Questionmark in window mist

BS 5250 has always been an important standard for architects and design professionals to be familiar with. Until 2021 it was titled Control of condensation in buildings, but the publication of an updated and heavily revised version has widened its scope and it is now the code of practice for Management of moisture in buildings.

This wider-ranging approach emphasises a whole-building approach to moisture management. It seeks to identify possible risks, and presents guidance as it relates to both ‘as designed in theory’ and ‘as built/in service’ conditions. It therefore represents an even more comprehensive source of advice for designers and contractors than before.

Why does BS 5250:2021 deal with moisture management more generally?

It’s a commonly acknowledged issue that, as buildings get more airtight and more energy efficient, changes to ventilation provision have not kept pace to ensure the controlled replacement of stale air. Moisture vapour is a significant component of indoor air, exacerbated by social trends such as drying clothes indoors more often, all of which adds to the moisture content.

Warm, moist air combined with poor ventilation provision and thermal bridges in building fabric, all add to the risk of condensation occurring in buildings.

The retrofit of existing buildings is a significant issue in terms of whether the country can meet its net zero targets. Simply insulating existing buildings to reduce their energy consumption is not enough, as any retrofit design must take into account the need for ventilation and the moisture balance of the existing structure.

Applying energy efficiency solutions to existing building fabric must be done while taking into account factors like driving rain, and whether moisture might be pushed to other parts of the structure that are not currently affected by it.

Moisture risks in buildings therefore go well beyond ‘just’ condensation risk. And that’s without us taking into account climate change, the severity of extreme weather, risks of flooding, and potential changes to other moisture sources like the ground.

Does BS 5250:2021 still deal with condensation risk?

Large portions of the updated standard consist of comprehensive design guidance for floors, walls and roofs. The array of construction types covered under each element has been expanded, dealing with a much wider variety of materials and build-ups, and providing specific advice for each.

The altered scope of the standard means all of these constructions are assessed in terms of a variety of potential moisture sources. The text is careful to distinguish between design intent (‘as designed in theory’) and potential real-world issues that could be encountered (‘as built/in service’), giving designers useful context to consider when producing details and specifications.

Nevertheless, condensation risk is still a part of BS 5250:2021. As before, the standard distinguishes between the Glaser method detailed in BS EN ISO 13788, and more detailed assessment carried out in accordance with BS EN 15026.

Guidance is given as to when the simplified modelling provided by the Glaser method is appropriate (and, indeed, occasions when it is not). The standard also makes clear about occasions when calculations are not required at all because there is clear prescriptive guidance on how to avoid risks.

Because ISO 13788, the standard underpinning the Glaser method, has not changed, designers should not expect to see substantial changes to condensation risk analyses produced by construction product manufacturers using common industry software.

Where can I get a summary of the guidance in BS 5250:2021?

Our philosophy behind this series of blog posts looking at standards, and what we think designers and specifiers really need to know about those standards, has been to make them more accessible. By highlighting the key points, we’ve tried to make you more aware of the useful elements of standards without necessarily having to purchase them.

BS 5250:2021 is different to all of the other standards we’ve looked at so far. All of its contents are useful, and are written in accessible way that will help you apply the principles and recommendations to your projects.

As we saw above, elements of moisture risk are so different but also closely interlinked, making it impossible to pick out a series of key points that are universal to every project. The key with BS 5250:2021 is that every building project is unique, and therefore the way in which you will apply the standard could be different every single time you reference it.

We always say that standards are big documents that come with a hefty price tag, and it’s often not clear what you get for that price. In the case of BS 5250:2021, the value is there on every page, and it should be a document that every designer and contractor refers to regularly. Our view is not so much can you afford the standard, but rather can you afford NOT to buy a copy?

About Polyfoam XPS

Polyfoam XPS will continue to digest the comprehensive guidance of BS 5250:2021. We manufacture extruded polystyrene (XPS) insulation for ground floors and flat roofs, so over the first part of 2022 we’ll look in more detail at some of the guidance relating to those applications specifically.

As we have highlighted in this post, however, no amount of summarising can hope to provide the same level of comprehensive advice contained within the standard.

Find out more about Polyfoam XPS and our complete range of products, or learn more about current industry issues and product performance in our blog. Alternatively, to find out how we can help with flooring or roofing solutions for your project, contact us.


Man typing

Product data and product information supplied by manufacturers in the construction industry is currently the subject of much debate and discussion.

For architects and specifiers to make informed decisions about which construction products will help them to deliver safe, healthy and comfortable buildings, product data must be relevant, accurate and up to date.

