Ian Exall

Ian Exall, National Sales Manager of Polyfoam XPS gives his view.

Fundamentally, price remains the driving factor on construction projects, but priorities have shifted. The focus is no longer on specifying or purchasing the cheapest products. The priority for most of our customers is value for money. They want affordable products, but which can still perform to high standards and are seeking assurances through third party guarantees and certifications such as BBA before purchasing. Cost certainty is another key consideration, which is being fuelled by Brexit and fears of the unknown. We are getting lots of requests for long-term pricing for projects, especially for larger schemes which could take two years or more to complete. Many contractors are worried about the risk of product and labour inflation, so want the assurance that prices will remain stable despite potential changes to market and/or economic conditions. Whilst this is understandable, it simply moves the risk along the supply chain where margins may be insufficient to withstand potential inflationary pressures. At the same time, we have noticed a big crackdown on specification switching and so has our distribution network. This is a trend which follows the recommendations in the Hackitt Review and the push for more competency across the construction industry. Long-term, this will have a positive impact on our sector as switching specified insulation during construction can lead to inaccurate U-values and potential non-compliance with Building Regulations. However, following the Grenfell tragedy, minimising risk is another priority for construction professionals and this is affecting all aspects of the industry, including specification. As a result, we are seeing some insulation specifications being held even if there is a better product available both in terms of cost and performance. This suggests that roofing contractors, main contractors and other specifiers are reluctant to take on the responsibility of any liability that may come with such a change. Uncertainty won’t go away in 2019 and inevitably, that means our customers will continue to put price in the priority list but it’s no longer just a numbers game. The whole industry is moving towards a more forensic approach that shines the spotlight on quality, performance and risk, and this will continue to affect purchasing decisions. For manufacturers of construction products, this underlines the ever growing need to provide assurances, advice and support which help contractors and specifiers make more informed decisions. This commentary appeared in the January 2019 edition of Total Contractor


Amendments to Building Regulations for fire safety

December 2018 saw the publication of amendments to the Building Regulations in England, as part of the response to the Grenfell Tower disaster. The amendments came into effect in January 2019.

Which areas of the Building Regulations have been changed?

Part B of the Building Regulations, supported by the guidance published in the two volumes of Approved Document B, is the natural starting point for looking at what has been altered.

Two amendment documents have been published and are available via the government website. The first covers both volumes of Approved Document B and consists largely of some new introductory text for the two volumes, re-numbering of paragraphs affected by the amendments, and some changes to the appendices.

The second document covers volume 2 of Approved Document B only (buildings other than dwellinghouses), and comprises a revised wording of requirement B4 (external fire spread), together with replacement text for the whole of section 12 (construction of external walls). There are also some changes to other appendices. The revision to requirement B4 and section 12 of volume 2 goes so far as to also include the text of the amended regulation 7 of the Building Regulations.

Regulation 7 deals with materials and workmanship, previously consisted of one paragraph only, and is supported by its own Approved Document. The decision to reproduce the text in the amendment to Approved Document B volume 2 arguably reflects the extent to which many construction professionals are unaware of the full extent of the Building Regulations and how they should be approached holistically.

Further paragraphs have been added to regulation 7 to make law the requirement to use materials of limited combustibility for the “external wall, or specified attachment, of a relevant building”. Paragraph 4 of regulation defines a ‘relevant building’.

As a manufacturer of extruded polystyrene insulation, Polyfoam XPS has received enquiries relating to the Building Regulations amendments, and the rest of this post explains our understanding of how the use of Polyfoam XPS products should not be affected by the published amendments.

The effect on XPS insulation – roof upstands

Where a flat roof meets an external wall, an upstand is required to help prevent the ingress of water to the building. To limit the cold bridging effect of the junction, the upstand should also be insulated, and Polyfoam XPS offers Upstand Board specifically for this application.

Some people have interpreted the upstand as forming part of the external wall. Where an upstand is on a ‘relevant building’ as defined by the revised regulation 7, their concern is that XPS insulation – which does not achieve a Euroclass A1 or A2 fire rating – is no longer appropriate.

However, paragraph 3 of the revised regulation 7 lists exceptions where the new requirement for materials of limited combustibility does not apply, including “any part of a roof if that part is connected to an external wall”.

