50mm Insulation Board

50mm Insulation Board Types and Applications

A 50mm insulation board is one of the most widely specified thicknesses in UK construction and is the standard starting point for most wall, floor, and roof insulation projects. At this thickness, PIR boards begin to deliver the thermal resistance levels needed to make a meaningful contribution to U-value targets under Part L of the Building Regulations, making 50mm the go-to choice for both new build and refurbishment work. At Insulation UK, we stock 50mm insulation boards from all the leading manufacturers, with trade prices and fast UK-wide delivery on every order.

50mm PIR Insulation Boards

50mm PIR insulation board (polyisocyanurate) is the most popular choice at this thickness, delivering a thermal conductivity of 0.022 W/mK. Most boards in this range are foil-faced, lightweight, easy to cut, and suitable for roofs, walls, floors, and loft applications.
At 50mm, PIR boards are a practical primary insulation solution for solid concrete floors, timber frame walls, pitched roof between-rafter applications, and flat roof warm deck build-ups. The thickness makes them equally suited to new build projects targeting Part L compliance and refurbishment work where meaningful thermal uplift is required.
Popular choices include Celotex GA4050, Kingspan Therma TF70, TP10 and TW55, Recticel Eurothane GP, Ecotherm Eco-Versal, and Unilin.

50mm Phenolic Insulation Boards

For applications where thermal performance must be maximised within a fixed build-up depth, phenolic insulation board at this thickness outperforms PIR in an identical profile. Kingspan Kooltherm K103 achieves a thermal conductivity of 0.019 W/mK at 50mm, and the K107 pitched roof board offers the same performance advantage for loft conversion and rafter applications. Phenolic boards at this thickness are the preferred choice for projects with demanding U-value targets where increasing the overall build-up depth is not an option.

50mm Polystyrene Insulation Boards

EPS Insulation Boards 50mm

50mm polystyrene insulation board in expanded polystyrene (EPS) form is a cost-effective option for applications where the very highest thermal performance is not the primary requirement. Boards in this grade are well suited to ground floors, external wall insulation systems, and below-ground applications. For those looking for competitively priced 50mm insulation board options without compromising on reliability, expanded polystyrene is one of the most competitively priced choices available. Jablite Jabfloor EPS70 is available for floor applications across domestic and commercial builds.

XPS Insulation Boards 50mm

50mm extruded polystyrene (XPS) board combines high compressive strength with superior long-term moisture resistance, making it the specialist choice for inverted flat roofs, below-ground basement applications, and areas with sustained moisture exposure. Ravatherm XPS is available in multiple grades and delivers a thermal conductivity of 0.030 W/mK with negligible moisture uptake even in wet conditions.

Where is a 50mm Insulation Board Used?

Walls

50mm PIR insulation boards are widely used in timber and steel framed wall constructions, fitted between the studs or between the frame and the internal lining board. At this thickness, boards such as the Celotex GA4050 and Kingspan TW55 contribute meaningfully to achieving Part L wall U-value targets of 0.18 W/m²K for new build.

Floors

These boards are a popular choice for solid concrete and suspended timber floor insulation, installed either below the screed or between the joists. Kingspan TF70 and Celotex GA4050 are widely specified for floor applications at this thickness, while Jablite EPS70 and Ravatherm XPS offer alternatives where moisture resistance or compressive strength is the primary consideration.

Pitched Roofs and Loft Conversions

PIR and phenolic boards at 50mm are commonly installed between and below rafters in pitched roof and loft conversion projects. Kingspan TP10 and Kooltherm K107 are popular choices, with phenolic boards delivering better U-values in the same rafter depth.

Flat Roofs

XPS boards from Ravatherm are well suited to inverted warm roof applications where the insulation sits above the waterproofing membrane and must resist sustained moisture exposure and foot traffic loads.

Why Choose Insulation UK for 50mm Insulation Boards?

Competitive Trade Pricing Including some of the cheapest 50mm insulation board prices available online, with no minimum order value.

All the Leading Brands Celotex, Kingspan, Recticel, Ecotherm, Unilin, Jablite, and Ravatherm, all stocked at 50mm 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 Available 50mm insulation boards available as half boards for smaller areas and last-minute orders

Expert Technical Support Our team has over 50 years of experience in the insulation industry. Whether you need help selecting the right board for your project or guidance on achieving a specific U-value, get in touch and we will point you in the right direction.