Celotex TB4000 PIR Insulation Board: A Complete UK Guide for Construction Professionals

Certified Applications in UK Building Projects

In the UK construction market, third-party certification is a critical indicator of a product's fitness for purpose. Celotex TB4000 has been assessed by the British Board of Agrément (BBA) for a range of specific applications. BBA certification provides assurance to specifiers, building control bodies, and warranty providers that the product, when installed correctly, can meet the requirements of the Building Regulations. This reliance on independent verification is a key feature of the UK industry, where assurance and risk management are paramount. A product without such certification for a given use would face significant barriers to market acceptance.  

BBA Certificate 17/5405 covers the use of Celotex TB4000 in the following applications :  

Floor Insulation:

• In solid concrete ground-bearing floors.  
• In suspended concrete beam and block floors. 
• Between the joists of suspended timber ground floors.  

Wall Insulation:

• As an internal insulation layer for solid masonry walls, a method commonly known as dry lining.  

• Within the structure of timber-framed and steel-framed wall systems, where it is typically installed between the vertical studs.  

Roof Insulation:

• In pitched roof constructions, where its thinner profile makes it well-suited as an insulation layer fixed below the rafters. This application is often used in combination with thicker insulation between the rafters to create a "warm roof" design and to effectively cut the thermal bridge created by the timber rafters themselves.  

• Within the build-up of warm flat roofs.  

Best Practices for Installation and Handling 

The designed thermal performance of Celotex TB4000 can only be achieved if the product is stored, handled, and installed correctly. The quality of workmanship on site is as important as the quality of the product itself. Poor installation practices, particularly the failure to ensure a continuous and gap-free insulation layer, can lead to thermal bridging and air leakage, which will significantly degrade the real-world performance of the building element.

On-Site Storage and Handling

To prevent damage and maintain performance, boards must be stored flat and raised off the ground to avoid contact with moisture. If stored outside, packs should be covered with an opaque, waterproof sheet to protect them from rain and prolonged exposure to sunlight. Care should be taken when handling the boards to avoid crushing or damaging the edges and corners; any significantly damaged boards should not be used.  

Cutting and Preparation

Boards can be cut to size using a fine-toothed saw or a sharp utility knife against a straight edge. During cutting, dust will be produced. It is essential to work in a well-ventilated area and wear appropriate personal protective equipment (PPE), including safety glasses, gloves to protect from the sharp foil edges, and a suitable dust mask to prevent inhalation of particles.  

Core Installation Principles

Regardless of the application, two principles are fundamental to a successful installation:

1. Continuity: The primary objective is to form an unbroken insulating envelope. To achieve this, all board joints must be tightly butted together. Gaps between boards create thermal bridges that allow heat to bypass the insulation.  

2. Sealing: To maximise thermal performance and create an effective air and vapour barrier, the joints between butted boards should be sealed with a suitable foil tape. This prevents air leakage and the passage of moisture.  

Application-Specific Guidance

• Floors: When installing over a concrete slab, a damp-proof membrane (DPM) must be laid first. Boards should be laid in a brick-bond pattern to stagger the joints and should be tightly butted. A perimeter upstand of insulation is critical at the junction with external walls to prevent a significant thermal bridge at the edge of the floor.  

• Timber Frame Walls: Boards should be cut to fit snugly between the vertical studs, ensuring they are pushed back against the external sheathing with no air gaps behind them. A separate vapour control layer (VCL) is typically required and is installed over the internal face of the studs before the plasterboard is fixed.  

• Pitched Roofs (Between Rafters): In a traditional "cold roof" design, it is vital to maintain a clear, ventilated air gap of at least 50mm between the top surface of the insulation and the underside of the roofing membrane or sarking felt. This ventilation path is necessary to allow moisture vapour to escape and prevent the risk of condensation forming within the roof structure.  

