Installed Garden Room, Large Sizes, Basebox by Green Retreats (up to 28m²)
Item #BaseboxGardenRoomLarge
- Premium Garden Rooms: 20m² – 28m²
- Built for Longevity: 30-year design life supported by a 12-year structural guarantee
- Total Insulation: Year-round comfort via eco-friendly floor, wall, and roof insulation with premium double glazing.
- Hassle-Free Install: Professional completion in 1–2 days; typically requires no planning permission
- High-Spec Features: Secure uPVC French or sliding doors and a maintenance-free, soft-sheen white interior
- Exterior Finish: Eco-friendly exterior cladding (requires painting within 6 months)
The price includes free delivery in Band 1. Extra charges apply outside of this area. Please refer to the map under Delivery & Returns for more information.
To enquire about this item, please email costco@greenretreats.co.uk or call 01296 328260.
Costco’s customer satisfaction guarantee and returns policy does not apply to special order merchandise, custom merchandise and installed merchandise. However, your legal rights are unaffected. For further details, please see Delivery & Returns
The Basebox large range is an affordable, compact and fully insulated garden room available in sizes from 13 sizes from 20m² to 28m², professionally installed to create practical year-round space for use as a large garden office, fully equipped home gym or a family space. The Basebox design is scaled back and simplified to keep this building our best value in the range. The Basebox building requires painting in your chosen colour of outdoor sealing paint within 6 months of purchase, making this design a fun and stylish addition to your garden. If you’re looking for a zero-maintenance option with natural wood effect cladding, or a building with additional styling features, please see the Basebox Plus listings).
Installed by Green Retreats, the UK’s leading garden room company with over 20 years of experience and more than 17,000 installations completed nationwide and a 5-star Trustpilot rating.
Quality Materials and Design
Basebox by Green Retreats is a fully insulated garden room designed to offer a cost-effective solution for creating additional space at home. It is built using carefully selected materials chosen for their strength, durability and long-term performance.
Every element of the building, from the structural framework to the exterior cladding, is engineered to provide a solid, permanent feel and reliable everyday use.
Doors and Windows
All doors and windows in the Basebox range are manufactured from steel reinforced uPVC. Insurance grade multi point locking systems are fitted as standard to provide security and peace of mind.
Customers can choose between uPVC French doors or sliding doors, depending on their preferred layout.
Glazing
All windows and doors are fitted with Pilkington K Optiwhite extra clear double glazing. The glazing is argon filled and low emissivity coated, incorporating a Planitherm layer and Swisspacer bar to improve thermal performance.
This glazing system helps maintain comfortable internal temperatures and supports year-round use.
Walls and Insulation
Wall sections are manufactured in house using eco-friendly materials. Each wall features a 9mm white MDF internal board combined with 75mm eco polymer foam insulation to deliver excellent thermal efficiency.
The exterior is finished in a treated recycled composite cladding made from sawmill by-products. This cladding is resistant to rot and decay.
Please note: the exterior composite cladding requires painting within the first six months to seal the surface. This allows customers to personalise the colour and finish of their building.
Flooring
The Basebox floor is elevated above ground level to reduce the risk of rising damp and promote air circulation. The flooring system includes dense 80mm polyurethane insulation for thermal performance.
A 1mm powder coated steel layer is applied to both the top and underside of the floor structure, providing strength, durability and protection from weather conditions.
Roofing
The roof is constructed using an 80mm insulated steel panel system, reinforced with a 1mm powder coated steel layer. An additional 0.5mm galvanised steel sheet increases structural strength and durability.
The roof design incorporates a slight slope to allow effective water runoff to the rear guttering system and downpipe.
Guttering
A 4-inch-wide guttering system is fitted as standard to manage rainfall effectively and help protect the building structure.
Eco Friendly Construction
Green Retreats is an eco-friendly and carbon neutral company. Basebox garden rooms are designed and manufactured in the UK using sustainable construction methods and materials wherever possible.
All buildings are produced in a solar powered UK factory, and five trees are planted for every tree used in construction as part of Green Retreats’ environmental commitment.
Optional Extras
Optional extras allow you to personalise your Basebox garden room to suit your needs.
Foundations Pack
A suitable level base is required for all Basebox garden rooms. The Foundations Pack removes the need to organise this yourself or use a third-party contractor.
Our installation team will install a tried and tested polymer crate foundation system prior to your building installation date. This system is efficient, eco-friendly and designed to ensure your Basebox is perfectly level and ready for installation.
Floor Pack
The Floor Pack allows laminate flooring to be added to your Basebox garden room and professionally fitted by our installation team.
Customers can choose from oak, grey or white laminate flooring, providing a clean, durable finish that is ready to use as soon as installation is complete.
Paint Pack
The Paint Pack supplies your Basebox with three premium exterior paint options, allowing you to personalise the look of your building.
You can choose from modern black, smokey grey or chic sage green. The building must be painted using the supplied paint within six months to seal the exterior surface.
Deck Pack
The Deck Pack adds a practical and stylish deck step to the front of your Basebox garden room.
This improves access to the building and creates a neat transition between your garden and the interior space.
Electrics Pack
The Electrics Pack allows electrics to be installed as part of your garden room installation, providing power and lighting ready for everyday use.
You can choose from the following options:
Pack 1
• 2 surface mounted double sockets
• 1 panel light
• Consumer unit
• 1.5kW oil filled standing radiator
Pack 2
• 4 surface mounted double sockets
• 2 panel lights
• Consumer unit
• 1.5kW oil filled standing radiator
Pack 3
• 6 surface mounted double sockets
• 3 panel lights
• Consumer unit
• 1.5kW oil filled standing radiator
For more information, please email costco@greenretreats.co.uk or call 01296 328260.
| Brand | Green Retreats - Large |
| Type | Garden Room |
| Dimensions | 20m² – 28m² |
|






