How to Insulate Concrete Flooring

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Insulating a fresh concrete slab

The process begins with choosing the right type of insulation material. Common options include rigid foam boards, such as extruded polystyrene (XPS) or expanded polystyrene (EPS), which are effective at preventing heat loss and providing a moisture barrier. These materials are dense, durable, and capable of withstanding the weight of the concrete floor.

To insulate a concrete floor, start by ensuring the subfloor is clean, level, and dry. Next, lay a damp-proof membrane (DPM) over the subfloor to protect against moisture from the ground. The rigid foam insulation boards are then placed on top of the membrane, fitting them snugly together without gaps to prevent thermal bridging. If additional thermal resistance is required, a second layer of insulation can be added, with the joints staggered to improve the overall insulation performance.

Once the insulation is in place, another layer of a damp-proof membrane may be added to further protect against moisture. After that, a screed (a thin layer of concrete or mortar) can be poured over the insulation to create a smooth, level surface for your final flooring material, whether it’s tile, wood, or carpet. This screed also helps to protect the insulation from damage. For underfloor heating systems, the heating elements can be installed above the insulation but below the screed, ensuring that the heat is directed upwards into the room rather than being lost to the ground. Properly insulating a concrete floor not only helps to reduce energy costs but also improves the overall comfort of the space by minimizing heat loss and cold spots.

Can you insulate an existing concrete slab?

Insulating an existing slab typically involves adding a layer of insulation on top of the concrete, followed by a new flooring system. This approach helps to improve the thermal efficiency of the space and reduce heat loss through the floor.

To insulate an existing concrete slab, start again by cleaning the surface to remove any debris. Once the slab is clean and dry, you can install a damp-proof membrane (DPM) to prevent moisture from penetrating the insulation layer. Next, lay rigid foam insulation boards, such as extruded polystyrene (XPS) or expanded polystyrene (EPS), directly on top of the slab. These boards should be cut to fit snugly against each other, with no gaps, to ensure effective insulation.

After the insulation is in place, you have a few options for the final flooring layer. You can pour a thin layer of screed over the insulation to create a smooth, level surface for your chosen floor finish, whether it's tile, wood, or carpet. Alternatively, you can install a floating floor system, where the flooring material is laid directly on top of the insulation, using an underlayment for additional support and moisture protection.

Insulated concrete floor for a bathroom
Insulated concrete floor for a bathroom

How much heat is lost through a concrete floor?

Concrete is a dense material that has relatively high thermal conductivity, meaning it can transfer heat quickly. In an uninsulated concrete floor, a substantial amount of heat can be lost to the ground, particularly in colder climates.

Studies and estimates suggest that up to 10-15% of a building's total heat loss can occur through an uninsulated concrete floor. This figure can be higher in cases where the floor is in direct contact with the ground and no damp proof membrane or insulation is present. In contrast, properly insulating the concrete floor can significantly reduce heat loss, improving energy efficiency and reducing heating costs. Insulation acts as a barrier, preventing heat from escaping through the floor and keeping the living space warmer and more comfortable.

An insulated polished concrete floor for a kitchen.
An insulated polished concrete floor for a kitchen.

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