Celotex Insulation: Complete Product Range, Specifications, and Selection Guide

Celotex insulation is a PIR (polyisocyanurate) foam insulation board manufactured by Saint-Gobain, available across multiple product ranges designed for specific building applications. The Celotex range includes GA4000 (general application), TB4000 (thin boards), XR4000 (roofing), and FL4000 (floors) among others, with thicknesses from 25mm to 200mm and a typical thermal conductivity of 0.022 W/mK. Trade professionals in the UK construction industry use Celotex as one of the most widely stocked PIR brands, with availability through most builders merchants and insulation specialists.

About Celotex PIR Insulation

Celotex is manufactured by Saint-Gobain at their facility in South Wales. The brand has been present in UK construction for decades, becoming one of the most recognised names in rigid insulation. In common usage, “Celotex” often gets used generically to refer to any PIR board, similar to how “Hoover” became synonymous with vacuum cleaners – though technically Celotex is a specific brand within the PIR market.

What makes Celotex insulation?

Celotex boards consist of a rigid PIR foam core with facings bonded to both sides. Most products use aluminium foil facings, though some specialist ranges use glass tissue or other facing materials. The PIR foam forms through a chemical reaction creating a closed-cell structure where individual cells are sealed, trapping low-conductivity gas that provides thermal insulation.

The manufacturing process produces boards with consistent density (30-35 kg/m³) and thermal performance (0.022 W/mK lambda value for most products). This consistency matters for reliable U-value calculations – you can specify 100mm Celotex and confidently predict the thermal performance without variation between batches.

Celotex vs Other PIR Brands

From a technical performance standpoint, Celotex performs identically to other major PIR brands like Kingspan, Recticel, or Ecotherm. All meet BS EN 13165, achieve 0.022 W/mK lambda values, and provide similar compressive strength at equivalent grades.

The practical differences come down to:

• Availability: Celotex has very high distribution coverage. Most builders merchants stock Celotex, making it easy to source
• Product range: Celotex offers specialist products for specific applications, though Kingspan has a wider overall range
• Pricing: Varies by region and supplier. Celotex pricing sits in the middle – not the cheapest, not the most expensive
• Technical support: Saint-Gobain provides technical datasheets, U-value calculators, and specification guidance

For most applications, choosing Celotex over Kingspan or vice versa makes minimal practical difference. The decision often comes down to what your regular merchant stocks or which brand gives better trade pricing on bulk orders.

Celotex Product Range Overview

Celotex segments its product range by application. Each series is designed for specific uses with appropriate facings, compressive strength, and certifications.

Main Product Series

The series designation helps identify appropriate products for your application, though there’s overlap. GA4000 works for floors, walls, and roofs. TB4000 suits walls and some roof applications but not floors due to lower compressive strength. Understanding which series fits your needs prevents specification errors.

Lambda Values Across the Range

Most Celotex products declare 0.022 W/mK thermal conductivity. A few specialist products vary:

• GA4000, XR4000, CW4000, FL4000: 0.022 W/mK
• TB4000: 0.022 W/mK
• Some ultra-thin products: 0.023 W/mK

These lambda values represent aged performance after cell gas stabilisation. Fresh boards might perform slightly better, but calculations use the declared aged value to ensure real-world performance matches design.

Celotex GA4000 Series: General Application Boards

The GA4000 series represents Celotex’s most versatile product line. “GA” stands for general application – these boards work across roofs, walls, and floors without application-specific limitations.

GA4000 Specifications

• Lambda value: 0.022 W/mK
• Board size: 2400mm x 1200mm (2.88m² per board)
• Compressive strength: 120 kPa minimum
• Facings: Aluminium foil both sides
• Fire classification: Class E
• Operating temperature: -50°C to +80°C
• Water vapour resistivity: 150 MNs/gm

Where GA4000 Works

The 120 kPa compressive strength makes GA4000 suitable for residential and light commercial floor applications. This strength handles screed weight, floor finishes, furniture, and foot traffic without compression. For reference, 120 kPa equals 12 tonnes per square metre.