The roof upstand constitutes part of the flat roof and it is therefore our view that a Building Control Body should continue to accept the use of a product like Polyfoam Upstand Board on projects that fall under the description of a ‘relevant building’ in paragraph 2 of regulation 7.

The effect on XPS insulation – balconies

The revised regulation includes not only external walls, but also ‘specified attachments’. A number of items are considered to be ‘specified attachments’, including “a balcony attached to an external wall”. This has led to concerns that where a flat roof designed as a balcony abuts an external wall, the materials in the flat roof should meet the requirement for limited combustibility.

Inverted warm roof constructions featuring Polyfoam XPS products are frequently designed as balconies. However, in these situations, if the balcony is insulated then that means it is over a heated space. It therefore becomes a thermal element in its own right – i.e. a flat roof – and is subject to all other necessary Building Regulations requirements – including fire safety.

Our view is that a balcony considered to be a ‘specified attachment’ is something essentially bolted on to the external wall, outside of the thermal envelope and considered on its own merit in terms of fire performance.

Should you or your Building Control Body have any questions or concerns about the use of Polyfoam XPS products on projects where this sensitive area of regulation applies, contact our technical helpline on 01429 855120, or email

Published February 2019.


Technical Support for BS6229

A revised version of BS 6229, the code of practice for ‘flat roofs with continuously supported flexible waterproofing coverings’, came into effect on 30th November 2018. As part of the wide-ranging update, the standard’s guidance about inverted roof construction was amended.

For more information about what BS 6229 covers generally, we have written a separate blog post.

BS 6229 guidance about the thermal performance of inverted flat roofs

In addition to a general description of inverted roof construction, paragraph is the section of most interest in terms of inverted roof construction. It describes how the thermal performance of an inverted roof should be established to include for the cooling effect of rainwater that penetrates the insulation layer and reaches the waterproofing.

This procedure should be familiar to anybody who regularly works with inverted roof insulation manufacturers or system suppliers. Thermal transmittance (U-value) is calculated following the method in BS EN ISO 6946, using the design thermal conductivity of the insulation and rainwater cooling correction, as specified in the accompanying guidance of ETAG 031-1, BRE Report BR 443, and BBA Information Bulletin No. 4.

Furthermore, the drainage factor, f, can be obtained from third-party testing and certification if available – such as Polyfoam XPS’s BBA certificate for flat roofing.

What has changed in BS 6229’s guidance on inverted roofs?

The 2018 revision features a supplementary note to paragraph It says that imperfections occur in the water flow reducing layer installed over the inverted roof insulation, due to poor workmanship, poor detailing, or post-construction damage, increasing the volume of water likely to reach the waterproofing layer.

In turn, that increases the water cooling effect on the insulation and worsens the in-service thermal performance of the roof, beyond what was anticipated at design stage. To compensate, the supplementary note suggests increasing the thickness of the insulation layer by 10% until such a time as further evidence and performance testing is available.

What are the issues with this revised inverted roof guidance?

Polyfoam XPS has a number of issues with this supplementary note in BS 6229: 2018.

The Standard’s foreword is clear that “notes give references and additional information that are important but do not form part of the recommendations”, but readers may not be aware of that. The inclusion of this note could lead people to wrongly assume their designs and installations do not accord with current best practice, even though the correct calculation procedures have been followed.

Standards are typically written assuming a good level of workmanship. Workmanship is a requirement of national building regulations, and it is impossible to make provisions for every scenario of something being installed poorly. It is unusual to see a comment included in a standard which assumes poor workmanship, for which evidence has not been gathered.

As a manufacturer supplying inverted roof insulation and water control layers, Polyfoam XPS is not aware of widespread workmanship issues. If the committee responsible for BS 6229 has evidence to the contrary then industry – including manufacturers like Polyfoam XPS – should be given the opportunity to respond and address those issues.

Instead, the suggestion of a 10% increase in insulation thickness feels arbitrary. If changes to insulation thicknesses are necessary then they should have been included in the recommendations upon the completion of evidence gathering and further testing – not as a potentially scare-mongering supplementary note in advance of any such exercise.

