CPD 06 2023: Introducing BS 5422 on pipework insulation

This CPD module, sponsored by Rockwool, looks at the latest version of BS 5422, the British Standard for thermal insulation of pipework and equipment, exploring recommendations and key updates for 2023

Insulation for HVAC and building services can offer more than just thermal benefits

The British Standards Institution (BSI) has published the latest version of BS 5422, the standard that forms the foundation of UK thermal insulation standards for building services. Originally published in 1977, BS 5422 was titled “Specification for the use of thermal insulating materials” and offered guidance on insulating metallic surfaces in domestic and industrial applications.

First updated in 1990, the title of BS 5422 was changed to “Methods for specifying thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within the temperature range -40°C to +700°C.”

Originally concerned with specifying insulation thicknesses based on economic payback, subsequent revisions (in 2001 and 2009) saw CO2 emissions become an important factor. The latest version of BS 5422, which will be explored in this module, has been long awaited by the industry.


  • Knowledge of BS 5422 and its scope of application
  • Awareness of key updates included in the latest version
  • Understanding of insulation guidance and how material choice affects the potential for fire spread

Standard introduction

Thermal insulation of pipework and equipment is one of the most cost-effective ways of conserving energy in both cooled and heated systems. The standard aims to help manufacturers ensure their products meet performance requirements, as well as help specifiers identify the minimum performance requirements for each application – improving the efficiency with which materials are used and increasing confidence within the industry that pipework and related equipment is achieving optimal performance.

Energy conservation has two considerations: cost saving + CO2 emissions reduction. Although any insulation measure has desired effects in both of these areas simultaneously, the extent of insulation that can be justified varies with the comparative costs of energy on the one hand, and alternative costs of carbon dioxide emission abatement on the other.

The standard contains specific guidance for the thermal insulation of pipework, ductwork and equipment, specifically exploring ways to:

  • Conserve energy for cooled and heated systems
  • Control condensation on cold surfaces
  • Control process or service temperatures
  • Slow freezing of contents
  • Protect personnel from extremes of surface temperature
  • Limit effects of systems on indoor building temperature.

BS 5422 can be adopted by specifiers and manufacturers of insulation materials including finishing materials, designers of insulation, and contractors working with thermal insulation. It is important to note that the standard does not apply to pipelines that are embedded underground, nor does it refer to the insulation of building construction.

BS 5422 is referenced in and can be used to comply with the following guidance:

  • Northern Ireland: Technical Booklet F
  • Ireland: Technical Guidance Document L
  • Scotland: Technical Handbook Section 6
  • England: Approved Document L
  • Wales: Approved Document L.
Often unseen, building services and HVAC systems support indoor comfort and environmental control

Updates for 2023

The 2023 update to BS 5422 has included a full revision of the standard and introduced a number of principal changes which reflect evolving energy efficiency standards.

Tables have been revised with simplification in mind. For example, higher thermal conductivity values for materials no longer supplied or very rarely used have been removed. Thermal conductivity values in this version are based on the most commonly used insulation materials at the time of revision.

All pipe sizes are indicated as “less than or equal to” values, which reduces the need for interpolation and tends to increase the overall thermal efficiency of targeted systems.

Reaction to fire is defined within the publication in terms of Euroclass, which is on par with what is currently used in Building Regulations documents (the default in product marking). Euroclass reaction to fire gives a more comprehensive and clear definition of the behaviour of materials exposed to fire than the more limited legacy BS 476-based scope.

Enhanced insulation thicknesses have been captured from the capital allowances in the legacy Energy Technology List (the government’s list for energy-efficient materials), and district heating tables for secondary and tertiary systems have been added. Plastic pipes (single wall) are treated as having no insulating value of their own.

The decision has been made to retain calculation methods on BS EN ISO 12241:2008, which have been superseded by those in BS EN ISO 12241:2022. An updated calculation tool is forecast for later in 2023; the drafting panel agreed to minimise delays by publishing this British Standard and placing recalculations on hold for a later update.

