Polyfoam XPS has launched a new email newsletter to share information about construction products and standards, and to highlight useful resources for designers and specifiers.

‘The Build-Up’ arrives in email inboxes on the last Friday of every month, and is free to subscribe to. Each issue is also subsequently published in our News & Blog section of this site.

The short, easily digestible email highlights books, podcasts, magazines and other construction-related resources that can help designers and specifiers to achieve their project goals. It also includes a selection of inspiring news articles that readers may have missed elsewhere.

“We wanted to create something that aligned with our values of providing high quality insulation products and technical services,” explained Rob Firman, Technical and Specification Manager at Polyfoam XPS.

“As an insulation material, extruded polystyrene is robust and provides reliable long-term performance. Achieving quality in the design of construction projects, and ensuring that quality and performance translates to site, is essential for our industry to contribute to a sustainable future.”

Subscribe to ‘The Build-Up’ here and for a taste of the newsletter’s format and content, see this blog post version of the first issue, sent out in early 2021.

For any queries relating to Polyfoam XPS, our newsletter, or extruded polystyrene generally, contact us.


Polyfoam XPS - The Build-Up

This month’s edition of The Build Up focuses on product manufacturing. We’re nearing the halfway point of the year, which means we’re also nearing the halfway point of the transition period from CE marking to UKCA marking.

What does that mean for the products you specify? We’ll try to answer that question, as well as give our regular round-up of news stories and useful design resources.

If there are any topics you’d like to see us cover in the newsletter, or if you have any feedback on what we’re sending out each month, you can contact us us at any time, or reach us via LinkedIn.

Demystifying Standards

Architects and specifiers are often told that they need to know all about standards and codes of practice. But many standards are big documents with a hefty price tag, meaning they are not always accessible or digestible.

Our new blog post series is demystifying some of those standards. We’re explaining how we apply them as part of providing you with extruded polystyrene (XPS) insulation products, and technical services such as U-value calculations. This month, we’ve chosen to focus on BS EN 13164 – what it is, how it relates to CE marking, and the transition to the UKCA mark.


What do architects need to know about BS EN 13164?

BS EN 13164 is one of a number of harmonised European Standards relating to the manufacture of thermal insulation products for construction. It covers extruded polystyrene (XPS) specifically. Read More.

Design Resources

The Get It Right Initiative, known as GIRI, is working to promote a culture within UK construction of learning from mistakes and seeking to eliminate error. Making improvements in this area would reduce waste and potentially save billions of pounds.

One of their resources is the Guide to Improving Value by Reducing Design Error, produced by the GIRI design working group.

At the end of 2020, GIRI hosted a webinar featuring the co-founder and director of the Designing Buildings Wiki. The session focused on knowledge sharing, and how better knowledge sharing can help to reduce error.

Technical Support for BS6229

Getting More From Polyfoam XPS

As this month’s new blog post looks at manufacturing standards for thermal insulation products, it’s worth recapping what Polyfoam XPS produces at its Hartlepool plant.

We manufacture extruded polystyrene insulation, in accordance with BS EN 13164, for use in ground floor and inverted roof applications. You can view our complete range of Floorboard and Roofboard products, as well as accessories such as Slimline Zero WFRL for inverted roofs.

Product literature, declarations of performance and BBA certificates are all available online, or you can contact us to discuss which XPS product is best suited to your project.


What Caught Our Eye This Month ?


Thanks for reading this issue of The Build Up by Polyfoam XPS. To ensure you receive next months issue please subscribe.


Regulations and policies

BS EN 13164 is one of a number of harmonised European Standards relating to the manufacture of thermal insulation products for construction. It covers extruded polystyrene (XPS) specifically. The procedures outlined in the standard allow manufacturers to produce Declarations of Performance, conform to the Construction products Regulations, and affix the CE mark.

As a consequence of the UK leaving the European Union, the CE mark will no longer be recognised in the UK from the beginning of 2022. A new mark, the UK Conformity Assessed (UKCA) mark, will apply from that date.

What are harmonised standards for insulation products?

There is a sequence of harmonised European standards, each relating to a different thermal insulation type. For reference, the full list is as follows.

  • BS EN 13162 – mineral wool (MW) products.
  • BS EN 13163 – expanded polystyrene (EPS) products.
  • BS EN 13164 – extruded polystyrene foam (XPS) products.
  • BS EN 13165 – rigid polyurethane foam (PU) products.
  • BS EN 13166 – phenolic foam (PF) products.
  • BS EN 13167 – cellular glass (CG) products.
  • BS EN 13168 – wood wool (WW) products.
  • BS EN 13169 – expanded perlite board (EPB) products.
  • BS EN 13170 – products of expanded cork (ICB).
  • BS EN 13171 – wood fibre (WF) products.

