Off-site Construction
Updated: 1 December 2025
Reading Time: 4 minutes
When buying a garden room, there are three main approaches to installing the building in your garden. In some cases, the company will deliver materials to your home and construct the room from scratch on-site. This is known as on-site construction.
Another method is to manufacture the building in a factory and deliver it to your site in modules, which are then assembled in your garden. This is referred to as off-site construction.
A third option, offered by some companies, involves fully constructing the garden room in a factory, including all exterior and interior finishes. The completed building is then transported to your site on a lorry and craned onto a pre-prepared foundation.
Off-site construction is by far the most common method used in the garden room industry.
Approaches to Off-site Construction
There are two approaches to off-site construction within the garden room industry. Some companies have their own workshops or factories where they manufacture the buildings in-house. Others do not have manufacturing units and instead source the different elements from various suppliers, managing the project to ensure all parts arrive on-site when needed.
In-house Manufacturing
Leading names in modular garden room design often have their own factories where they produce the modules that form the rooms.
These factories are organised into stations, each specialising in different aspects of the build. By the time the modules leave the factory, they are almost complete, often with windows installed and interior finishes applied.
The modules are designed in manageable sizes so that one or two installation team members can easily manoeuvre them into position on-site.
Once the installation date arrives, the modules and other building components are loaded onto lorries and delivered to your address. The company's in-house installation teams then transport the modules from the lorry to your garden and begin assembling your garden room.
Outsourcing Manufacturing
When buying a garden room with a SIPs (structural insulated panels) core, the designer often sends the plans to a specialist SIPs manufacturer, who cuts the panels to size and delivers them to your site when required.
This approach often extends to other parts of the build. For example, doors and windows might be sourced from one supplier, and exterior cladding from another.
This type of off-site construction requires strong relationships with suppliers and excellent project management skills. Timely delivery of materials is crucial to keeping the on-site build phase on schedule.
Explore the Work of the Garden Room & Annexe Companies That Work in Your Area
International Off-site Construction
Most garden room companies manufacture their products in the UK. However, some companies have manufacturing units overseas. For example, Garden2Office specialises in Swedish-manufactured garden rooms.
Eastern Europe is also a popular location for garden building manufacturing. Many of the sheds and log cabins sold in the UK are made in Eastern Europe, and in recent years, they have expanded their portfolios to include insulated garden rooms, you will often find these ranges on the online garden building marketplaces.
Fast Installation
One of the key benefits of off-site construction is the speed of installation. By completing the majority of work before the installation team arrives, projects can be completed much more quickly.
Building a garden room is one of the fastest ways to extend your home. A small modular garden room can often be installed in just one day, while larger, more complex projects typically take 2-3 weeks, with teams on-site Monday to Friday.
Built in Optimal Conditions
Off-site manufacturing allows companies to control the conditions in which their garden rooms are built, avoiding the challenges posed by the British weather.
If a room were built from scratch on-site, various layers could be exposed to the elements, which might compromise its structural integrity if rainwater seeps in. By contrast, off-site construction ensures that much of the work is carried out indoors, in dry, temperature-controlled environments.
For example, if you choose a garden room with a painted finish, the paint is applied in ideal conditions, which improves the longevity of the finish.
Access to Precision Equipment
On-site construction teams set up temporary workshops with the tools they need. However, they do not have access to the precision machinery available in off-site construction facilities.
Some off-site manufacturers use large CNC machines that cut and shape timbers with millimetre accuracy. These machines are used not only for the structural elements but also for finishing details, such as cutting precise openings for electrical sockets.
In these factories, you’ll find stations set up for specific tasks, with jigs and templates ensuring each module is identical to the one before.
Access to Specialists
Another advantage of off-site construction is access to skilled workers. Factories are staffed with specialists in carpentry, painting, and electrical work, among other trades.
For instance, electricians will pre-wire the wall modules before they leave the factory, ensuring that once the garden room is assembled on-site, the electrics are ready to be connected to the main supply in your home. This final connection is often left for you to arrange with a local electrician, as it’s more efficient for the company’s in-house electricians to remain in the workshop, wiring up multiple garden rooms each week.
Cost Efficiency
Off-site construction benefits from precision machinery and skilled in-house workers who can contribute to several projects at once. Additionally, completing most of the work in a factory reduces the time spent on-site, which can be costly due to travel and accommodation expenses.
By minimising the on-site phase, companies can lower costs while maintaining quality.
Fully Factory Built Garden Rooms
Some companies fully assemble their garden rooms in the factory before transporting them as complete units. This method requires careful planning, as the building must be constructed on a steel frame to allow for safe lifting.
This approach offers a quick transformation: the room can be delivered and installed in just a few hours. An added benefit is that the building can potentially be moved to a new location if you decide to relocate, as it can be lifted and transported in the same way it was initially delivered.
