Insulated Concrete Base for a Garden Room: Why You Need One and How We Build It

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Garden rooms have become increasingly popular as versatile spaces that can serve as home offices, gyms, or even just a serene retreat. While the design and aesthetics of a garden room get much attention, its foundation is equally crucial. An insulated concrete base not only provides a strong foundation but also contributes significantly to the room’s energy efficiency. In this blog post, let’s explore why an insulated concrete base from Nucrete is an excellent choice for a garden room and how we go about constructing one.

Contact us if you’d like a free, no-obligation quote for an insulated concrete base for a garden room

Why Choose an Insulated Concrete Base?

Energy Efficiency

Insulating the concrete base will reduce the amount of heat lost through the floor, making your garden room much more energy-efficient. This is particularly beneficial in the UK climate where heating costs can quickly add up. It also saves having to fit a timber sub-floor that is susceptible to rot. You can build your garden room straight off the insulation concrete base which is much more cost effective.

If, on the other hand your garden room has a timber sub-base included much like those buildings from Dunster House and some other manufacturers, we can install a concrete base for a garden room without the insulation, should you prefer.

Increased Comfort

Although heat is lost through the walls and roof as well as the floor, an insulated base helps in maintaining a consistent internal temperature because of its thermal mass, making the garden room more comfortable to use year-round. Not only that, it makes for a much nicer feel under foot, especially if you remove your shoes. Because the insulation is below the concrete, it makes life much easier if you later wish to tile the floor as timber sub-floors can move and cause the tiles to crack if they are not rock solid.

Moisture Barrier

Insulation acts as an additional barrier against ground moisture, providing an extra layer of protection for your garden room. Having said that, we fit a DPM (Damp Proof Membrane) to every insulated concrete base we install.


With growing concerns about climate change, an insulated base is an eco-friendly option that minimizes your carbon footprint by reducing energy consumption. It also provides energy savings for the lifetime of the building for a relatively small initial outlay.

Planning and Preparation

Site Assessment

Try and choose a flat area in your garden to build the room if possible. An ideal situation is that the ground is reasonably firm and free from any drainage issues, although we always dig out to provide a solid sub-base before the insulation and concrete is laid. Grading of the surrounding land can also help with drainage issues which we will do if required. We perform a thorough site clearance, removing all vegetation and debris before any sub-base material is added.


If you require a level access for your building, we can provide a finished base height that will match the surrounding finished level of your garden or patio area. We will create a drainage channel across door thresholds to adhere with regulations and best working practices.

Typical Installation Process

Step 1: Decide on the Area

Once you have decided on the position, we use ground marking paint to outline the dimensions of the garden room. We double-check the measurements with you to make sure they’re accurate.

Step 2: Excavation

We excavate the marked area to the depth required with a mini-excavator. Normally, a depth of around 100mm to 200mm should suffice for most garden rooms dependant on your requirements. Spoils are either removed from site or spread over your land dependant on your requirements

Step 3: Install a Sub-Base

A layer of Type 1 MOT hardcore will act as a sub-base to a minimum thickness of 100mm, providing additional stability. Compaction of this layer is carried out using a mechanical compactor.

Step 4: Prepare the Shuttering

A wooden frame is crafted around the perimeter where the concrete will be poured, ensuring that it is level and secure. This will act as a mold for the concrete.

Step 5: Install the DPM

The damp proof membrane is laid over a blinding of sand on the sub-base. If you live in an area subject to gas release from the ground, we will use an approved gas membrane.

Step 5: Lay the Insulation Boards

We place the PIR insulation boards on top of the DPM and ensure that they fit snugly against each other to minimize heat loss through gaps. A gap of approximately 50mm will be left around the perimeter of the base to allow for encapsulation of the insulation. This small encapsulation gap reduces cold bridging to a minimum. PIR of different thicknesses can be chosen dependant upon your requirements, usually 70mm or 100mm PIR boards are recommended.

Step 6: Reinforcement

All insulated bases are reinforced using fibre reinforcement mixed into the concrete. This much improves the strength of the concrete for its lifetime.

Step 7: Pour and Level the Concrete

We pour ready-mixed concrete into the formwork, then using a tamp to level the concrete we make sure it’s flush with the top of the formwork. The finish is ready to accept a floor screeding compound after your garden room has been built to create a completely flat surface ready for your prefered flooring material.

Step 8: Curing

Allow the concrete to cure for at least a week. Keep the surface damp to avoid cracking if the whether is hot. After it has cured, you can remove the shuttering.


Building an insulated concrete base for your garden room is a smart decision that pays off in terms of comfort, energy efficiency, and sustainability.

It may seem like an arduous task, but with careful planning and execution, we can lay a foundation that stands the test of time and lasts beyond the lifespan of the building. Whether you’re planning to use your garden room as an office, a gym, or a sanctuary to relax, starting with a well-insulated base will ensure you get the most out of your new space.

Get in touch if you would like to discuss your insulated base needs further, we’re always happy to help with any questions or queries you might have.

Contact us for a no-obligation quote or more information…