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Celotex PIR insulation is one of the most versatile and widely used insulation materials in the UK construction industry. Known for its excellent thermal performance, lightweight boards, and multi-purpose suitability, Celotex remains a go-to choice for new builds, renovations, extensions, and retrofit upgrades. If you’re planning a project and looking to maximise efficiency, reduce heat loss and stay compliant with Building Regulations, exploring the full range of Celotex PIR insulation boards is a smart place to start.
PIR (polyisocyanurate) insulation is valued for its low thermal conductivity — typically around 0.022 W/m·K. This makes Celotex boards far more efficient per millimetre than many mineral wool or EPS alternatives, allowing you to achieve target U-values without dramatically increasing wall, roof, or floor build-ups.
Celotex boards are also:
The roof is where most heat is lost in a typical home, so using high-performance insulation makes a dramatic difference. Celotex PIR boards are widely used in both pitched and flat roof constructions.
Celotex between and over rafters is a popular configuration because PIR achieves high U-values without requiring deep rafters or excessive boarding. Typical uses include:
For warm-deck flat roofs, Celotex is often specified due to its strength and stability. It can be installed above the deck beneath waterproofing membranes, helping to create a continuous, moisture-resistant thermal layer.
Celotex PIR insulation supports multiple wall construction methods for both new builds and retrofits.
Although dedicated full-fill cavity boards exist, Celotex PIR is often used for partial-fill cavity systems where high performance per mm is needed. Partial fill also maintains an air gap, supporting effective moisture drainage.
Celotex insulated plasterboard is commonly used for dry lining upgrades. Ideal for:
PIR boards provide reliable performance between studs or as an external sheathing layer. The foil facings help manage moisture movement, contributing to a healthier, longer-lasting structure.
Floor insulation is essential for energy efficiency, underfloor heating performance, and compliance with Part L. Celotex PIR boards are commonly used in:
The high compressive strength of Celotex boards ensures durability under load, preventing long-term sagging or performance loss.
Builders favour Celotex in renovation projects because it offers a high-performance solution without taking up excessive space — crucial for loft rooms, dormers and narrow wall cavities.
Celotex isn’t limited to domestic builds. High thermal performance, consistent manufacturing and certified approvals make PIR boards suitable for:
The wide product selection means each Celotex board is designed with a specific purpose in mind. Whether you’re insulating a roof, wall or floor, you’ll find a suitable size and thickness within the Celotex insulation range.
If your priority is the best performance per millimetre, PIR remains one of the strongest choices — combining efficiency, practicality and long-term stability in one lightweight package.
Notes: Always check official Celotex datasheets for thermal performance details, installation guidance and regulatory compliance for your specific project. Installation quality has a direct impact on real-world performance.
