100mm Celotex GA4100 PIR Insulation Board 2400mm x 1200mm

Product Overview

Foil-faced PIR insulation board, measuring 100mm in thickness for use in floors, walls, and roofs. 

Manufactured as part of the GA4000 range, it is intended for general application, meaning it can be confidently specified across a broad spectrum of build-ups without the need for specialist products.

The board consists of a rigid polyisocyanurate (PIR) core faced with low-emissivity foil on both sides. This construction provides excellent thermal resistance, helping to reduce heat loss through the building fabric while also acting as a vapour control layer. 

At 100mm thick, the most widely used thickness in the GA range, it is sized to fit most standard cavities and joist depths, making it straightforward to integrate into typical construction details.

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.
• GA4000 range (general application): Suitable for versatile use across 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 × 1200mm: Supplied in the industry-standard sheet size for insulation, ensuring compatibility across typical build-ups.
• Thickness 100mm: Popular and practical size for achieving strong thermal performance in standard build-ups.
  
  

Applications

• General insulation: Versatile board suitable for a wide range of domestic and commercial applications.
• Beam and block flooring: Maximum efficiency 100mm PIR boards are installed over the structural floor to provide a continuous thermal barrier beneath sand and cement or liquid screeds. 
• Concrete slab and oversite floors: High compressive strength enables boards to be laid directly over or under ground-bearing slabs to ensure the lowest possible U-values in new-build construction. 
• Suspended timber floors: Rigid boards are cut-to-fit and friction-supported between floor joists to significantly reduce heat loss through ventilated sub-floor voids. 
• Concrete slab overlays: Standard 100mm thickness allows for the upgrade of existing concrete floors to provide a thermal barrier equivalent to modern new-build specifications. 
• Underfloor heating systems: Reflective foil facers on both sides of the board enhance the efficiency of underfloor heating by reflecting heat upwards into the living space.
• Timber frame wall insulation: Maximum efficiency 100mm PIR boards are friction-fitted between timber studs to ensure the highest possible thermal ratings in wall assemblies. 
• Masonry wall dry-lining: Flagship 100mm boards are fixed to the internal face of solid or cavity masonry walls to provide a thermal barrier equivalent to modern new-build specifications. 
• Pitched roof insulation: Full-thickness 100mm boards are installed between or over rafters to create a high-specification, regulation-compliant thermal envelope. 
• Flat roof insulation: High compressive strength allows for installation beneath a waterproof membrane or over a structural deck to provide the ultimate thermal solution for the roof covering.
• Summerhouse and garden room insulation: High-performance 0.022 W/mK thermal conductivity provides maximum heat retention within timber stud walls and roof rafters.
• Conservatory warm-roof conversions: Optimum 100mm thickness enables roof structures to meet or exceed Part L U-value requirements during solid-roof upgrades.

Installation Guidance

• Measuring and cutting: Measure the aperture accurately and cut the board using a fine-toothed saw or sharp knife for a tight friction fit.
• Positioning and fixing: Place the board securely against the substrate or between structural members, ensuring no gaps are left between adjacent boards.
• Sealing joints: Apply high-quality aluminium foil tape to all board joints to maintain the integrity of the vapour control layer.
• Mechanical attachment: Use appropriate insulation fixings or adhesive as specified by the project requirements to secure boards to walls or ceilings.
• Fire lining (wall applications): Ensure the insulation used in wall applications is covered with a fire-rated lining, such as 12.5mm plasterboard, to meet safety requirements.

Compliance & Performance

• Thermal conductivity: Achieves a declared Lambda value of 0.022 W/mK in accordance with BS EN 13165.
• Compressive strength: Rated at ≥140 kPa when tested to BS EN 826, making it suitable for floor applications subject to light loads. 
• UK Building Regulations Part L: Helps meet Part L (Fuel and Power) requirements; however, 100mm may require additional layers to meet specific new-build U-value targets.
• UK Building Regulations Part B: Rated as Euroclass E in accordance with BS EN 13501-1; this material is combustible and must be installed behind a fire-rated lining in wall applications.
• UK Building Regulations Part C: Requires the use of a separate Vapour Control Layer (VCL) and taped joints in many applications to prevent interstitial condensation as per Part C (Site preparation and resistance to contaminants and moisture). 
• Environmental impact: Zero Ozone Depletion Potential (ODP) and low Global Warming Potential (GWP) during the manufacturing process.
• Important note: UK Building Regulations vary by project and location; always consult a Building Control Officer or Architect to confirm this thickness meets the legal U-value requirements for your specific build.

What Customers Are Saying

Customers consistently praise the Celotex GA4100 for its ease of cutting and fitting, particularly in summerhouse, loft conversion and extension projects. Several reviewers highlight how cleanly the boards slot between studs and rafters with minimal waste. Delivery speed and condition on arrival are frequently mentioned, with buyers noting boards arrived undamaged and on schedule. Trade professionals and DIYers alike rate the thermal performance highly, with multiple customers reporting noticeable improvements in room temperature. The competitive pricing compared to other PIR boards is a recurring positive, with several repeat buyers citing Materials Market as their preferred supplier.

Summarised by AI from customer reviews.