Insulation guidance

Considerations for the specification of insulation include the following:

Insulating building services improves energy efficiency and reduces heat losses and gains
  • Thermal conductivity: A material is given a number to describe how readily it transmits heat. Lower thermal conductivity indicates a more efficient thermal performance. It is crucial to consider long-term thermal performance and the impact that any degradation over time could have on system performance and costs. BS 5422: 2023 states that “additional allowances shall be made to confirm that the specified performance is achieved where system inefficiencies are created through the ageing of the product”. According to testing completed at the Danish Technical Institute in 2023, stone wool insulation has proven to retain its thermal properties for over 65 years.
  • Thermal bridges: The correct detailing of thermal bridges is paramount to achieving the full benefits of insulating building services. According to BS 5422: 2023, “to limit heat transfer through supports, load-bearing insulating material should be used on the pipe or vessel between the support and the surface to be insulated”.
  • Surface emissivity: The ratio of the energy radiated from a material’s surface is referred to as surface emissivity. It is a dimensionless number ranging from 0 to 1. The emissivity will depend on the surface: a clean and polished metal will have a lower emissivity, whereas a rough metal surface will have a higher emissivity.
  • Service temperature: Maximum service temperature is the highest temperature to which the thermal insulation of a material may be exposed without significant changes in properties – so it can continue to function within the specified limits of its performance. The service temperature rating of the chosen insulation product should conform with its intended application.
  • Noise and vibration: While outside the scope of BS 5422, specifiers should be aware that insulation material choice can impact the level of noise and vibration arising from building services and heating, ventilation and air conditioning (HVAC) systems.

Reaction to fire

Specifiers should be aware of how material choice can impact the potential for fire spread. The reaction to fire of insulation products is classified through BS EN 13501-1, which considers results from the following tests:

  • Ignitability
  • Rate of flame spread across the surface
  • Amount of heat released during combustion
  • Rate and level of smoke release
  • Character changes, such as the release of flaming droplets.

Results are assessed and products are assigned a rating from A1 (best) to F (worst). With the exception of A1, ratings are appended with “s” and “d” to indicate emitted levels of smoke and flaming droplets.

Between 2019 and 2022, “gas or smoke” was listed as the cause of just over half of all fire fatalities in the UK. Smoke consists of particles, vapours and toxic gases, all of which can be harmful to human health. According to BS 5422: 2023, “In the event of a fire some insulation systems can generate appreciable quantities of smoke and toxic fumes. Consideration should be given to the choice of materials bearing in mind their location, eg enclosed areas or adjacent to air ducts through which the smoke or fumes may spread.”

It must also be ensured that the fire resistance of compartment walls and floors is not compromised when penetrated by building services and HVAC systems. The standard states that “insulation systems on pipework or ductwork traversing a fire resisting division shall maintain the level of fire resistance of the wall, floor or cavity barrier through which they pass.”

Non-combustible materials should be used wherever possible, particularly in the building envelope of all high risk buildings, including all buildings taller than 11m, those having more than three storeys, or vulnerable occupancy buildings of any height.

Designers need to take the right approach to fire safety and should always go above and beyond minimum requirements.

An insulated pipe featuring pipe supports

Thickness calculations

Since thermal insulation of pipework and equipment represents one of the most cost-effective ways available of limiting carbon dioxide emissions, this standard highlights a series of thicknesses within its core tables, which have been calculated in accordance with environmental principles outlined in the document.

A specification produced in accordance with BS 5422 shall specify only those elements of the standard to which conformity is required for a specific application. The specification shall state the prime purpose of the insulation and shall specify the performance requirements for the selected insulation system. The specification shall identify the minimum performance requirements for each application or parameter. The application or parameter that requires the greatest thickness of insulation shall take precedence.

The performance requirements shall be specified in accordance with the appropriate clauses and tables of this standard, which shall be determined from the following factors:

  • System operating temperature
  • Design ambient air temperature
  • Relative humidity of the ambient air
  • Air velocity
  • Location of the plant (indoors or outdoors)
  • Pipe diameter (or flat surface dimensions)
  • Orientation of pipes (horizontal or vertical)
  • Vertical dimensions of flat surfaces
  • Emissivity of the outer surface.
Correct installation is essential to meet as-designed performance

For refrigerated, chilled and other cold applications, where applicable, water vapour permeance or resistance of the complete insulation system (including water vapour barrier, where applied) shall also be specified in accordance with the appropriate clauses and tables of this standard.

Insulation thicknesses are given for a range of thermal conductivities appropriate to the usual materials used for the application; thicknesses for intermediate thermal conductivities and pipe sizes may be deduced by calculation or interpolation. For guidance in selecting appropriate types of insulation and suitable methods of application, reference should be made to BS 5970.

Effective insulation improves the thermal performance of hot and cold pipework

The latest version of BS 5422 took effect on 30 June 2023, at which point the 2009 version was withdrawn. Regulatory guidance refers to BS 5422 dynamically. This means that BS 5422:2023 will apply to new projects, including those for which planning permission has been achieved, but where tender documentation has already been issued to potential installers or a contract has been awarded, BS 5422:2009 continues to apply.

BS 5422 is not a prescriptive document and recognises that there are many reasons why the insulation of pipes, tanks, vessels, ductwork and equipment may be required. It is therefore important that specifiers state the criteria or specific clause or reference in this standard in any specification.

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