For walls, the compressive strength exceeds requirements since walls don’t load the insulation. GA4000 works in cavity walls (partial fill), internal wall insulation, and external wall insulation systems.

For roofs, GA4000 handles pitched roof applications (between rafters, above rafters, or below rafters) and flat roof warm deck constructions. The foil facings suit most waterproofing systems, though torch-applied felts require boards with glass tissue facings instead.

GA4000 Thickness Options

Available thicknesses: 25mm, 30mm, 40mm, 50mm, 60mm, 70mm, 75mm, 80mm, 90mm, 100mm, 110mm, 120mm, 130mm, 140mm, 150mm, 160mm, 170mm, 180mm, 190mm, 200mm

The wide thickness range means you can specify exactly what’s needed for target U-values without over-specifying. A floor achieving 0.18 W/m²K needs 100mm. A floor achieving 0.15 W/m²K needs 120mm. You’re not forced to jump from 100mm to 150mm with nothing in between.

Common GA4000 Applications

Solid floors: 100mm Celotex GA4000 above damp-proof membrane beneath screed achieves 0.17-0.18 W/m²K for Part L compliance. The boards lay loose with taped joints, then minimum 65mm screed over the top.

Cavity walls: 75-100mm GA4000 in partial fill cavity wall construction achieves 0.16-0.20 W/m²K depending on complete build-up. Boards fix against inner leaf blockwork with minimum 50mm residual cavity to outer brick leaf.

Pitched roofs: 100mm GA4000 friction-fit between rafters achieves 0.19-0.21 W/m²K. For lower U-values, combine 100mm between rafters with 50-75mm over rafters to achieve 0.15 W/m²K or better.

Flat roofs: 120-150mm GA4000 above structural deck beneath waterproofing membrane achieves 0.15-0.18 W/m²K for warm flat roof construction. Vapour control layer sits beneath insulation.

Celotex TB4000 Series: Specifications and Uses

The TB4000 series covers thin board applications where space constraints limit insulation thickness. “TB” stands for thin board – these products suit retrofit situations or applications where every millimetre of build-up depth matters.

TB4000 Specifications

• Lambda value: 0.022 W/mK
• Board size: 2400mm x 1200mm
• Compressive strength: 100 kPa minimum (lower than GA4000)
• Facings: Aluminium foil both sides
• Fire classification: Class E
• Available thicknesses: 20mm, 25mm, 30mm, 40mm, 50mm, 60mm, 75mm

Where TB4000 Works (and Doesn’t)

The lower compressive strength (100 kPa vs 120 kPa for GA4000) means TB4000 isn’t suitable for floor applications beneath screed. The boards would compress under loading, reducing thermal performance and potentially causing screed cracking.

TB4000 works for:

Internal wall insulation: Where room size constraints limit insulation thickness, 50-75mm TB4000 provides maximum thermal performance in minimal depth. Combined with plasterboard and battens, a 75mm TB4000 system adds approximately 90-100mm to wall thickness.

Roof void conversions: When converting loft space to habitable rooms, ceiling height often becomes critical. Using thinner insulation (even if it means slightly higher U-values) preserves headroom. 75mm TB4000 between rafters plus 50mm over rafters achieves reasonable thermal performance while maintaining usable ceiling height.

Retrofits with height constraints: Victorian properties with low existing ceiling heights can’t accommodate thick floor insulation without creating steps at doorways. 50-75mm TB4000 provides partial thermal improvement within tight constraints.

When to Use GA4000 Instead

If space allows, GA4000 is the better choice. The higher compressive strength gives more application flexibility, and the wider thickness range (up to 200mm) provides more options. TB4000 is for situations where space constraints force compromises.

Celotex for Roofs: XR, TB, and Crown-Fix Ranges

Celotex produces several roofing-specific product ranges, each designed for particular roof applications.

