40mm Kingspan Kooltherm K103 Floorboard is a rigid thermoset phenolic floor insulation board, supplied as a pack of 8 sheets covering 23.04m². At 40mm it is the second-thinnest board in the K103 range, the option where the 25mm does not give enough resistance but the floor build-up still has to stay shallow: refurbishment floors, extensions, and upgrades to existing concrete or timber floors where every millimetre of depth counts.

Each square-edge board measures 2400mm x 1200mm and covers 2.88m², so the 8-board pack provides 23.04m² of coverage to plan a floor around. The phenolic core runs at a thermal conductivity of 0.019 W/mK and gives the 40mm board a thermal resistance of 2.10 m²K/W, a clear step on from the 1.30 m²K/W of the 25mm. Both faces carry a glass tissue based facing, autohesively bonded to the core during manufacture.

With a compressive strength of 120 kPa, the board takes the load of a screed and normal floor traffic once the floor is finished. That lets the 40mm be laid below the screed or below a slab across a floor area and built over in the usual way, while the offset break-bonded layout keeps the insulation continuous beneath the finished surface.

40mm Kooltherm K103 is used in beam and dense block ground floors, suspended timber ground floors and solid concrete ground floors, set below the screed, below the slab or between the joists according to the construction. It is laid over a damp proof membrane, fitted in line with Kingspan's guidance and the project specification, and is not installed directly over timber joists. It suits new build and refurbishment across domestic, commercial and industrial floors, and works with underfloor heating systems.

Key Benefits of Kingspan Kooltherm K103:

• Pack of 8 boards covering 23.04m², for insulating a floor area in one order.
• 40mm rigid thermoset phenolic floor board, the second-thinnest profile in the K103 range.
• Thermal resistance (R-value) of 2.10 m²K/W, a step up from the 25mm board's 1.30 m²K/W.
• Thermal conductivity of 0.019 W/mK, among the lowest available for rigid floor insulation.
• Compressive strength of 120 kPa, taking screed and normal floor loads once the floor is finished.
• Square-edge boards faced both sides with glass tissue, autohesively bonded in manufacture.
• 2.4m x 1.2m boards at 2.88m² each, giving 23.04m² of planned coverage per pack.
• Suitable for beam and block, suspended timber and solid concrete floors, below slab or screed.
• More resistance than the thinnest board while keeping the floor build-up shallow, for refurbishments and extensions.
• Compatible with underfloor heating, and suited to both new build and refurbishment.

Good to know:

• The boards need a damp proof membrane beneath them (minimum 1200 gauge polythene) and should not sit in direct contact with subsoil.
• The board resists the passage of water vapour but does not act as a vapour control layer; under a screed, overlay it with a separate lapped and taped polythene sheet to form the VCL.
• It is not fixed directly over timber joists; in a suspended floor it sits between the joists on battens, saddle clips or nails.
• At 40mm the 2.10 m²K/W resistance is a useful upgrade layer, but check the full floor build-up against your target U-value before ordering pack quantities.

For a floor that needs more than the thinnest board but little extra depth, the 40mm pack puts 23.04m² of K103 on site in one go.