Mechanisms exist within the calculation method to achieve a similar level of caution, such as using an increased value for the drainage factor, f. It is not clear why the supplementary note, if it had to be written at all, did not suggest this, rather than an arbitrary percentage increase in insulation thickness.


If clients and customers are concerned about the quality of workmanship then we advise them to speak to their contractor. However, if they wish to explore a compensatory factor in their U-value calculations then we are happy to work with them to discuss a measurable level of caution.

Otherwise, the recommendations of BS 6229: 2018 are clear. The current method for calculating the thermal performance of inverted roofs is valid and does not require any change in current practice. Polyfoam XPS will therefore continue to abide by all existing calculation standards and guidance.

The LRWA have published further guidance on the topic and it can be found on the LRWA website. To discuss inverted roof U-value calculations in more detail, contact our technical helpline on 01429 855120, or email

Published February 2019 / Updated March 2020

WHAT IS BS 6229:2018?

What is BS 6229:2018

As a British Standard only (rather than an adopted European or International standard), BS 6229 concentrates on flat roof construction in the UK. It describes best practice in the design, construction and maintenance of cold, warm and inverted flat roofs with a fully supported, flexible waterproofing layer.

Like any British Standard code of practice, the contents of BS 6229 are guidance and recommendations only. The flat roofing industry collaborates to produce this standard, and the guidance therefore carries weight. Any claim of compliance, however, should be made with care – and any deviation from the recommendations should be justified if design and construction work is suggested to be compliant.

What is the current version of BS 6229?

The previous version of BS 6229 was published in 2003. The 2018 version acknowledges that many changes have since occurred in how buildings are constructed, and how waterproofing materials perform. BS 6229:2018 therefore represents a comprehensive and wholesale review of the guidance.

To avoid the duplication of information, BS 6229 no longer gives detailed information on condensation risk, workmanship or acoustics. Instead, it points readers in the direction of other standards specifically addressing those topics: BS 5250, BS 8000-4, and BS 8233 respectively.

What roof constructions does BS 6229 cover?

The standard gives advice and recommendations for flat roofs, which it defines as having a pitch of up to 10 degrees and a deck constructed from timber, metal or concrete. The “fully supported, flexible” waterproofing types referred to by section 5.4 of the standard are:

  • Reinforced bitumen membranes.
  • Mastic asphalt.
  • Plastic and rubber sheets.
  • Hot and cold liquid applied roofing.

Four types of roof system are recognised: warm flat roofs, inverted warm flat roofs, cold flat roofs, and uninsulated flat roofs. Reference is also made to hybrid flat roof constructions and the heightened risk of condensation for which they can be responsible. While BS 6229 does not say outright that hybrid roofs are not recommended, it does make clear that designers “should select the type of flat roof most suitable for the intended building”.

What other areas of roof design feature in BS 6229?

Drainage and minimum falls is a critical aspect of flat roof design. To aid good detailing, not only does BS 6229 state the falls that should be achieved, it also includes typical level access designs for the different roof systems.

Comprehensive guidance on flat roof thermal performance is offered, including how point thermal bridges should be treated when they prevent a continuous insulation layer being installed. A separate section is given over to the correction factors applied to inverted roofing (which we discuss in more detail in this blog post). Green and blue inverted roofs feature in their own short sections, including advice not to take into account any thermal performance of growing mediums for green roofs.

A short section introducing the topic of condensation risk analysis includes a recommendation to use an external temperature of -5 deg.C for 60 days during the heating season to allow for the cooling effect of clear sky radiation. While this has been a feature of the standard since the 1980s, awareness of it appears to be limited and is arguably not common practice in the industry.

Guidance on design issues concludes with sections on surface protection – which also addresses ballast for inverted roofs – and rooftop installations such as plant.

Roofing materials, workmanship and inspection

The remainder of BS 6229 lists commonly used materials for the roof structure, waterproofing, thermal insulation and vapour control layers, and gives standards and other applicable guidance to which they should be manufactured or prepared.

A short section about workmanship highlights some of the ways in which roof coverings can fail, and briefly describes how roofing materials should be cared for on site. Finally, a section on roof inspections and maintenance describes how best to ensure the roof system achieves its service life, and the role that a building information manual can play.

To discuss BS 6229 and roof system design in more detail, and how Polyfoam XPS insulation can be part of the roof system for your project, contact our technical helpline on 01429 855120, or email

Published February 2019.