All of these insulation standards follow a similar structure. They cover certain core product characteristics common to each material: thermal resistance and thermal conductivity; dimensional properties of length, width, squareness, flatness and thickness; the reaction to fire of the product as placed on the market; and durability characteristics.

As necessary for each product type, the standards also cover characteristics relating to specific applications.

Products are not expected to meet a particular level of performance for any characteristic, and the standards confer no judgement of fitness for purpose. Rather, the standards give the declarations that should be made when performance falls into certain brackets for each characteristic. It is these declarations that are published in the technical literature of manufacturers.

What do architects need to know about BS EN 13164?

Architects and design professionals do not need to be familiar with the contents of the insulation-related standards. It is enough to be aware that thermal insulation products are the subject of harmonised standards, and conformity assessed accordingly as an indication of quality and safety.

Harmonised standards put the onus on the product manufacturer by ensuring that similar types of products are manufactured, and their performance declared, in accordance with a common process and technical specification.

As part of that process, manufacturers have to demonstrate that they operate with a Factory Production Control (FPC) quality process in place. It is compulsory to declare certain performance characteristics of the product, while the declaration of others is at the manufacturer’s discretion depending on the product’s intended end use.

Declarations of Performance are another compulsory element of harmonised standards and CE marking, and are available on manufacturers’ websites. They indicate all of the characteristics covered by the particular standard and show the relevant declared results.

When is the CE mark changing to the UKCA mark?

As a result of leaving the European Union, the CE mark will no longer apply in the UK. Products intended to be sold in mainland Britain must instead bear the UKCA (UK Conformity Assessed). Different arrangements apply in Northern Ireland, featuring a combination of the UKNI mark and the CE mark.

UKCA marking started at the beginning of 2021. Where a standard still aligns with Europe, such as with BS EN 13164, an agreed transition period means that CE marking continues to be recognised in the UK until the end of 2021. At that point, only UKCA marked products will be recognised in mainland Britain. The UKCA mark, meanwhile, carries no weight in Europe.

In the short term, specifiers should see little change and XPS insulation will continue to be conformity assessed to BS EN 13164. As time goes on, however, and standards and legislative frameworks in the UK diverge from those of our European counterparts, more change might become evident.

As a manufacturer of extruded polystyrene, Polyfoam XPS manufactures and tests its products, and assesses them for conformity, against BS EN 13164. We manufacture at our Hartlepool plant and offer products for sale to the UK market.

As a result, we have already liaised with the relevant assessment bodies and begun to affix the UKCA mark to our XPS boards, instead of the CE mark.

We hope this answers any queries you may have had about CE marking, the UKCA mark, and the manufacture of thermal insulation products in the UK. For more information, you can view our product range, read more articles on our blog, or contact us with any further questions.



A new white paper from Polyfoam XPS is helping designers and specifiers of inverted roofs to understand how systems perform and are certified.

“Getting the right thickness of insulation in an inverted roof means taking account of several factors relating to moisture exposure and rainfall,” said Rob Firman, Technical and Specification Manager at Polyfoam XPS.

“We want to give readers of our white paper the confidence to understand how those insulation thicknesses are arrived at, so they know that their designs will perform as intended once installed on site.”

Third-party certification acts as reassurance for construction professionals that manufacturer’s claims are accurate. However, despite clearly defined standards and calculation procedures, an alternative interpretation of how inverted roofs perform is potentially risking specifiers including too little insulation.

“Our aim was not to say that one solution or certification body is right and another wrong,” continues Rob Firman. “What the white paper shows is that there’s actually little difference between the two interpretations.

“Unfortunately, the way in which the different interpretations are being communicated is not as clear as we believe it could or should be. Our aim is to give designers and specifiers the information they need to make sure they are considering comparable solutions and achieving the performance they intend.”

Download the Polyfoam XPS white paper about the performance and certification of inverted roof systems:

Polyfoam Inverted Roof White Paper

For any queries relating to inverted roofs and the topics discussed in the white paper, contact us.


Polyfoam XPS - The Build-Up
Welcome to The Build Up, the Polyfoam XPS email newsletter. This month we’re focusing on flat roof design and specification, including how to achieve inverted flat roofs that perform as intended. As well as the usual round-up of news stories that have caught our eye, this month’s resources include a new white paper we’ve put together.

