120mm Celotex XR4120 PIR Insulation Board 2400mm x 1200mm

Product Overview

Foil-faced PIR insulation board for use in floors, walls, and roofs. 

Part of the XR4000 range, it provides extra resistance through increased thickness, helping achieve low U-values with a single board layer. 

At 120mm thick, this board is a common choice for achieving strong thermal performance in deeper cavities or roof constructions.

Features & Benefits

• Thermal conductivity (0.022 W/m·K): Reduces the thickness required to meet U-value targets.
• Low-emissivity foil facings: Reflect radiant heat across cavity air spaces, improving overall efficiency.
• XR4000 range (extra resistance): Suited to achieving low U-values with a single layer in roofs, walls, and floors.
• Rigid PIR core: Lightweight yet robust, easy to cut and install with standard tools.
• Moisture resistance: Closed-cell core prevents water uptake and preserves thermal performance.
• Environmental credentials: Zero ODP, low GWP blowing agent, and BRE Green Guide Rating A.
• BBA certified (17/5405, 16/5352): Independent assurance of performance across roofs, walls, and floors.
• Board size 2400 x 1200mm: Large-format sheets reduce installation time.
• Thickness 120mm: Practical thickness for achieving low U-values in roof and wall applications.
  
  

Applications

• Extra resistance: Thick board designed to achieve low U-values in single-layer applications for energy-efficient and low-energy projects.
• Beam & Block Floors: Rigid PIR insulation is laid directly over the floor structure to provide high thermal performance in limited floor thicknesses.
• Concrete Slab Floors: Boards are installed either above or below the slab to create a continuous thermal barrier and prevent heat loss into the ground.
• Suspended Timber Floors: Precision-cut boards are fitted between floor joists to significantly reduce draughts and improve the energy efficiency of the floor.
• Upgrading Concrete Slab Floors: The high thermal-to-thickness ratio allows for effective insulation upgrades over existing slabs where floor heights are restricted.
• Timber Frame Wall: Insulation is installed within the stud cavity or as a continuous layer to achieve low U-values in modern timber frame constructions.
• Between and Over Rafters: Boards are combined within and across the rafters to eliminate thermal bridging and create a high-performance warm roof.
• Between and Under Rafters: The insulation is fitted between rafters with a second layer underneath to maximise internal thermal retention in pitched roof spaces. 
• Pitched Roof Sarking: Large format boards are installed over the rafters to provide a seamless layer of insulation that protects the internal structure.
• Loft Insulation: The boards provide a stable, non-compressible surface suitable for supporting typical storage loads when used in conjunction with protective timber boarding and a load-bearing structure.
• New Build Roof Insulation: Specified for new build projects where Part L 2021 requires enhanced U-values and achieves optimal thermal performance when combined with additional layers.
• Passive House & Low-Energy Builds: Specified in passive house and low-energy building projects where maximum insulation performance per millimetre is essential.

Installation Guidance

• Cut and fit tightly: Use a knife or fine-tooth saw; maintain close joints to avoid thermal bypass.
• Seal or tape as specified: Ensures continuity with air and vapour control layers.
• Fix securely: Mechanical fixings, adhesives, or retention by framing depending on application.
• Protect on site: Store boards flat, dry, and covered until required.
  
  

Compliance & Performance

• Thermal conductivity: 0.022 W/m·K (BS EN 12667).
• Compressive strength: ≥140 kPa (BS EN 826).
• Reaction to fire: Euroclass E (BS EN 13501-1).
• Environmental performance: Zero ODP, low GWP, BRE Green Guide Rating A.
• Part L Regulation compliance: High-thickness profile specifically designed to meet the stringent U-value requirements of Approved Document L for new build dwellings and existing extensions.
• Fabric energy efficiency: Supports a "fabric first" approach by providing a continuous thermal layer that reduces carbon emissions and improves the overall SAP rating of the build.
• Important note: This product must be installed with tightly abutted joints and high-quality foil tape sealing to ensure the continuity of the thermal barrier and maintain compliance with building regulations.