Underpinning all of this is the goal of achieving a ‘golden thread’ of information on construction projects. The golden thread is a concept that was endorsed by Dame Judith Hackitt as a way of improving safety in buildings and delivering design intent. Terms like ‘golden thread’ can mean different things to different parties, having slightly different definitions depending on the way that different parties use information and data.

What is the difference between construction product information and product data?

Much like the concept of the golden thread, the ways in which people and organisations define information and data relating to construction products can vary.

Speaking as a construction product manufacturer, Polyfoam XPS generally views its data as being ‘raw’ information related to the product itself. Product data describes the performance of our products as determined by testing, whether carried out by ourselves or an independent third party.

Product information, meanwhile, can feature product data, but puts it in a wider context – for example by explaining how the product was tested, or explaining the meaning of a test result so that a specifier knows how to interpret the result.

The Code for Construction Product Information (CCPI) has been developed during the course of 2021, and defines product information as: “Any information about a construction product made available to internal and/or external stakeholders. This includes but is not limited to, product information given in writing, in print, online, electronically or in an advertisement.”

Why is digital product data important?

However you define product data and product information, making information available and accessible is essential for specifiers to be able to use it with confidence. Digitised product data is a key aspect of the golden thread, as The Institution of Engineering and Technology (IET) has explored thoroughly in their plain language guide, Digitisation for construction product manufacturers.

While the guide has very much been written with product manufacturers as the target audience, the topics explored by the guide are important to specifiers as well. There are clearly written sections looking at the role of product data post-Grenfell, and the place that 3D BIM objects have in the digital landscape.

Developing an understanding of these topics can help specifiers to have more informed conversations with product manufacturers. Through this kind of dialogue, both parties can develop ways of working that will help make the golden thread a reality.

How is Polyfoam XPS managing its product data and product information?

One of the most significant impacts of both the CCPI and the IET’s report is the impetus they have generated within manufacturers’ organisations to assess existing processes and look for areas of improvement. That is something we have done, and continue to do, at Polyfoam XPS.

While we continue to evaluate our internal data management and examine what the concept of ‘structured data’ would mean for us, Polyfoam XPS remains a partner with NBS. That means you can find our products on NBS Source, a free-to-use construction product platform that allows you to quickly and easily find, select and specify our products.

Product data is available in NBS standardised specification format, and our profile includes our third-party certification, giving the detailed information needed to make informed product decisions.

Our NBS Source links are also available in the technical support area of our website, where you can contact us about your project, read more posts from our blog, view our online CPD session, or subscribe to receive our monthly newsletter.



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.



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.


Coronavirus Update

After careful consideration, and in light of the rapidly changing market conditions, we at Polyfoam XPS have taken the decision to temporarily reduce the level of our operations.  

From Friday 3rd April we will be reducing our operation and staff levels within our warehouse, offices and sales team. We endeavour to continue to do our best to support customers working on key projects that meet the increased needs of the national healthcare efforts, whilst following Government guidelines. 

Please consider that we are operating with a skeleton staff and will not be working to the normal levels of service. We appreciate your understanding during this difficult time.

For urgent sales or technical enquiries please contact:

Customer Services      sales@polyfoamxps.co.uk       01429 855100    Sales enquiries            ian.exall@polyfoamxps.co.uk  07500  975534 Technical enquiries     technical@polyfoamxps.co.uk  01429 855120

This decision has not been taken lightly but our priority is to ensure the health and wellbeing of our colleagues, customers and suppliers. We will continue to monitor the situation carefully and will keep you updated with any further changes.

Thank you for your ongoing support and we wish you, your families and colleagues the very best.

Stuart Bell
Managing Director
1st April 2020


CPD Member Logo

Polyfoam XPS, a leading manufacturer of extruded polystyrene (XPS), has launched its first Continuing Professional Development (CPD) module on flooring.

Aimed at architects and specifiers, the CPD seminars will provide expert advice on the key differences between rigid insulation types for flooring and the impact these can have on a building’s thermal and load bearing performance.

The training includes guidance on which insulation should be specified for different ground floor constructions, including those required for refurbishment projects and involving vehicular traffic.

Rob Firman, Technical and Specification Manager of Polyfoam XPS said: “The launch of our CPD programme follows our own research, which revealed a number of misconceptions about flooring insulation. The performance characteristics of insulation products vary considerably, so it is important to make the right choice.

Having a greater understanding and knowledge of these characteristics, can help reduce risks on site and ensure ground floor constructions perform as expected.

