Standards relating to insulation: what is BS EN 13165, BS EN ISO 13788 and BS 5250:2021?

British and European standards relating to thermal insulation can be grouped into two approximate categories: those to do with the manufacture and testing of the insulation products themselves; and those relating to how products are used as part of wider building construction.

Standards documents are expensive to buy, and some run to hundreds of pages. With so many having a direct or indirect link to insulation manufacture and use, it can be hard to know which – if any – merit purchasing and reading. This blog post guide can help to point you in the right direction.

What is BS EN 13165?

BS EN 13165 is a European standard that sets out how to test and declare the technical specification of polyisocyanurate (PIR) insulation. It is one of a suite of standards that applies to the manufacture of different types of thermal insulation materials, and which ranges from BS EN 13162 to BS EN 13171.

At the time of writing, the current version is BS EN 13165:2013 + A2:2016, and its full title is Thermal insulation products for buildings. Factory made rigid polyurethane foam (PU) products. Specification. Extruded polystyrene (XPS) insulation is covered by its own standard, BS EN 13164.

All of these standards are what is known as a harmonised standard (hEN). The Construction Products Regulations (CPR) came into effect across EU member states in 2013 and included several ways by which products could be affixed with the CE mark. One route was harmonised standards.

CE marking is still relevant for the EU, while UKCA marking can be used in Great Britain under the UK Construction Products Regulations. As part of the process, manufacturers must issue a Declaration of Performance (DoP), which sets out the product’s performance.

“Harmonised standards are important because they set out an agreed method for assessing and testing products, and declaring their performance,” explains David Milner, Technical Team Leader at Celotex. “That means a product tested in one country can be compared to a product tested in another and can be specified with confidence in a different country to that of its manufacture.”

The hEN describes how testing should be carried out for mandatory and optional performance characteristics, and which standards to follow for that testing. It sets out no expectation in terms of products meeting a particular level of performance for any given characteristic.

Similarly, the hENs do not judge fitness for purpose. Being manufactured to a hEN doesn’t make an insulation product suitable for a particular application like a floor, wall or roof. That is where independent assessment and certification, like BBA certificates, come in.

Harmonised standards for insulation manufacture play a crucial part in ensuring the construction industry uses products whose performance has been properly tested and declared and can be relied upon consistently. Nevertheless, most readers don’t need to understand anything more about these standards than they exist in order for the CE mark to be applied, and that DoPs are a standardised method for presenting product performance data.

Click the link to view Celotex Declarations of Performance.

What is BS EN 13501-1?

Fire performance is one of the characteristics tested as part of the harmonised product standards described above. But because fire testing is such a prominent subject within the construction industry, it is worth touching on a standard that is regularly quoted when discussing product performance.

Like establishing a product’s length, width, thickness, thermal performance or compressive strength, reaction to fire performance is determined by specific test standards. BS EN 13501-1 is especially important because it uses the results of those tests to classify a product’s performance.

The full title of BS EN 13501-1:2018 is Fire classification of construction products and building elements. Classification using data from reaction to fire tests.

“BS EN 13501-1 is relevant to thermal insulation products, and gives us the well-known categories of A1, A2, B, C, D, E and F,” says David Milner. “However, it’s important to note this classification applies to the product in isolation, and not its use in a complete element build-up.”

For example, where a product is offered for use in flat roofs, the performance of the flat roof system can be tested. The roof’s external fire exposure performance is then classified to BS EN 13501-5:2016 Fire classification of construction products and building elements. Classification using data from external fire exposure to roofs tests.

What is BS EN ISO 6946?

Once a thermal insulation product has been selected for its particular combination of performance characteristics (often aided by it having a BBA certificate for the desired application), a specifier or installer needs to know what thickness to use to achieve the required thermal transmittance, or U-value – an essential aspect of meeting energy efficiency requirements in national building regulations.

There are two approaches for calculating U-values: a complex one, known as numerical modelling, and a simplified one, called the combined method.

The combined method is set out in the international standard BS EN ISO 6946:2017 Building components and building elements. Thermal resistance and thermal transmittance. Calculation methods.

The standard was first published in the late 1990s, and its method has been validated using numerical modelling. It calculates the thermal performance of each material layer within a build-up. Bridging materials (like repeating timber studs, joists or rafters) can be accounted for, as can certain repeating fixings (such as cavity wall ties).

Essential to note is that BS EN ISO 6946 cannot be used to calculate thermal bridging heat losses, whether linear thermal bridges at junctions or point thermal bridges such as fixing brackets. Achieving compliance with energy efficiency requirements relies on a combination of building element U-values and thermal bridging heat loss calculations.