Compliance with UK Standards and Building Regulations

Celotex TB4000 is manufactured to meet established UK and European standards, and its primary purpose is to help building projects comply with the increasingly stringent energy efficiency requirements of the UK Building Regulations.

Manufacturing and Quality Standards

The product is manufactured in accordance with BS EN 13165, the harmonised standard for "Factory made rigid polyurethane foam (PU) products". This standard forms the basis for its UKCA marking, which demonstrates conformity with UK product safety requirements. The manufacturing facilities are certified to  

ISO 9001 for Quality Management and ISO 14001 for Environmental Management, indicating adherence to formalised systems for production consistency and environmental control. 

BRE Green Guide Rating of A.  

Part L of the Building Regulations 

In England, Approved Document L, Volume 1: Dwellings sets the standards for the conservation of fuel and power in residential buildings. A central requirement of this regulation is that building elements like walls, floors, and roofs must achieve specific target  

U-values. A U-value, measured in watts per square metre Kelvin (W/m2K), quantifies the rate of heat loss through a building element; a lower U-value signifies better thermal performance.  

Using high-performance insulation with a low thermal conductivity, such as Celotex TB4000, is a primary method for constructing building elements that meet the demanding U-value targets set by Part L. The table below summarises some of the key U-value targets for new domestic buildings and extensions in England.

Critical Use Limitation: The 11-Metre Rule

A crucial regulatory constraint applies to the use of Celotex TB4000. Following the Grenfell Tower fire and the subsequent inquiry, the UK Building Regulations were amended to improve the fire safety of external walls. These changes have had a direct impact on the specification of insulation products.

As a result of these amendments, Celotex TB4000, which has a Euroclass F reaction to fire classification, must not be used in the external walls of buildings that have a storey with a floor level 11 metres or more above ground level. The regulations for buildings of this height mandate the use of insulation products that are classified as non-combustible or of limited combustibility. This safety-driven requirement overrides the product's thermal performance characteristics in these specific applications and represents a fundamental division in the UK insulation market based on building height. It is the responsibility of the designer and specifier to ensure full compliance with this rule.  

Conclusion

Celotex TB4000 is a versatile and technically proficient PIR insulation board, engineered to help UK construction projects achieve high standards of energy efficiency. Its composite structure, combining a low-conductivity PIR foam core with low-emissivity foil facings, provides a dual-action approach to reducing heat loss through both conduction and radiation.

With a declared thermal conductivity of 0.022 W/mK and a wide range of BBA-certified applications for floors, walls, and roofs, the product is a valuable tool for meeting the U-value targets stipulated in Part L of the Building Regulations. However, its effectiveness is fundamentally linked to correct installation, where the continuity of the insulation layer and the sealing of joints are paramount to prevent thermal bridging and air leakage.

Specifiers and installers must also be acutely aware of the product's regulatory limitations. The Euroclass F fire classification means that Celotex TB4000 is legally prohibited from use in the external walls of buildings with a storey 11 metres or more in height. Adherence to this critical safety regulation is non-negotiable. When used within its certified applications and in compliance with all relevant standards, Celotex TB4000 provides a reliable solution for improving the thermal performance of buildings.

Legal Disclaimer

The information contained in this article is for general information purposes only. The information is provided based on publicly available technical data and regulatory documents at the time of writing. While we endeavour to keep the information up-to-date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, or suitability of the information for any particular purpose.

This content does not constitute professional design, engineering, or legal advice. It should not be used as a substitute for specific advice from a qualified professional and must not be relied upon for the specification of materials, the design of building elements, or the execution of construction work. Any reliance you place on such information is therefore strictly at your own risk.

Users should always consult the most current technical datasheets, Declarations of Performance, and BBA certificates directly from the manufacturer, and seek guidance from architects, structural engineers, or building control officers to ensure any proposed use complies with all applicable Building Regulations, standards, and legislation for their specific project. We shall not be liable for any loss or damage, including without limitation, indirect or consequential loss or damage, arising from the use of this information.