XR4000 Series (Pitched Roofs)

The XR4000 range suits pitched roof applications with features specific to rafter installation:

• Shiplap edges on longer edges for tighter joints between boards
• Foil facings suitable for most breathable membranes
• Available in thicknesses commonly used in pitched roofs: 50mm, 75mm, 100mm, 120mm, 140mm, 150mm

The shiplap edge creates a tongue-and-groove type joint that reduces air gaps between boards. For between-rafter installations, this improves airtightness. For above-rafter installations, it reduces cold bridging at joints.

XR4000 specifications match GA4000 (0.022 W/mK lambda, 120 kPa compressive strength), so from a thermal and structural standpoint they’re identical. The shiplap edge is the main differentiator.

Does the shiplap edge matter? For between-rafter installations with properly taped joints, the performance difference between XR4000 and GA4000 is minimal. Both work fine. For above-rafter installations without taping (relying on counter battens to compress boards together), shiplap edges provide slightly better airtightness.

TB4000 for Roofs

The standard TB4000 range (covered earlier) works for pitched roofs where thinner insulation is acceptable. The main limitation is the thickness range stops at 75mm, which often isn’t enough to meet current Part L requirements without additional insulation layers.

RS4000 Series (Roof Sarking)

RS4000 products are designed for warm pitched roof installations above rafters (sarking boards):

• Available in thicknesses: 100mm, 120mm, 140mm
• Foil facings on both sides
• Suitable for counter batten fixing before roof covering installation

These products are essentially GA4000 boards marketed specifically for sarking applications. The technical specifications match GA4000, so you could use GA4000 for sarking if that’s what your merchant stocks.

Crown-Fix Range

Crown-Fix products have glass tissue facings instead of aluminium foil. This facing withstands torch-applied roofing felt installation where heat would damage foil facings:

• Available thicknesses: typically 80mm-150mm
• Glass tissue facings suitable for torch-on felt application
• Slightly lower vapour resistance than foil-faced boards

For flat roof installations using torch-applied three-layer felt systems, Crown-Fix or similar glass-tissue-faced boards are required. For single-ply membranes or liquid-applied systems, standard foil-faced boards work fine.

Celotex for Floors: GA and FL Ranges

Floor applications require adequate compressive strength to prevent insulation compression under loading. Celotex offers two main options.

GA4000 for Floors

Standard GA4000 boards with 120 kPa compressive strength suit most residential and light commercial floor applications:

• Suitable beneath sand-cement screed (minimum 65mm thick)
• Adequate for standard domestic loading
• Works with underfloor heating systems
• Available in all thicknesses from 25mm to 200mm

For a typical solid floor construction, 100mm GA4000 achieves 0.17-0.18 W/m²K when installed above concrete slab and damp-proof membrane beneath screed. This comfortably meets Part L requirements for ground floors (0.18 W/m²K maximum).

The installation sequence:

1. Concrete ground-bearing slab
2. Damp-proof membrane (lapping with wall DPC)
3. 100mm GA4000 boards with taped joints
4. Perimeter edge insulation strip
5. Minimum 65mm unbonded screed
6. Floor finish

FL4000 for Enhanced Strength

The FL4000 range offers enhanced compressive strength for applications with higher loading requirements:

• Compressive strength: 150 kPa minimum (vs 120 kPa for GA4000)
• Suitable for commercial applications
• Available thicknesses: typically 75mm-150mm
• Same 0.022 W/mK lambda value as GA4000

When to specify FL4000 instead of GA4000:

Commercial kitchens: Heavy equipment loading and frequent traffic Plant rooms: Equipment weight and maintenance access loading Retail spaces: Higher occupancy densities and merchandise display loading Warehouse conversions: Where loading exceeds standard residential patterns

For standard residential applications, GA4000 provides adequate strength. FL4000 costs more, and that extra cost provides no benefit unless you actually need the higher compressive strength.

Suspended Timber Floors

For suspended timber floors, boards install between joists (supported on battens) rather than carrying floor loading directly. In this application, compressive strength becomes irrelevant since boards hang between joists without loading. Standard GA4000 works fine.

The limiting factor becomes joist depth. 100mm insulation requires minimum 150mm joist depth to accommodate insulation plus support battens and airspace. Shallower joists need thinner insulation or above-joist installation methods.