Demystifying Standards

Architects and specifiers are often told that they need to know all about standards and codes of practice. But many standards are big documents with a hefty price tag, meaning they are not always accessible or digestible.

Our new blog post series is demystifying some of those standards. We’re explaining how we apply them as part of providing you with extruded polystyrene (XPS) insulation products, and technical services such as U-value calculations. This month it is the code of practice for flat roofs, BS 6229.

guidelines folders

What do architects need to know about BS 6229:2018?

Design Resources

    • Inspiration to achieve better buildings doesn’t come much better than Passive House + magazine. Every issue features multiple in-depth case studies telling the stories of low energy new-build and retrofit projects. Each is illustrated with site photos and supported by in-depth technical detail of how the end result was achieved. Comprehensive news articles, enlightening expert columnists, and technical examinations of current building performance issues complete each highly readable edition.


  • Although focused on helping to put London “on the path to a zero carbon future”, the London Energy Transformation Initiative (LETI) is creating resources that any construction professional can apply to their work, wherever they are based. Their Climate Emergency Design Guide is helping architects to approach a topic for which no formal standard currently exists, while documents like this Net Zero 1-Pager give a useful summary for anyone looking to engage with this complex topic.

Getting More From Polyfoam XPS

We’re excited to launch our new white paper, which is a detailed look at how the performance of inverted roofs is assessed and certified. If buildings are going to perform as they were designed to then it’s essential that designers and specifiers have confidence in the products and systems they select. This white paper explains everything you might look for in an inverted roof system.


What Caught Our Eye This Month ?


Thanks for reading this issue of The Build Up by Polyfoam XPS. To ensure you receive next months issue please subscribe.


Polyfoam XPS - The Build-Up
Welcome to the first issue of the Polyfoam XPS email newsletter The Build-Up. Every month we’re putting together a round-up of useful resources and interesting news, focusing on delivering quality across design, specification and construction.

About Us

Polyfoam XPS Ltd is a leading manufacturer of closed cell, extruded polystyrene insulation. Through our Floorboard and Roofboard ranges, Polyfoam XPS Ltd offers high quality, high performance, rigid, closed cell, extruded polystyrene (XPS) insulation for use in domestic, commercial and industrial buildings alike.

Demystifying Standards

Architects and specifiers are often told which standards or codes of practice they should be working to, and what they need to know about them. But many standards are big documents with a hefty price tag, meaning they are not always accessible or digestible.

In a new series of blog posts, we’ll demystify some of those standards. We’ll explain how we apply them as part of providing you with XPS insulation products, and technical services such as U-value calculations.

Technical Support for BS6229

What do architects and design professionals need to know about BR 443?

Any designers who perform their own U-value calculations should already be familiar with BR 443 and be applying its conventions. For designers who obtain calculations from elsewhere, however, do they need to know what is in the document? Read more

Design Resources

  • 99% Invisible is a long-running, design-focused, US-based podcast. Episodes cover building design, climate change and much more. We recommend browsing the archive and picking whatever sounds most interesting to you, but a good starting point is the episode about the invention of air conditioning and how it influenced the outcome of the 1980 US election.
  • In Designed to Perform, architect Tom Dollard offers practical advice on how to address the performance gap in buildings. Illustrated throughout with comprehensive thermally modelled details, the book identifies common building fabric issues and offers the solutions to create comfortable, low energy homes.
A construction office

Getting More From Polyfoam XPS

In need of more technical insight after reading this newsletter? The Polyfoam XPS blog is a hub for information about XPS insulation, ground floor and flat roof design and construction, relevant standards, and industry issues. Not sure where to start? Our most popular post is Bearing the Load: Floorboard Insulation, or you can browse the blog and pick out topics of interest.

What Caught Our Eye This Month ?


If you’re reading this it’s because you’ve contacted us for technical advice in the past, or you’re listed in an industry directory as willing to be contacted. We don’t want to be a nuisance or an unwanted presence in your inbox, so you’ll only receive future issues if you choose to subscribe. To subscribe please click here


Flat roof

BS 6229:2018 Flat roofs with continuously supported flexible waterproof coverings. Code of practice describes best practice for the design, construction and maintenance of flat roofs. A flat roof is defined as having a pitch of no greater than 10 degrees to the horizontal, but the recommendations in BS 6229 can be applied to roofs with a steeper pitch.

