75mm Insulation Board

75mm Insulation Board Types and Applications

A 75mm insulation board is one of the most commonly specified rigid board thicknesses in UK construction, delivering the thermal resistance needed for Part L Building Regulations compliance across the majority of wall, floor, and roof scenarios. At this depth, PIR and phenolic boards can frequently perform as a standalone solution rather than a supplementary layer, making 75mm the go-to specification for ground floors under screed, between-rafter pitched roof builds, and framed wall systems in both new build and refurbishment. At Insulation UK, we stock the full range of rigid insulation boards at this thickness from all the leading manufacturers, with competitive trade pricing and fast UK-wide delivery on every order.

75mm PIR Insulation Boards

PIR insulation board at 75mm is the most widely used product in this range, offering a thermal conductivity of 0.022 W/mK in a foil-faced, lightweight format that is straightforward to cut and handle on site. At this depth, rigid PIR boards are suited to solid concrete and suspended timber floors, timber and steel framed wall systems, between-rafter pitched roof applications, and flat roof warm deck build-ups.
Celotex GA4075 is one of the most widely specified PIR boards at this thickness, delivering reliable thermal performance across walls, floors, and roof applications. For floor insulation specifically, Kingspan ThermaFloor TF70 is a popular choice for both solid and suspended floor constructions and is compatible with underfloor heating systems. Kingspan ThermaWall TW55 is widely used in timber and metal stud framing, while Kingspan ThermaPitch TP10 is a common specification for between-rafter and below-rafter pitched roof work. Recticel Eurothane GP, Ecotherm Eco-Versal, and Unilin PIR are also stocked at this thickness, all sharing the same 0.022 W/mK thermal conductivity and foil-faced performance.

75mm Phenolic Insulation Boards

Where maximum thermal performance within a fixed build-up depth is required, phenolic insulation board at this thickness outperforms PIR in an identical profile. Kingspan Kooltherm K103 achieves a thermal conductivity of 0.019 W/mK and is the preferred choice for floor insulation projects where floor level constraints make a thinner board essential. For pitched roofs and loft conversions, Kingspan Kooltherm K107 delivers the same performance advantage for between-rafter and below-rafter applications.
75mm Polystyrene Insulation Boards.

EPS Insulation Boards 75mm

Expanded polystyrene (EPS) is a competitively priced option for applications where the very highest thermal efficiency is not the primary requirement. Jablite Jabfloor EPS70 is BBA certified for domestic ground floor constructions and achieves a thermal conductivity of 0.038 W/mK, making it a reliable and cost-effective choice for below-screed installations. For commercial or industrial projects with higher compressive demands, Jablite also supplies Jabfloor at EPS100, EPS150, and higher grades at this thickness.

XPS Insulation Boards 75mm

Extruded polystyrene (XPS) at this depth offers the combination of high compressive strength and negligible moisture uptake needed for inverted flat roofs, below-ground basement walls, and heavily loaded floor slabs. Ravatherm XPS is available in three grades: the 300SB for domestic and medium load-bearing floors, the 500SL for inverted roofs and heavier floor structures, and the 700SL for very high load applications including cold stores and industrial floors.

Where is a 75mm Insulation Board Used?

Walls

Rigid insulation boards at 75mm are widely used in timber and steel framed wall constructions, fitted between studs or applied as a continuous layer across the inner face of the frame. Celotex GA4075 and Kingspan TW55 are both regularly specified in this application, contributing meaningfully to Part L wall U-value targets of 0.18 W/m²K for new build.

Floors

This is one of the most common thicknesses for ground floor insulation in new build and refurbishment work. Celotex GA4075 and Kingspan TF70 are frequently specified below screed or between suspended floor joists, while Jablite EPS70 and Ravatherm XPS provide alternatives where compressive performance or moisture resistance is the primary consideration.

Pitched Roofs and Loft Conversions

For between-rafter and below-rafter installations in pitched roof and loft conversion projects, PIR and phenolic boards at this depth deliver strong U-value performance without requiring excessive rafter depth. Kingspan TP10 and Kooltherm K107 are both frequently used for this work, with phenolic boards offering better thermal performance within the same rafter profile.

Flat Roofs and Below-Ground Applications

Ravatherm XPS boards at 75mm are well suited to inverted warm roof constructions where insulation sits above the waterproofing membrane and must withstand sustained moisture exposure and imposed loads. The 300SB and 500SL grades are also appropriate for basement perimeter walls and below-slab applications.

Why Choose Insulation UK for 75mm Insulation Boards?

Competitive Trade Pricing Including some of the most competitively priced 75mm rigid insulation boards available online, with no minimum order value.

All the Leading Brands Celotex, Kingspan, Recticel, Ecotherm, Unilin, Jablite, and Ravatherm, all stocked at this thickness and available at trade prices.

Fast UK-Wide Delivery Reliable delivery across the UK, with free shipping on orders over £500 (ex VAT).

Half Boards and Pre-Cut Strips Available PIR boards at this thickness are available as half boards and ready-cut joist strips, ideal for smaller areas and between-rafter or between-joist installations.

Expert Technical Support Our team has over 50 years of experience in the insulation industry. For help selecting the right board or guidance on achieving a specific U-value, call us on 03003 034 578.