50mm Insulation Board

Why 50mm Insulation?

50mm is one of the most widely specified rigid insulation thicknesses in UK construction and it works across an enormous range of applications. At this depth, PIR boards start to deliver the thermal resistance needed to make a real contribution to meeting Part L of the Building Regulations, which sets out the minimum energy efficiency standards for new builds and major refurbishments in England.

That makes 50mm the standard starting point for most wall, floor and roof insulation projects, whether you are building from scratch or upgrading an existing property. Here is what the range covers:

• PIR boards at 50mm achieve 0.022 W/mK thermal conductivity, suitable as a primary layer for walls, floors and roofs or as part of a multi-layer build-up
• Phenolic boards outperform PIR with a lambda as low as 0.019 W/mK, the right choice where build-up depth is tightly constrained and U-value targets are demanding
• EPS boards offer cost-effective performance at 0.038 W/mK for ground floors, external wall insulation systems and below-ground applications
• XPS boards deliver high compressive strength and negligible moisture uptake for inverted roofs, basements and heavily loaded floor slabs

50mm PIR Insulation Boards

PIR is the most popular choice for 50mm rigid insulation in the UK. Foil-faced, lightweight and easy to cut, PIR boards at 50mm are suitable for solid and suspended floors, framed wall systems, pitched roof applications between or below rafters and flat roof build-ups. All boards achieve a thermal conductivity of 0.022 W/mK.

Celotex GA4050

The Celotex GA4050 is one of the most popular 50mm PIR insulation boards in the UK. A multi-purpose board suitable for walls, floors and pitched roofs across domestic and commercial projects, it is BBA certified, simple to install and one of the most competitively priced options in the range. Feel free to browse the full Celotex insulation range for all board types and thicknesses.

Kingspan Therma Range

Kingspan makes three core PIR boards at 50mm, each designed for a specific application. Kingspan ThermaFloor TF70 is widely used beneath screed and above ground-bearing slabs and works with underfloor heating systems. Kingspan ThermaWall TW55 is the standard choice for timber and steel frame wall construction. Kingspan ThermaPitch TP10 is the go-to board for between-rafter and below-rafter pitched roof work. All three are available through the full Kingspan insulation range.

Recticel, Ecotherm and Unilin

The Recticel Eurothane GP at 50mm, Ecotherm Eco-Versal and Unilin PIR all share the same 0.022 W/mK thermal conductivity and foil-faced construction as the Celotex and Kingspan boards, making them solid alternatives where price or availability is a factor.

50mm Phenolic Insulation Boards

Where maximum thermal performance is needed within a limited build-up depth, phenolic boards at 50mm outperform PIR while taking up the same space. Kingspan Kooltherm K103 achieves a thermal conductivity of 0.019 W/mK and is widely used for floor insulation where keeping the floor level as low as possible matters.

For pitched roofs and loft conversions, Kingspan Kooltherm K107 delivers the same performance advantage for installation between the rafters. Phenolic boards are the right choice for projects where U-value targets are demanding and there is no room to increase the build-up depth. Both are available through the Kingspan Kooltherm range.

50mm EPS Insulation Boards

Expanded polystyrene is one of the most cost-effective options for 50mm floor and wall insulation where maximum thermal efficiency is not the main priority. Jablite Jabfloor EPS70 achieves a thermal conductivity of 0.038 W/mK and is BBA certified for domestic ground floor construction, well suited to solid concrete slabs, beam and block floors and external wall insulation systems.

The graphite-enhanced Jablite HP+ performs better, reaching 0.030 W/mK and delivers more thermal resistance in the same board thickness. Browse all 50mm polystyrene insulation including EPS and XPS boards in one place.

50mm XPS Insulation Boards

Extruded polystyrene at 50mm is the right choice where high load-bearing capacity and resistance to moisture are both essential. This makes it the specialist option for inverted flat roofs, basement walls and floor slabs exposed to damp or heavy loads. Ravatherm XPS is available in multiple grades through the Ravatherm XPS range. The 300SB grade suits domestic and medium load-bearing floors.

The 500SL grade is used for inverted roof structures and heavier floor slabs where the insulation sits above the waterproofing layer and must withstand foot traffic and imposed loads.

Where Is 50mm Insulation Used?

50mm floor insulation: Celotex GA4050 and Kingspan ThermaFloor TF70 below screed or between joists, both compatible with underfloor heating. Jablite EPS70 for standard domestic ground floor slabs. Ravatherm XPS where moisture resistance or load-bearing capacity is the priority.

50mm wall insulation: Celotex GA4050 and Kingspan ThermaWall TW55 for timber and steel frame construction, contributing to Part L wall U-value targets. Also widely used as a secondary layer in multi-layer wall systems.

50mm roof insulation: Kingspan ThermaPitch TP10 and Kooltherm K107 for between-rafter pitched roof applications, with phenolic boards delivering better thermal performance in the same rafter depth. Ravatherm XPS for inverted flat roofs where the insulation sits above the waterproofing layer.

Other Insulation Board Thicknesses

50mm is the starting point for many insulation projects, but the right thickness depends on your U-value target, available build-up depth and the application. Browse by thickness to find the right fit:

• 75mm insulation board for projects where 50mm does not achieve the required U-value and a single thicker layer is preferred
• 100mm insulation board the most popular single-board thickness for walls, floors and roofs across new build and refurbishment
• 150mm insulation board for high-performance and low-energy specifications where maximum thermal resistance is the priority

View all insulation boards to browse across all thicknesses, materials and brands in one place

Why Choose Insulation UK for 50mm Insulation?

Competitive Pricing: Some of the most competitive 50mm insulation board prices available online, including some of the most affordable options from trusted brands. No minimum order value on any product.

All the Leading Brands: Celotex, Kingspan, Recticel, Ecotherm, Unilin, Jablite and Ravatherm all stocked at 50mm and available 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: 50mm PIR half boards are available in a 1.2m x 1.2m format, ideal for smaller areas, awkward spaces and last-minute top-ups. Next-day delivery is available if ordered before 12pm.

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, whether you need guidance on U-value targets, application suitability, or which brand and thickness best fits your build-up.

Not sure which 50mm 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.