Insulation matters: the importance of correct specification and installation

Poorly specified and/or installed insulation can have a detrimental impact on ground floors. Rob Firman, Technical and Specification Manager at Polyfoam XPS explains the risks and offers advice on what products to choose.

If you’re a flooring contractor, how far would you go to demonstrate that you have correctly constructed a floor?

Would you open it up to allow further inspection, knowing it would have to be made good again? What about opening up the floor, removing a sample of insulation, and trying to arrange with the manufacturer to have it tested to show the method of installation was not detrimental to its thermal performance?

At this point, you may be wondering why you would need to go to these lengths if the floor had been installed correctly – and the answer is that you wouldn’t.

However, these are the steps one contractor tried to take after they had constructed ground floors in a multi-unit residential development and omitted a crucial membrane layer below the rigid insulation boards.

A concern was raised that the floors did not match the specification, and that the insulation layer could be adversely affected by moisture.

Desperate to avoid redoing so much flooring work at their own expense, the contractor was willing to go to significant lengths to prove the performance of the insulation as installed. Unfortunately, with no standard method to check any measurement of thermal performance against, it would have been impossible for any test results to be recognised or accepted as accurate.

The risks of incorrect floors 

This is just one example of the many errors that can occur in the construction of ground floors. Genuine mistakes can, and do, happen, but there can be other reasons behind an incorrect floor which can be difficult to pinpoint. 

It could be the result of poor specification in the first instance. It could be due to misreading the specification, or not reading it at all and ‘doing things the way we’ve always done them’. In some cases, the specification may have been read correctly but an unsuitable product substitution offered or made for one of the floor’s layers. Or the errors could simply stem from the contractor not being up to speed with current floor construction practices.

But whatever causes an error in a floor construction, poorly specified and/or installed insulation is a significant concern, and should not be allowed to remain just because taking up the floor is considered inconvenient.

At worst, this could result in a failure of the floor. At best, it could mean the floor is sound but its intended U-value is not met – a risk that some in the industry seem willing to accept, even though it could rightfully be deemed not to comply with building regulations.

Choosing the right insulation 

For a flooring contractor, distinguishing clearly between different types of rigid insulation for ground floors may seem unnecessary. Some may assume the difference is minimal, but in fact, these products can be very different.

There is also a misconception that a more thermally-efficient insulation offers better performance in other respects. It is assumed that the product with the best thermal performance is typically the most expensive, so must also be the strongest. But that is not the case.

Different rigid insulation boards offer different combinations of characteristics. Some are more thermally efficient but unsuitable for bearing high structural loadings. Insulation materials with a higher compressive strength may need to be slightly thicker to achieve the required U-value but are more robust and tolerant of harsher environments.

The benefits of extruded polystyrene (XPS) insulation

Extruded polystyrene (XPS) insulation is one of the most common types of rigid board, but uniquely, it can be used in damp or wet environments without affecting its thermal performance. It can be laid directly on prepared ground, with the damp proof membrane laid over it also acting as the separating layer between insulation and concrete – a saving of both time and membrane material.

In addition, its high compressive strength makes it ideal for installing below concrete floor slabs, to the outside of basement structures and – where required by national building regulations – surrounding swimming pool basins.

As a flat, strong and dimensionally stable insulation layer, it can also be used under floating floor coverings like screed or chipboard, above the ground floor slab.

Alternatively, when used below raft slabs in residential and other low-rise buildings, XPS helps to enclose the building structure within the thermal envelope, reducing linear thermal bridging at junctions between construction elements, and achieving a greater level of building performance, comfort and energy efficiency.

Raising standards

Project quality and building regulation compliance depend on using the right material in the right situation. That’s why dispelling misconceptions about floor insulation is so important and why contractors must understand the qualities of the various types.
Installing the ‘wrong’ insulation board may seem like a small risk, but the impact could be bigger than you think. At a time when the construction industry is being scrutinised on how it delivers projects, such a risk should not be an option.

It is vital that contractors understand the floor insulation they’re purchasing and install it correctly. Not only will this prevent the need to open up completed work but raise quality standards and ensure installers don’t have to resort to desperate measures because they didn’t get it right first time.