The standard is not an adopted European or international standard, and its contents are guidance and recommendations only. But as a code of practice developed by the UK flat roofing industry, BS 6229 carries weight.

What is in BS 6229?

The standard recognises four types of roof system: warm, inverted, cold and uninsulated flat roofs. It also emphasises the heightened risk of condensation caused by hybrid roof constructions.

The guidance applies to roofs with a timber, concrete or metal deck; the waterproofing types addressed by the standard are hot and cold liquid applied systems, reinforced bitumen membranes, plastic and rubber sheets, and mastic asphalt.

Two key areas of guidance are drainage and thermal performance.

Advice on minimum falls sets out how to ensure that a roof drains properly, including avoiding back falls in a zero falls flat roof. To aid detailing, BS 6229 includes typical level access arrangements for the different roof systems.

Thermal performance guidance includes the calculation of U-values (such as using the conventions of BR 443), how to treat point thermal bridges that prevent the installation of continuous insulation, and what correction factors to apply to inverted roofs. There are also short sections covering green and blue roofs.

There is limited guidance on condensation risk analysis, as the authors of BS 6229 agreed that the topic is better covered by BS 5250 Code of practice for control of condensation in buildings. There is some specific guidance relating to winter condensation risk in flat roofs, however.

The rest of BS 6229 lists commonly used flat roofing materials and relevant standards, highlights issues relating to workmanship, and describes how roof inspections and maintenance can ensure the system achieves its desired service life.

Should designers and specifiers be familiar with BS 6229?

Even if your workspace isn’t home to a copy of BS 6229:2018, there’s a reasonable chance you already apply a lot of its principles in your work. Many of the recommendations become widely disseminated through blog posts, articles, training presentations and manufacturer literature.

It’s possible, therefore, that you’re more familiar with the standard than you realise. But issues can arise if the recommendations are not taken into account at the right stage of the design process.

For example, it’s not uncommon to see detailed drawings where the correct minimum fall has not been allowed for. A project may be at detailed design stage or, even worse, already on site, and it comes to light that the falls need to be adjusted. If not, the insulation layer may run straight into a door threshold, or there may not be space to accommodate the necessary height of upstand above the roof finish.

The question is therefore asked: is there a thinner insulation product we can use? What is the minimum thickness of insulation we can get away with? We see a lot of flat roofs where a portion of the roof does not achieve the threshold U-value of 0.35 W/m²K (stated in BS 6229) to avoid surface condensation, because some compromise has had to be made in the design.

As an extruded polystyrene (XPS) insulation manufacturer supplying inverted roof systems, Polyfoam XPS strives to ensure that all technical support offered to designers and specifiers reflects the guidance of BS 6229:2018. We offer guidance on avoiding hybrid roof constructions, provide U-value calculations that accord with the recommendations, and apply the winter condensation risk adjustment as standard.

We can only do that, however, at the stage that we are involved in a project, which is sometimes too late to avoid compromises that affect the quality of projects. Design professionals should be familiar with BS 6229, and apply its principles from the outset.

About Polyfoam XPS

You can contact us at any stage of a construction project to discuss questions relating to inverted roofs and applying the principles of BS 6229:2018. Alternatively, download our inverted roof BBA certificate to gain an understanding of which of our products can be used in inverted roofs, and how.

We have also published an in-depth white paper looking at the assessment and certification of inverted flat roofs. It details aspects of BS 6229 that address how inverted roofs perform thermally, and discusses issues relating to different methods of assessing that performance.

For more on XPS insulation, browse our blog posts or find out more about us as a company.


BRE Report (BR) 443 Conventions for U-value Calculations is a document produced by the Building Research Establishment in the UK. As its title suggests, the report details best practice that should be followed by anybody carrying out U-value calculations for building elements.

Although it is not a European Standard (like others that detail actual calculation methods for thermal transmittance), or even a British Standard, BR 443 carries weight in UK construction. It is a widely used and referenced document, recognised as essential to providing accurate U-value calculations.

What is in BR 443?

One thing that BR 443 is not is an explanation of calculation procedures. The document does not describe how to perform a U-value calculation.

What it does give is dimensional and performance data about common UK construction materials and methods. Using BR 443, people who carry out U-value calculations can represent those materials and construction methods consistently, ensuring the industry generally benefits from accurate calculations.

BR 443 contains a wealth of supporting guidance about applying the data, meaning users of calculation software can make informed decisions about inputs into calculation software. There are also checklists for common building elements covering different factors that need to be taken into account when calculating a U-value for that element.