Celotex Thickness Options: 25mm to 150mm

Celotex manufactures boards from 20mm to 200mm thickness, though availability varies by product range and supplier stock. Understanding which thicknesses work for common applications helps specification.

Common Thickness Applications

25mm Celotex:

• Internal wall insulation where space is severely limited
• Supplementary insulation layer over existing insulation
• Thin wall applications in retrofit situations
• U-value achieved in solid floor: approximately 0.55 W/m²K (inadequate for Part L compliance as sole insulation)

50mm Celotex:

• Cavity wall insulation in narrow cavities
• Internal wall insulation in space-constrained retrofits
• Supplementary roof insulation below rafters
• U-value achieved in solid floor: approximately 0.32 W/m²K

75mm Celotex:

• Cavity wall insulation
• Internal wall insulation
• Some floor applications in mild climate zones
• U-value achieved in solid floor: approximately 0.23 W/m²K

100mm Celotex:

• Most common thickness for Part L compliance across multiple applications
• Solid floors achieving 0.17-0.18 W/m²K
• Cavity walls achieving 0.16-0.17 W/m²K
• Pitched roofs between rafters achieving 0.19-0.21 W/m²K
• 100mm is the workhorse thickness for meeting current Building Regulations

120mm Celotex:

• Flat roofs achieving 0.15-0.16 W/m²K
• High-performance floor applications
• Scotland Building Standards compliance
• U-value achieved in solid floor: approximately 0.15 W/m²K

150mm Celotex:

• High-performance applications
• Scotland pitched roof compliance
• Future-proofing against anticipated regulation tightening
• U-value achieved in solid floor: approximately 0.13 W/m²K

Selecting Thickness for Your Project

Work backwards from your target U-value. Part L 2021 requires:

• Floors: 0.18 W/m²K → 100mm typically achieves this
• Walls: 0.26 W/m²K → 50-100mm achieves this depending on construction
• Roofs: 0.16 W/m²K → 100-150mm achieves this depending on construction type

Scotland requires stricter U-values (floors 0.15 W/m²K, roofs 0.13 W/m²K), typically necessitating 120-150mm thicknesses.

Beyond regulatory compliance, consider:

Future-proofing: Building Regulations will continue tightening. Specifying slightly beyond minimum requirements (for example, 0.15 W/m²K for floors instead of 0.18 W/m²K) adds minimal cost now but extends compliance lifetime.

Energy performance certificates: Lower U-values improve EPC ratings, which affects property value and rental potential. The difference between 100mm and 120mm insulation might move a property from EPC band D to C.

Running costs: Better insulation reduces heating costs. For a typical 50m² ground floor, improving U-value from 0.18 W/m²K to 0.15 W/m²K saves approximately 200 kWh annually. Over 30 years, this adds up significantly.

Selecting the Right Celotex Product

Choosing the correct Celotex product depends on application, performance requirements, and practical constraints.

Decision Framework

Step 1: Identify Application

• Floor beneath screed → GA4000 or FL4000
• Floor between joists → GA4000 or XR4000
• Cavity wall → GA4000 or CW4000
• Internal wall insulation → GA4000 or TB4000 depending on space constraints
• Pitched roof between rafters → GA4000 or XR4000
• Pitched roof above rafters → GA4000 or RS4000
• Flat roof → GA4000 or Crown-Fix depending on waterproofing system

Step 2: Calculate Required Thickness Use U-value calculation tools or tables to determine thickness needed for target U-value. Part L maximum U-values provide the baseline, but consider specifying lower U-values for future-proofing.

Step 3: Check Compressive Strength Requirements

• Floors beneath screed: minimum 120 kPa (GA4000 or FL4000)
• Floors with enhanced loading: 150 kPa (FL4000)
• Walls and roofs: 100-120 kPa adequate (any range)

Step 4: Verify Facing Compatibility

• Torch-applied felt systems: require glass tissue facings (Crown-Fix)
• Most other systems: standard foil facings work (GA4000, XR4000, etc.)

