BS 5422 Pipe Insulation Standards Guide For Pipe Insulation UK

BS 5422:2023 is the British Standard code of practice for specifying thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within its stated temperature range. For pipework, it provides criteria and tables used to determine appropriate insulation performance and thickness for different services and operating conditions.

Required thickness depends on the service type, pipe outside diameter (OD), operating temperature, insulation thermal conductivity, surface emissivity, heat-loss criterion or condensation-control requirement, and other prescribed conditions. The tables below are based on current manufacturer-published BS 5422:2023 guidance for specific insulation products. They are not universal — different insulation materials achieve compliance at different wall thicknesses. Always verify against the current BS 5422:2023 standard and the relevant manufacturer's technical data for your specific application.

For the LTHW application shown below, the manufacturer guidance provides Table 15A and Table 15B thicknesses:

• Table 15A — base level insulation thickness
• Table 15B — enhanced level insulation thickness

The applicable level for your project will be determined by the relevant Building Regulation, project specification or contract requirement. The thicknesses shown in the tables below assume a low-emissivity surface finish (ε ≈ 0.05). Consult the manufacturer's BS 5422:2023 technical bulletin for other surface conditions.

BS 5422:2023 Pipe Insulation Thickness Tables

Table 1 — Heating Pipework LTHW ≤95°C — Kingspan Kooltherm Pipe Insulation

Source: Kingspan Kooltherm Pipe BS 5422:2023 Technical Bulletin (current edition). Low-emissivity surface (ε ≈ 0.05), LTHW service ≤95°C, heated internal space. Verify against current Kingspan technical data before specifying.

Source: Kingspan Kooltherm Pipe BS 5422:2023 Technical Bulletin. Low-emissivity surface (ε ≈ 0.05), LTHW service ≤95°C, heated internal space. Verify against current Kingspan technical data before specifying.

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Table 2 — Heating Pipework LTHW ≤95°C — ROCKWOOL RockLap H&V

Source: ROCKWOOL BS 5422:2023 Guide (current edition). RockLap is a non-combustible mineral wool pipe section that provides a non-combustible insulation option where the specification requires appropriate reaction-to-fire performance. Its higher thermal conductivity compared to phenolic foam means greater wall thicknesses are required to achieve the same BS 5422 performance level. Low-emissivity surface (ε ≈ 0.05), LTHW service ≤95°C, heated internal space. Verify against current ROCKWOOL technical data before specifying.

Source: ROCKWOOL BS 5422:2023 Guide. Low-emissivity surface (ε ≈ 0.05), LTHW service ≤95°C, heated internal space. For 60mm and 70mm requirements, contact our technical team to confirm available product and multi-layer options. Verify against current ROCKWOOL technical data before specifying.

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How to Identify the Correct OD Band

BS 5422 thickness tables are indexed by pipe outside diameter (OD) band, not by nominal pipe size. Always use the actual measured OD of the pipe to identify the correct band. For common UK copper tube sizes: 15mm copper has a 15mm OD (≤17.2mm band); 22mm copper has a 22mm OD (≤26.9mm band); 28mm copper has a 28mm OD (≤33.7mm band); 35mm copper has a 35mm OD (≤42.4mm band); 42mm copper has a 42mm OD (≤48.3mm band); 54mm copper has a 54mm OD (≤60.3mm band).

For steel, stainless steel or other pipe materials, refer to the relevant pipe standard for the declared outside diameter. See our Copper Pipe Sizes guide for further detail.

High-Temperature and Steam Pipework

BS 5422:2023 covers high-temperature services including MTHW, HTHW, steam and industrial process pipework, but required thickness varies significantly with operating temperature band, pipe OD and insulation material. A single generic table cannot safely represent these conditions across the full temperature range.

For high-temperature applications, use the manufacturer's current BS 5422:2023 product-specific tables for the relevant temperature band. ROCKWOOL provides separate BS 5422:2023 tables for different temperature bands in its current specification guide. Contact our technical team for product-selection guidance.

Chilled Water and Refrigeration Pipework

Condensation-control thickness for chilled water and refrigeration pipework cannot be determined from pipe OD and fluid temperature alone. Required thickness also depends on ambient temperature, relative humidity, surface emissivity, insulation thermal conductivity and the vapour-control performance of the insulation system. BS 5422:2023 addresses these services in specific clauses, tables and annexes.

ROCKWOOL's current condensation guidance, for example, is explicitly tied to stated design conditions (25°C ambient, 80% RH, ε = 0.05). Applying those values to a different ambient environment would give an incorrect result. For chilled water and refrigeration pipework, obtain the manufacturer's current product-specific condensation-control thickness data for your stated design conditions.

Refrigeration & chilled water pipe insulation | Condensation control guide | Contact our technical team

Key BS 5422:2023 Principles

• Performance-based — BS 5422:2023 specifies minimum thermal performance, not a single material. Different insulation materials achieve compliance at different wall thicknesses depending on their declared thermal conductivity.
• Thermal conductivity is product-specific — required thickness varies between insulation materials and products. Use the manufacturer's current BS 5422:2023 product-specific thickness tables rather than generic lambda comparisons.
• OD band, not nominal size — BS 5422 thickness tables are indexed by pipe outside diameter band. Always use the actual pipe OD to identify the correct band.
• Check the applicable table — the LTHW manufacturer guidance above provides Table 15A and Table 15B thicknesses. Other services and conditions use different BS 5422 tables and criteria.
• Location matters — pipes in unheated spaces (plant rooms, roof voids, external) may require thicker insulation than pipes in heated internal spaces. Consult the relevant BS 5422:2023 tables for your installation environment.
• Surface emissivity matters — thickness tables assume a stated surface emissivity. Painted, jacketed or high-emissivity surfaces require different thickness values from the same tables.

What if the Required Thickness Is Not a Standard Available Size?

BS 5422:2023 requirements are performance-based. A calculated or tabulated minimum thickness may not correspond to a standard stocked or manufactured thickness for the selected insulation system. For example, if a table or calculation indicates a minimum of around 38mm, that may not correspond to a standard manufactured wall thickness for the selected product.

Where the required minimum falls between available sizes, select a suitable available thickness that meets or exceeds the required performance, subject to BS 5422:2023, the product manufacturer's technical data and the project specification. In some cases a multi-layer insulation solution may be appropriate. Kingspan explicitly notes this principle in its BS 5422:2023 guidance.

If you are unsure which product and thickness to specify, contact our technical team.

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Related Guides

• What Thickness Pipe Insulation Do I Need?
• BS 5422 Pipe Insulation Thickness Guide
• How to Measure Pipe Insulation Size
• Copper Pipe Sizes Explained
• Part L Compliance for Pipe Insulation

Guidance on this page is intended to support product selection and does not reproduce or replace BS 5422:2023. For formal specification and compliance work, consult the current British Standard, applicable Building Regulations and manufacturer technical data.