At the time of writing, BR 443:2019 is the current edition, having replaced the one published in 2006. The 2019 document is approximately double in length compared to its predecessor, providing more useful information for readers and significantly expanding some sections (such as section 11 about windows and glazed elements).

A small amount of previous guidance has been removed but, for the most part, the data provided for use in calculations have remained the same. The biggest difference is in the quantity of supporting information.

Traditionally, BR 443 was free to download, but the 2019 edition has to be paid for. As the 2006 edition is still available online, anyone searching for the document should satisfy themselves as to which version they have accessed.

What do architects and design professionals need to know about BR 443?

Any designers who perform their own U-value calculations should already be familiar with BR 443 and be applying its conventions. For designers who obtain calculations from elsewhere, however, do they need to know what is in the document?

Technically, no. The main thing is to be satisfied that whoever is providing calculations for your projects knows BR 443 and is working to its conventions. There are some reasons why having an understanding of its contents could be beneficial, however.

Awareness of common material data, or factors that impact on the thermal performance of building elements, could help to inform design decisions or material specification choices. By factoring that awareness into projects at an earlier stage, it could make it more likely that design intent is realised later on. By contrast, late design and specification changes to compensate for different thermal properties can lead to compromises being made.

Another reason is that when receiving calculations from a third party, such as a consultant or product manufacturer, it’s possible to read those calculations, understand the data that has been used, and ask any questions about the correct representation of your design. Trust that the third party is working to current conventions is important, but being satisfied that you have communicated your design correctly and that it will help to achieve the goals of the project is equally important.

About Polyfoam XPS

As part of the technical support we offer to the construction industry, Polyfoam XPS provides U-value calculations that follow the conventions of BR 443 as standard.

If you have any questions about this blog post, or require advice about U-value calculations for your project, contact us.

Alternatively, to find extruded polystyrene (XPS) insulation products for your ground floor or inverted roof designs, view our complete range of products.


What is the difference between declared and design thermal conductivity (or lambda)?

‘Declared thermal conductivity’ is the lambda value of an insulation product as it leaves the factory. In the context of inverted roofing, ‘design thermal conductivity’ is the lambda value of the insulation once it has been adjusted for potential moisture absorption.

The difference between the two values depends on the insulation material. For a material that has very low water absorption, its thermal conductivity will be affected less because the material in situ is closer to the factory production specification. Where a material is capable of absorbing a relatively greater volume of moisture, its design lambda will be correspondingly worse.

How are declared and design lambda values established?

For an insulation product manufactured under a harmonised European standard, the thermal conductivity declared must be a ‘lambda 90/90’ value. That is, there is a 90% statistical certainty that 90% of tested samples have a thermal conductivity equal to or lower than the declared value.

The design lambda value used for the insulation product in U-value calculations for inverted roofs is the declared value with a moisture correction factor applied to it. The moisture correction factor varies depending on the material type, as described above.

Extruded polystyrene insulation, such as Polyfoam XPS Roofboard products inverted roofs, has a moisture absorption of just 0.7%. For a board greater than 100mm in thickness, that means the declared lambda is only adjusted from 0.033 W/mK to a design lambda of 0.034 W/mK. For further advice on the correct application of design thermal conductivity in U-value calculations, contact our technical team.


Can declared thermal conductivity be used in inverted roof U-value calculations?

When calculating the U-value of an inverted flat roof, the thermal conductivity of the insulation layer should be the product’s design lambda value and not its declared value. Because of the insulation’s position above the roof waterproofing layer, it is expected to be exposed to some rainfall and therefore a moisture correction factor should be applied accordingly.

Testing of inverted roof systems carried out in accordance with the technical guidance document ETAG 031 often generates a result that suggests water does not penetrate the system. In accordance with BS 6229:2018 and, by extension, BBA Bulletin No. 4, the inverted roof installation above the waterproofing should not be assumed as waterproof – meaning only design values are appropriate.

What happens if the declared lambda is used for inverted roof U-value calculations?

Using declared thermal conductivity in an inverted roof U-value calculation gives an unrealistic impression of the performance of the roof. If the chosen insulation product has a relatively high water absorption value then when it is exposed to moisture the rate of heat loss will be much higher than allowed for in compliance calculations.

Find out more about the low water absorption of Polyfoam XPS’s extruded polystyrene (XPS) insulation boards, and the different methods by which it is tested. Contact us for reliable and accurate inverted roof U-value calculations featuring the design lambda values of our Polyfoam Roofboard Extra and Roofboard Super products.