Led by Rob Firman, the Polyfoam XPS CPD is accredited by the CPD Certification Service. Seminars are free of charge and will last for one hour at locations to suit.

To enquire about the CPD or book a seminar, call 01429 855120 or complete the CPD enquiry form.


ISO 45001 stamp

Polyfoam XPS has achieved the newly launched ISO 45001 international standards for Occupational Health and Safety Management Systems.

The manufacturer of extruded polystyrene has been approved and certified to the standard following an external audit from Bureau Veritas Certification.

The achievement reflects the robust systems that are in place at the Polyfoam XPS headquarters in Hartlepool, that prevent work-related injury and ill health, and proactively improve its occupational health and safety performance.

Stuart Bell, managing director of Polyfoam XPS, said: “The continuous development of our management systems underpins this achievement and demonstrates our ongoing commitment to improve all aspects of our business.

We are rigorously audited to maintain accreditation to all our certified standards. This ensures we can continue to provide a professional service that meets our customers’ requirements, and that we can identify and reduce operational risks within our business.”

ISO 45001 replaces OHSAS 18001 in March 2021.


NBS National BIM Library Endorsement Stamp

Polyfoam XPS, a leading manufacturer of extruded polystyrene (XPS), has renewed its partnership with NBS to host its growing range of insulation products in the NBS National BIM Library.

A total of seven Polyfoam XPS products can be found on the site, including three grades of Polyfoam Floorboard, providing thermal insulation for loadbearing floors, two grades of Polyfoam Roofboard providing thermally-efficient insulation for flat roofs, the Polyfoam Slimline Zero Membrane, and the Polyfoam Upstand Board for the thermal insulation and protection of upstand and parapet walls.

Free to use, the NBS National BIM Library is the only one of its kind to link directly to market-leading specification software allowing designers to drag and drop objects into a model.

RIBA Product Selector Endorsement Stamp

The partnership also means that information about Polyfoam XPS products, including technical downloads and independent accreditations, are featured on ribaproductselector.com.

Rob Firman, Technical and Specification Manager of Polyfoam XPS said: “The NBS offers trusted specification platforms, which are used across the whole construction sector. Partnering with the company ensures our products are available to designers as high-quality BIM objects and that they are armed with all the technical information they need to make informed decisions.”

All Polyfoam XPS products are available in the BIM Library in IFC format as well as 3D CAD Autodesk Revit.


Hartlepool Plant

Ravatherm UK, the Polyfoam XPS insulation manufacturer, has been acquired by a private investor.

The deal means that from 1st October 2018, the Hartlepool-based business will operate under a new name – Polyfoam XPS. The company’s manufacturing plant will continue to run as normal with no employees affected by the change. All products will also remain the same, including their certifications.

Stuart Bell, managing director of Polyfoam XPS said: “The Polyfoam brand was established more than 30 years ago, so is already well known and respected in the building industry. This made it the natural choice for the new company name.

“With the new name, comes a new look which will be reflected on our website and other marketing materials, but aside from that, it’s very much business as usual. We will continue to operate in exactly the same way as before, so there will be no disruption for our customers.

“Our focus will continue to be on providing high-performance extruded polystyrene products with unrivalled green credentials and backed by leading levels of customer service.”


In response to customer demand Polyfoam™ XPS, extruded insulation manufacturer, has launched three new floorboard products offering specifiers and contractors a greater choice of thicknesses.

Adding to the company’s Floorboard Extra range, the new XPS insulation products are available in a thickness of 60, 125 and 150mm.

Speaking about the launch, Stuart Bell, managing director at Polyfoam XPS said: “We work closely with our customers to understand their needs to ensure we can continue to offer the right product mix.

“We recognised that there was a growing demand for different insulation thicknesses for new floor construction, so have responded by developing three new products aligned to specific customer requests.

“Polyfoam Floorboard Extra in 125mm and 150mm are now the thickest products in the range and will prevent installers from having to double layer the insulation boards to achieve certain U-values. This will help to reduce costs and labour time.”

The new products mean that Polyfoam Floorboard Extra is available in nine different thicknesses ranging from 25 – 150mm.

Suitable for almost any floor construction in domestic or industrial properties, Polyfoam Floorboard Extra is highly resistant to compression and water absorption and offers thermal conductivity of 0.033 W/mK.

All products in the range achieve a BRE Certified Green Guide rating of A+, have product-specific Type III Environmental Product Declarations and are 100% recyclable.

Polyfoam XPS carries out U-value calculations free of charge for building designers involved in the construction of ground floors.