Step 5: Confirm Availability Not all thicknesses of all ranges stock at all merchants. Check availability before finalising specification. If your chosen product isn’t readily available, an equivalent from the GA4000 range usually works as an alternative.

Common Specification Mistakes to Avoid

Using TB4000 for floors: The lower compressive strength (100 kPa) causes compression under loading. Always use GA4000 minimum (120 kPa) for floors beneath screed.

Specifying thickness without U-value calculation: Don’t assume 100mm achieves Part L compliance for all applications. Run proper U-value calculations for your specific build-up.

Ignoring thermal bridging: Edge details, wall ties, and junctions add to calculated U-values. Account for thermal bridging in your design U-value, not just centre-of-panel performance.

Over-specifying product range: GA4000 works for most applications. Don’t specify FL4000 for standard residential floors or RS4000 for standard pitched roofs unless you have specific requirements. The extra cost provides no benefit.

Foil facings with torch-applied felt: Using standard foil-faced boards with torch-applied felt melts the facings. Specify Crown-Fix or equivalent glass tissue faced products for torch-on felt systems.

Celotex Technical Data and Certifications

Understanding technical certifications and product standards helps specification and Building Control approval.

British and European Standards

All Celotex PIR products manufactured to:

• BS EN 13165:2012+A2:2016 – Thermal insulation products for buildings. Factory made rigid polyurethane foam (PUR) and polyisocyanurate foam (PIR) products. Specification.

This standard sets requirements for dimensional stability, compressive strength, thermal resistance, reaction to fire, and other characteristics. Products meeting BS EN 13165 demonstrate consistent, reliable performance.

CE Marking

Celotex products carry CE marking demonstrating compliance with Construction Products Regulation. The CE mark confirms products meet declared performance characteristics and have undergone appropriate testing and factory production control.

Declared Performance

For each product, Celotex publishes Declarations of Performance (DoP) specifying:

• Thermal conductivity (lambda value)
• Thermal resistance (R-value) for each thickness
• Reaction to fire classification
• Compressive strength
• Water absorption
• Dimensional stability

These declarations provide the data needed for U-value calculations and Building Regulations compliance demonstrations.

BBA Certification

Many Celotex products hold British Board of Agrément (BBA) certificates. These independent certifications assess products for fitness for purpose, durability, and compliance with Building Regulations. BBA certificates provide third-party verification of manufacturer claims.

Fire Classification

Celotex PIR boards typically achieve:

• Class E reaction to fire rating per BS EN 13501-1

This classification suits most residential and commercial applications when used as part of complete constructions. For buildings over 18m (approximately 6 storeys), additional fire safety considerations apply following post-Grenfell regulations. Check current Building Regulations guidance for high-rise applications.

Testing and Quality Control

Saint-Gobain maintains factory production control systems ensuring consistent product quality:

• Regular sampling and testing of finished boards
• Monitoring of foam density, thermal conductivity, and compressive strength
• Dimensional checks ensuring thickness and size tolerances
• Facing bond strength testing

This quality control system explains why PIR insulation from major manufacturers like Celotex provides consistent, predictable performance across batches and over time.

Environmental Product Declarations

Celotex publishes Environmental Product Declarations (EPD) quantifying environmental impacts of their products. These declarations help projects pursuing BREEAM ratings or other environmental assessment schemes.

Warranty and Technical Support

Saint-Gobain provides technical support for Celotex specification:

• U-value calculation services
• Construction detail drawings
• System compatibility guidance
• CPD presentations for design teams

Product warranties typically come through installation system warranties (for example, flat roof system warranties) rather than insulation-specific warranties. When insulation forms part of a certified system, ensure all components meet system requirements.

Using Technical Data in Practice

For Building Control submissions, provide:

• Product Declaration of Performance showing thermal conductivity
• U-value calculations using declared lambda values
• Construction details showing installation method
• Fire classification evidence where required

Building Control officers need to verify proposed constructions meet Part L requirements. Complete technical documentation speeds approval and prevents queries during construction. Need reliable Celotex insulation for your project? Online Insulation stocks the complete Celotex range across all thicknesses, with fast UK delivery for trade professionals.