This article appeared in the Contract Flooring Journal December edition


Stuart Bell - Managing Director Polyfoam XPS

Stuart Bell, Managing Director at Polyfoam XPS reflects on 2018 and talks of what’s in store for 2019.

Throughout 2018 we continued to see sector growth – although the bad weather at the beginning of the year stalled some roofing projects, the momentum soon picked up and we saw positive results overall.  

The insulation market has remained highly competitive and that has driven the development of new products to meet contractors’ changing demands. Within the last six months for example, we have launched six new XPS insulation board thicknesses in response to the need for more time and cost-efficient products.

We have also continued to work closely with contractors and specifiers to offer technical advice, including raising awareness about the risks of specification switching, which remains one of the biggest challenges for our sector.

Unfortunately, it is not uncommon for specified insulation to be switched during construction and after project-design stage compliance has been achieved. This is an issue which is leading to inaccurate U-values and potential non-compliance with Building Regulations. 

We hope that following the Hackitt Review, we will begin to see this trend shift in 2019. The recommendations in the report include more effective specification and an increased focus on how construction products are developed and tested. These measures would not only significantly raise quality standards, but drive the demand for accredited, independently-tested insulation products which are fit for purpose and ensure buildings perform to the required standards.

We also welcome the move by the Construction Products Association (CPA) to establish best practice marketing and technical information through its Marketing Integrity Group. This initiative could play a vital role in preventing ambiguous and misleading product information filtering into the market next year improving customer confidence and ultimately the quality of the built environment.

This commentary appeared in the December 2018 edition of Total Contractor


Rob Firman, technical and specification manager at Polyfoam XPS, addresses contractors’ queries about inverted roofs and extruded polystyrene insulation.

Why is a different lambda value used for an inverted roof calculation?

In simple terms, the ‘declared’ lambda value refers to the thermal conductivity of the product when it leaves the factory.

When laid over the waterproofing in an inverted roof, the insulation’s efficiency can be affected by rainwater draining between the boards. The declared lambda value is adjusted and the insulation assigned a ‘design lambda’ value, which is used in U-value calculations for inverted roofs. 

What is a water control layer?

The cooling effect of moisture reaching the waterproofed roof deck affects a roof’s thermal performance, so a water control layer is laid over the insulation to reduce the amount of moisture that can enter the build-up.

Water control layers, such as Polyfoam Slimline Zero, are membranes resistant to rot and UV decay, and impermeable to liquid but permeable to water vapour. They allow a favourable drainage factor to be adopted in calculations. The lower the drainage factor, the thinner the insulation required to achieve a particular U-value.

What coverings should be used above the insulation?

As the insulation and water control layer are loose laid on an inverted roof, rather than mechanically or adhesively fixed, a ballast is required to stop them being lost to the wind and prevent flotation after heavy rain.

A variety of roof coverings can be used, including green roofs and timber decking. The following roof coverings, however, are accepted as achieving the necessary fire performance without the need for further testing, and therefore are most commonly specified and installed:

  • Loose laid gravel at least 50mm thick, or with a mass greater than 80 kg/m2 (subject to maximum and minimum aggregate sizes).
  • A sand/cement screed at least 30mm thick.
  • Cast stone or mineral slabs at least 40mm thick.

Why do I need to know the site location before requesting a U-value calculation?

The average rate of rainfall during the heating season, based on location-specific data from the Met Office, is included in a U-value calculation. It is used to help calculate the amount of rain water the insulation is likely to be exposed to and the effect it could have on performance.

For example, a building located in East Anglia is likely to be exposed to significantly less rainfall than one in Western Scotland. There can be wide variations in rainfall in specific regions too – the average rainfall for Manchester is lower than the North West as a whole, showing the benefit of using location data to improve the accuracy of the U-value calculation.

Why is drainage important?

Building Regulations and British Standards require roofs to drain properly. If water is allowed to pond, the roof can be exposed to issues such as greater loads than it was designed to accommodate, accumulation of unsightly silt and algae, and freeze-thaw cycles that place stress on roof coverings.

For inverted roofs, drainage should be provided at both the water control layer and waterproofing levels. Drainage outlets should be positioned at the low points of the roof, not just the roof edge. The low point on precast concrete decks, for example, is most likely at mid-span because of deflection due to the deck’s weight.

