For domestic concrete floors, a minimum thickness of 100mm of rigid PIR board is generally recommended to meet current building regulations. However, the exact thickness depends on the specific target U-value and the available floor height before making adjustments to skirting boards or doors.
Rigid Thermal Boards for Solid and Suspended Floors
This selection of floor insulation features rigid polyisocyanurate (PIR) boards designed to reduce heat loss across both solid concrete and suspended timber setups. Materials such as the Mannok Therm range offer low thermal conductivity, often reaching 0.022W/mK, to help meet BS EN 13165 standards for thermal efficiency. These boards are widely applied in new builds, extensions, and renovation work where ground-bearing floors require effective heat retention. In solid floor constructions, placing the insulation layers securely above damp proof membranes is standard practice to prevent ground moisture from entering the thermal barrier and the surrounding building fabric.
These rigid foam products are compatible with underfloor heating systems, helping to push warmth upwards into the room rather than letting it escape into the ground. Because the boards feature a low emissivity composite foil facing, they reflect heat efficiently while offering enough compressive strength to handle standard domestic floor loads. To ensure a continuous thermal and vapour barrier across the entire surface, the tight joints between individual sheets are typically sealed using foil tape, preventing cold bridging and moisture penetration before any screed or finished flooring is laid over the top.
When working with suspended timber floors, the panels are easily cut to size to fit snugly between wooden joists. This stops draughts from the ventilated sub-floor while maintaining the required airflow beneath. Once the insulating layer is firmly in position, the framework is frequently covered with structural OSB to create a stable, load-bearing deck that is ready for carpet, laminate, or tiling. The straightforward installation process and the ability to cut boards cleanly on site allow projects to achieve strict compliance with modern thermal building regulations.
Floor Insulation FAQ's
Cutting and fitting rigid foam boards is a straightforward process. Measuring the required size and using a fine-toothed hand saw to cut the panels will yield clean results. When fitting them between timber joists, a snug friction fit is necessary to prevent heat from escaping through gaps.
It is always recommended to manage moisture when insulating ground-bearing setups. Placing a durable polythene sheet beneath the insulation helps protect the material from ground moisture, while taping the joints of foil-faced boards provides an effective vapour control layer on the warm side.
To keep boards firmly in place without sagging, timber battens can be installed along the inside edge of the joists to support the panels from underneath. Alternatively, special saddle clips or insulation netting can be used to hold the rigid sheets securely flush with the top of the joists.
Underfloor heating pipes are frequently installed directly on top of foil-faced insulation panels. Securing the pipes involves using plastic holding clips that push straight into the rigid foam surface. This setup ensures the heat is directed upwards into the room, rather than being absorbed and lost into the subfloor below.