Large SIP Garden Room with Storage in Chiswell Green
A bespoke garden room designed for year-round use
This bespoke garden room in Chiswell Green, Hertfordshire was designed as a spacious, modern outdoor building that combines a bright main room with a separate internal storage area. The project uses a clean contemporary design, practical internal layout and a high-quality SIP structure to create a garden room suitable for everyday use throughout the year. The overall size of 8.20m x 4.00m, with the building constructed using SIP panels for the base, walls and roof.
The design brings together a warm Thermowood front elevation, dark anthracite side and rear finishes, full-height glazing to the front, a front canopy, internal plastered finishes, fitted electrics and a dedicated storage room built into the same structure.
Project Overview
This project was designed for a client who needed more than a basic garden building. The brief was to create a larger, high-performance garden room with a practical internal layout, strong insulation values and the flexibility to serve different uses over time. The result is a bespoke SIP garden room that combines everyday comfort with a clean, modern architectural appearance.
Externally, the building has a striking contemporary front elevation finished with vertical Thermowood cladding and a generous glazed section that allows plenty of natural light into the main space. The design gives the garden room a strong visual presence while still feeling refined and well balanced within the setting. Behind the finished exterior is a Structural Insulated Panel system chosen for its strength, insulation performance and long-term durability, helping to create a room that can be used comfortably throughout the year.
Internally, the layout was planned to maximise usable space while keeping storage separate and organised. The main room extends across most of the footprint, creating a bright and versatile open area suitable for a range of uses, while a dedicated storage section is positioned to one side of the building. As shown on the pictures, the storage area measures approximately 3.7m x 1.2m, allowing the client to keep practical items contained without compromising the quality or openness of the main room.
Size and Layout
The building is based on an overall footprint of 8.20m x 4.00m, making it a generous garden room suitable for a range of uses. The internal layout includes:
- a bright main room
- a separate internal storage area
- a standard access door to the store
- front-facing French doors into the main space

Future-Ready Services
One of the standout points in this project is that it was designed with future flexibility in mind. In addition to the main electrical setup, the quotation includes:
- power supply isolator for a future AC unit to be installed by the customer
- 10mm power cable for a future shower, hidden and not terminated
- 3-core cable for a future extractor fan, hidden and not terminated
- upgrade from 6mm armoured cable to 16mm to support an electrical shower later if needed
Foundation System
This project is specified with a screw pile foundation, including extra-long 2000mm screws at the front and 1250mm screws elsewhere, based on the site requirements. That gives the structure a practical engineered foundation solution while reducing the amount of traditional excavation needed.
Built with SIP Panels
The core of this project is the SIP panel structure, used for the base, walls and roof. The materials section explains that Structural Insulated Panels are a high-performance construction system made from an insulating core bonded between structural facings such as OSB. According to the quotation, this creates a building system that is strong, energy efficient and cost effective.
For the client, this means the garden room is designed to offer:
- strong structural performance
- better insulation than many basic outbuildings
- a more comfortable internal environment
- a building suitable for regular everyday use
This is one of the key reasons SIP garden rooms feel closer to a proper extension-style space than a lightweight garden building.
Integrated Storage Room
The internal storage room is a key part of this design. Rather than using up garden space with a second outbuilding, this project builds the store directly into the same structure. The specification notes an internal partition to create a 3.7m x 1.2m storage room with a standard door, making it easy to separate practical storage from the main finished room.
This is ideal for tools, seasonal items, garden equipment or general household storage, and helps the main room stay cleaner and more usable.
Interior Finish
Inside, the project was designed to be fully finished and ready to use. The specification includes:
- internal plasterboard and skim
- white Dulux paint
- Howdens laminate flooring
- white skirting
- Howdens 4-panel shaker internal doors
This gives the interior a clean, modern and practical finish suited to both work and leisure use.
External Finish and Design
The exterior design gives this project a modern and balanced look. The front of the building is clad in Thermowood, while the sides and rear are finished in cement particle boards painted Grey Anthracite RAL 7016. This mix of natural timber and darker side elevations creates a smart contrast and helps the building look more architectural and premium than a standard shed-style garden room.
The external specification also includes:
- EPDM roof membrane
- black guttering to the rear
- 400mm canopy above the front elevation
- modern anthracite-coloured joinery to the glazed front section
Doors and Windows
This garden room includes a front glazed section designed to maximise daylight into the main room. The quoted specification includes:
- 1 PVC French door set, approximately 1600mm wide x 2030mm high
- 2 side fixed-frame windows, approximately 800mm x 2030mm
- grey anthracite outside and white inside finish
This combination gives the building a bright and open internal feel while keeping the external appearance sharp and modern.
Lighting and Electrical Specification
This project includes a strong electrical package designed for practical daily use. The specification includes:
- 8 internal LED downlights in the main room
- 1 surface LED light in the storage room
- 4 LED lights to the outside canopy
- 6 white double sockets
- consumer unit
- free internet cable
- supply and fit armoured cable
This gives the client a garden room that is ready for work, leisure or multi-purpose use from the start, while also supporting future upgrades.
Why This Project Stands Out ?
This garden room stands out because it combines size, appearance and practicality in one well-balanced design. It offers:
- a large 8.2m x 4m footprint
- SIP construction for year-round performance
- Thermowood cladding to the front
- anthracite side and rear finishes
- a bright glazed front elevation
- a separate internal storage room
- full internal finishing
- strong electrical specification
- future-ready cabling for further upgrades
It is a very good example of how a bespoke SIP garden room can be designed not just to look impressive, but also to work hard for the client over the long term.
Thinking About a Similar Garden Room?
At TRJ Construction, we design and build bespoke SIP garden rooms tailored to the way you want to use the space. Whether you want a larger garden office, studio, gym, hobby room or multi-purpose building with separate storage, we can create a structure that looks smart, performs properly and feels like a real extension of your living space.
Looking for a bespoke SIP garden room in Hertfordshire or beyond?
Get in touch with TRJ Construction to discuss your ideas, layout, finishes and design options.
