100mm Insulation Board

Why 100mm Insulation Boards?

100mm is one of the most widely specified rigid insulation thicknesses in the UK and for good reason. At this depth, a single layer of PIR or phenolic board can often deliver the thermal resistance needed to meet Part L Building Regulations targets across walls, floors and roofs without requiring a secondary layer.

That makes 100mm the default specification for many new build and refurbishment projects where performance and build-up depth both matter. Here is what the range covers:

Single-layer solution for Part L compliance in many wall, floor and roof applications

• PIR boards at 100mm achieve 0.022 W/mK thermal conductivity, minimising build-up depth
• Phenolic boards at 100mm outperform PIR with a lambda as low as 0.019 W/mK for the tightest spaces
• EPS options available at 0.030 to 0.038 W/mK for cost-effective floor and wall applications
• XPS at 100mm delivers the high compressive strength and moisture resistance needed for inverted roofs and below-ground use
• Available as half boards for smaller areas, awkward cuts and last-minute top-ups

100mm PIR Insulation Boards

PIR (polyisocyanurate) is the most commonly specified material for 100mm rigid insulation in the UK. Foil-faced, lightweight and easy to cut, PIR boards at this thickness are suitable for solid and suspended floors, framed wall systems, pitched roof applications and flat roof warm deck build-ups. All boards achieve a thermal conductivity of 0.022 W/mK and are non-water absorbent, meaning performance is maintained across damp or humid environments.

Celotex GA4100

The Celotex GA4100 is one of the most frequently ordered 100mm PIR insulation boards in the UK. Positioned by Celotex as their general application board, it is suitable for walls, floors and pitched roofs in both domestic and commercial projects. BBA certified, lightweight and simple to install, it is a reliable and cost-effective choice for most standard 100mm specifications. Browse the full Celotex insulation range for all board types and thicknesses.

Kingspan Therma Range

Kingspan produces several 100mm PIR boards, each optimised for a specific application and each is optimised for a specific application. Kingspan ThermaFloor TF70 is widely used beneath screed and above ground-bearing slabs and is compatible with underfloor heating systems. Kingspan ThermaWall TW55 is the go-to board for timber and steel frame wall systems. Kingspan ThermaPitch TP10 is a standard specification for between-rafter and below-rafter pitched roof work. All three are available through the full Kingspan insulation range at Insulation UK.

Recticel, Ecotherm and Unilin

Recticel Eurothane GP, Ecotherm Eco-Versal and Unilin PIR complete the 100mm PIR range. All share the same 0.022 W/mK thermal conductivity and foil-faced construction as the Celotex and Kingspan equivalents, making them practical alternatives where price or availability is a consideration. Browse all PIR insulation boards to compare brands and specifications.

100mm EPS Insulation Boards

Expanded polystyrene is one of the most competitively priced options for 100mm floor and wall insulation where the very highest thermal efficiency is not the primary concern. Jablite Jabfloor EPS70 achieves a thermal conductivity of 0.038 W/mK and is BBA certified for domestic ground floor construction.

The graphite-enhanced Jablite HP+ improves on this with a lambda of 0.030 W/mK, offering better performance in the same footprint. For higher loads, Jablite Jabfloor EPS100 is suited to offices and schools, while higher compressive strength grades are available for heavy commercial and industrial floor applications where imposed loads are a factor.

100mm XPS Insulation Boards

Extruded polystyrene at 100mm provides the combination of high compressive strength and negligible moisture uptake required for inverted flat roofs, basement walls and heavily loaded floor slabs. Ravatherm XPS 300SB is suited to domestic and medium load-bearing floors. Ravatherm XPS 500SL is the specification for inverted roof structures and heavier floor build-ups. Ravatherm XPS 700SL covers the most demanding applications including cold store floors and industrial slabs. Browse the full Ravatherm XPS range for all grades and thicknesses.

Where Is 100mm Insulation Used?

100mm floor insulation: Celotex GA4100 and Kingspan ThermaFloor TF70 below screed or between joists, both compatible with underfloor heating. Jablite EPS70 and Ravatherm XPS 300SB where compressive strength or moisture resistance is the priority.

100mm wall insulation: Celotex GA4100 and Kingspan ThermaWall TW55 for timber and steel frame construction, contributing to the 0.18 W/m2K Part L wall U-value target in a single layer.

100mm roof insulation: Kingspan ThermaPitch TP10 and Kooltherm K107 for between-rafter pitched roof applications. Celotex GA4100 for flat roof warm deck build-ups. Ravatherm XPS 500SL for inverted roofs where load and moisture resistance are the deciding factors.

Why Choose Insulation UK for 100mm Insulation?

Competitive Trade Pricing: Some of the most competitively priced 100mm rigid insulation boards available online, with no minimum order value. Whether you need one board or a full pallet, you will get a fair price.

All the Leading Brands: Celotex, Kingspan, Recticel, Ecotherm, Unilin, Jablite and Ravatherm all stocked at 100mm and available at competitive prices across PIR, phenolic, EPS and XPS.

Fast UK-Wide Delivery: Reliable delivery across the UK with free shipping on orders over £500 (ex VAT). Get the boards you need, when you need them.

Half Boards Available: PIR boards at 100mm are available as half boards for smaller areas, awkward spaces and last-minute top-ups, with express and next-day shipping options available.

Expert Technical Support: Our team has over 50 years of combined experience in the insulation industry and can help you choose the right board for your project.

Not sure which 100mm insulation board suits your project? Call us on 03003 034 578 or get in touch online and our team will help you find the right specification.