For further information or advice, please visit

This article first appeared in the October 2018 edition of Total Contractor magazine


Rob Firman, Technical and Specification Manager at Polyfoam XPS highlights the risks of inaccurate U-value calculations and need for a more rigorous approach during the specification process.

It’s an unfortunate truth that despite their importance, U-values and their calculation are not as well understood as they should be and that can lead to misleading calculations. As an insulation manufacturer, raising this issue can be tricky; any suggestion that calculations produced by others are unfair can sound like sour grapes.

However, accuracy and adherence to standards is an issue that cuts right to the heart of the built environment. U-values resulting from inaccurate calculations feed into energy assessment calculations (either SAP or SBEM, for domestic and non-domestic respectively) that are directly responsible for demonstrating compliance with building regulations.

In many cases, a miscalculation is the result of an honest mistake or lack of understanding, but alarmingly, there is also growing evidence that standards aren’t being adhered to.

Turning a blind eye

A scenario when this may occur is when the insulation specification is switched during construction and after project design stage compliance has been achieved. There is often an assumption that the new product will have the same declared thermal performance as the one it is replacing. The manufacturer will have to supply a calculation to prove this. If the result is not identical, difficult and costly remedial measures will be required to make up the shortfall in performance. Sadly, in an effort to avoid that time and expense, it is not unknown for a revised calculation to be issued that says the same as the original.

Calculation issues and errors

There are several important factors to consider in a U-value calculation, particularly for inverted roofs such as the building’s location, the effects of rainwater cooling and ensuring the product’s ‘design’ thermal conductivity is used.

There are additional variables, any of which could cause a difference in result between two apparently ‘correct’ versions. Specific issues we have encountered recently include:

Rounding up R-values: The thermal resistance (R-value) of a construction material is its thickness divided by its thermal conductivity. An extruded polystyrene (XPS) product with a conductivity of 0.034 W/mK, at 200mm thick, has an R-value of 5.88 m2K/W or 5.85 m2K/W if rounded down in accordance with BS EN 13164 to the nearest 0.05 m2K/W. We’ve seen examples of calculations where it has been rounded up, yet the R-value cannot be any higher than that without breaking the laws of physics.

Correct thermal values for airspaces: U-value calculation software allows the dimensions of an airspace to be entered to ensure the correct thermal resistance is used.

Where one, or both surfaces, either side of the airspace has a low emissivity, ISO 6946 includes a formula to work out an increased airspace thermal resistance. We have seen examples of calculations where a greater airspace resistance has been included, despite the surfaces either side being standard high emissivity surfaces. There has also been no justification as to why the higher resistance has been claimed in the airspace description.

Average UK rainfall figures: U-value calculations for inverted roofs account for the cooling effect of rainwater. The lower the rainfall, the lower the impact on the result. If the location of the building is known, rainfall data for that location, or one nearby, should be used (ISO 6946 refers to ‘data relevant for the location’). However, we have seen the UK’s average rainfall figure be used, even when the building’s location is known to have greater rainfall.

Raising standards: Misleading calculations call into question the construction industry’s ethics and values as well as its commitment to delivering a quality end product.

As a responsible manufacturer, transparent about the calculations we produce and willing to talk through the results with any customer, it’s frustrating to know that inaccurate calculations make their way into the marketplace.

Unfortunately, there is insufficient knowledge in the industry, especially regarding relevant standards, which makes it very difficult for this issue to be adequately policed. This is exacerbated by the fact that training in calculations isn’t up to scratch.

Initiatives like the BBA’s competency scheme for the calculation of U-values are supported by a minority of insulation manufacturers and companies, but not enough to really put the spotlight on accuracy and competency.

A rigorous approach: Until this situation changes, we call on the specifiers and purchasers in the construction industry to join us in being more vocal about raising standards.

Test the manufacturers you work with. Obtain more than one calculation for the projects you are specifying and compare and question the results.

Seek clarity and be confident that a manufacturer does not simply sell you thinnest solution with the biggest margin, but a product with an accurate U-value which will ensure a building – and our industry – performs to the highest standard.

This article first appeared in the November 2018 edition of ABC&D magazine