When thermal insulation manufacturers offer a U-value calculation service – whether via their technical services team or an online calculator – they use the combined method. As David Milner explains:

“It is a reliable way to provide an accurate idea of the likely heat loss through a construction. It also includes ways to represent installation conditions, though good workmanship is still required on site in order for the stated U-value to be achieved.”

The combined method applies to floors, walls and roofs. For ground floor and basement U-value calculations specifically, the method set out in BS EN ISO 6946 has to be used in conjunction with further methods set out in BS EN 13370 (Thermal performance of buildings. Heat transfer via the ground. Calculation methods).

Click the link to view Celotex BBA certificates Insulation BBA Certificates | Celotex

Click the link to learn more about the Celotex online U-value calculator online U-value calculator

What is BS EN ISO 13788?

BS EN ISO 13788:2012 Hygrothermal performance of building components and building elements. Internal surface temperature to avoid critical surface humidity and interstitial condensation. Calculation methods is an international standard providing a simplified method of analysing interstitial condensation risk in building elements.

Within the construction industry, it is more commonly known as ‘the Glaser method’.

For most ‘typical’ forms of modern, vapour closed construction – including many masonry cavity wall and pitched roof constructions – the Glaser method is considered sufficient for assessing the risk of condensation.

It uses the layer-by-layer element approach employed by the combined method for U-value calculations. Temperature and humidity are predicted at the interface between each layer of the construction, assessing whether the quantity of moisture vapour present is likely to exceed the dew point temperature.

The method has its limitations, because moisture movement within buildings is highly complex and not yet fully understood. BS EN ISO 13788 even provides a list of assumptions that the calculation method makes. Another limitation is that, as with thermal transmittance, the simplified calculation method cannot be used to analyse condensation risk or surface temperatures at thermal bridges.

These limits on the method’s usefulness may not always be clear to the end user of a condensation risk analysis. It’s essential that insulation manufacturers are diligent in providing project-specific advice as to whether the Glaser method is right for a proposed construction.

Despite all of these seeming drawbacks, BS EN ISO 13788 remains a worthwhile tool.

“The method acts as a useful check that conventional wall and roof constructions have been specified appropriately, and that proposed vapour control measures should be capable of avoiding condensation issues occurring within the construction,” says David Milner.

He adds: “Moisture accumulation within a building element, especially at the insulation layer, can reduce thermal performance. That’s a health and comfort issue for building occupants. In the worst cases, condensation build-up over time could even be a structural issue. Getting design and specification right to avoid condensation risk is vital and must be backed up by a high standard of installation on site.”

Read our blog post looking at understanding and mitigating condensation risk in more detail.

What is BS 5250?

First published in 1989, BS 5250 was traditionally the code of practice for control of condensation in buildings. The standard was expanded in 2021 to address moisture in buildings more widely, leading to the new title of BS 5250:2021 Management of moisture in buildings. Code of practice.

Condensation risk is just one form of moisture risk in buildings, and the updated standard addresses a host of potential moisture issues in different types of construction. In particular, it focuses on the need for joined up thinking between design and construction phases.

“Most insulation-related standards focus on product performance rather than installation,” says David Milner. “While some documents, such as BS 5250 and BS 8212, provide guidance on insulation installation, there is still a gap in comprehensive, widely adopted standards specifically addressing insulation installation best practices. This is where third-party certifications like BBA and NHBC, together with government and industry association guidelines, play a crucial role. We use these relevant sources of knowledge to give our product advice.”

As such, BS 5250:2021 is arguably essential reading for all construction professionals. While its focus is on moisture management, following its principles and considering the link between design and specification can have knock-on benefits in terms of achieving the best possible performance from installed insulation.

BS 5250:2021 adopts a whole-building approach, considering a host of potential interactions between different areas of building design and construction. As part of those considerations, it offers guidance on appropriate forms of condensation risk analysis for different construction types – including when it is appropriate to use BS EN ISO 13788, and when it is not.

For the lowest-risk forms of construction, BS 5250 suggests that no condensation risk analysis is necessary. Where constructions face particular risks, or are subject to more complex moisture movements, a more thorough form of analysis to BS EN 15026:2023 is recommended (perhaps using simulation software called WUFI®, or similar). For other build-ups in between, the Glaser method is appropriate.

The Celotex U-value calculator and other support tools and services

The Celotex online U-value calculator has always been one of our most-valued tools. With no login required, you can obtain U-value calculations at your convenience. Technical specifications and installation resources for Celotex products are also available, allowing you to build complete project-specific specifications.

Find out more about the comprehensive tools we have available, including U-value calculations. Contact our technical support centre for further advice.