIVERED TO KERBSIDE OR DRIVEWAY. All of the Forest products are delivered flat packed, (other than fence panels which are delivered fully constructed) direct to your home, and are supplied with a set of instructions to support assembly.

If you have ordered more than one item, they may arrive at different times.

Booking Delivery

You will be contacted towards the end of your timescale by Forest/their Courier with a delivery date. If this date is not convenient you can reply to the message to book a more convenient delivery date. The delivery timescales are as stated on the product page.

The delivery timescales to these areas may be extended.
AB1, AB10,-AB16, AB21-AB25,AB30-AB39, AB41-AB45, AB51-AB56, CA1-CA28, CO1-CO16, DD1-DD10, DG1-DG14, DG16. DH1-DH9, DL1-DL17, DT3-DT7, EH1-EH2,EH10-EH1-EH49,EH51-EH55, EX1-EX24,EX31-EX38, FK1-FK21, G1-G5,G11-G15,G20-G23,G31-G34,G40-G46, G51-G53,G60-G69,G71-G78,G81-G84, IP1-IP33, IV1-IV28,IV30-IV32,IV36,IV40,IV54,IV63, KA1-KA30, KW1-KW14, KY1-KY16, ML1-ML12, NE1-NE1-NE49,NE61-NE70, NR1-NR35, PA1-PA38, PE30-PE37, PH1-PH26, PH30-PH41,PH49-PH-PH50, PL1-PL35, SR1-SR8, TA20, TA22, TD1-TD15, TQ1-TQ14, TR1-TR20,TR26-TR27, AND TS1-TS29.

We are sorry but Forest do not deliver or offer an assembly service to the following Postal Codes:
BT1-BT99, GY1-GY9, HS1-HS9, IM1-IM9, IV41-IV56, JE1-JE5, KA27-KA28, KW15-KW17, PO30-PO41, PO49, TR21-TR25.

Prior to Delivery

Once you have a confirmed delivery date if you provide us with a mobile number, we can confirm the day before delivery if your delivery will be morning or afternoon.

Upon Delivery

Your order will be delivered kerbside or on your driveway. Due to health and safety, and insurance liabilities, the driver will not be able to take your goods to the back of your property but – upon request – may place the product at the side of the house if there are no access issues. This is to avoid risking damage to your property while delivering to an unsafe location. We will not be able to go through your property.

We recommend against arranging for a third party to install the product before its delivery and checking that all parts are present, and we cannot be held liable for any third-party costs caused by delays


This option will extend the leadtime by up to 3-4 weeks.

If you have selected the installation option the product and installation of your product may be on different days. Once you have been given a delivery date by Forest's delivery team you will then be contacted by their installation team to confirm your installation date and the process. The installation team will require a minimum of 2' clearance all the way around your building and the installation team will not be able to enter through your property.

13 x 11 (4.05m x 3.42m) Forest Xtend 4.0+ Insulated Garden Office with Double Door

from £11,499.99
NEW - Sale
NEW - Guarantee - 15 year - gold
NEW - Installation - Express Installation
NEW - Interest Free Credit

Product code - 90040037


Description Information

The Forest Xtend 4.0+ Insulated Garden Office with double doors and 2 fixed long windows which includes a 1/2 opening side window on the front and side elevation, provides the perfect workspace solution for anyone who works from home. Away from the distractions of your home, it provides a quiet environment that is perfect for concentrating on your work. Say goodbye to being cramped into a small spare bedroom or getting back ache from trying to work in your bed! Just some of the key features of this superb building include:

  • Highly energy efficient, and remains warm in the winter while cool in the summer; read more below for extra detail about how this is achieved
  • Comes with a 15-year structural guarantee, so it can be relied upon to provide many years of service
  • A much cheaper alternative to a traditional extension and is delivered free to most UK mainland addresses
  • State-of-the-art manufacturing techniques ensure a building that is surprisingly straightforward to assemble

View full specification Delivery

Usually delivered: 30-35 Working Days.

Note: Currently not available for delivery to Offshore Post Codes.

excludes installation option
Choose your product

Your choices:

  • 13 x 11 (4.05m x 3.42m) Forest Xtend 4.0+ Insulated Garden Office with Double Door£11,499.99