The great multi-foil debate continues
publication date: Jul 17, 2008
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author/source: David Harris
Multi-foil insulation has been manufactured and installed for over 25 years, but really hit the headlines in August 2006 following the issuing of a technical guidance note by LABC entitled Use of Multi-foil Insulation Products: Compliance with Regulation 7 and Requirement L1. This stated that: “The LABC technical working group feel the 2006 changes made to Part L of the Building Regulations are sufficient to warrant a re-evaluation of the acceptability of multi-foil insulation products.” It went on the recommend that only insulation with proven performance to test values obtained in accordance with paragraph 3.10.2 of BR 443 should be used hence forward.
This was strenuously lobbied against by various multi-foil manufacturers, including those represented by the Confederation of Multi- Layer Foil Manufacturers (CMM). Their contention was that the problem arose from attempts to compare very different materials and technologies using common ways of testing and evaluation.
The issue went to the Queen's Bench Division Administrative Court, which ruled that the changes made to the document BR443 in Part L of the Building Regulations which affected multifoil insulation were unsafe.
However, that judgement did little to clarify the situation. Multi-foil insulation manufacturers kept stressing the in-situ performance claims for their products, while various opposing parties, including the manufacturers of rigid foam and mineral wool insulants, rubbished these claims.
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What is multi-foil insulation?
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Multi-foil insulation products comprise a series of extremely thin low emissivity, metallic or metalised films interlayered with low thermal conductivity wadding, or foam of various types. The various layers are then welded, glued or, more usually, sewn together to form an insulating blanket. They are supplied in rolls or folded sheets and are primarily used in the refurbishment of residential roofs because they can be installed very simply with minimum loss of usable space. This is important in a project like a mid-terrace loft conversion where raising the roof height is not an option. |
LABC has kept a watching brief, but decided in April 2008 that the uncertainty had gone on too long. In an attempt to move things forward, the body issued a further Technical Guidance Note called “Use of Multi-foil insulation products: Compliance with Regulation 7 and Requirement L1” . This considers the in-situ tests used by multifoil manufacturers to underline their performance claims and concludes: “Such tests set out to demonstrate that the actual energy consumption of buildings using multi-foil insulation will be equivalent to (or better than) an identical building using mineral wool insulation, and having done so, claim the same “R” value for the multi-foil product as would be accepted for the test thickness of mineral wool. There is currently no accepted national, European or international standard for performing tests in this way, but work is underway in Europe to examine the viability of such testing methods.”
The LABC statement continues: “Members should be aware that Circular 06/2007 issued by DCLG after the Judicial Review judgement was released states that ‘The Department is currently of the view … that comparative testing does not provide accurate indications of thermal performance.’ Siting tests carried out by the National Physical Laboratory, the LABC notes continues: “Multi-foil manufacturers who have used the comparative testing route are claiming the insulating properties of their product to be approximately three times better than can be verified using existing national, European or international test standards.”
Referring to the earlier judicial review, the LABC note states: “The specific link to paragraph 3.10.2 of BR 443 has now been removed as a result of the Judicial review, but this was because the Judge felt that the proper notification process to the EU had not been followed. It is important to note that the Judge did not make any judgment whatsoever on the merits of any of technical issues involved in the case.”
“The Judicial review does not therefore significantly change or clarify the technical issues surrounding the use of multi-foils in any way,” concludes LABC.
“Unfortunately LABC have become aware of claims now being made by some multi-foil manufacturers that the judgment requires Building Control Bodies to accept Certification based on comparative testing as a valid means of demonstrating compliance with the Building Regulations. This is not the case, and Building Control Bodies remain entitled to make their own judgement about compliance with the regulations, based on their assessment of any information they consider relevant.”
The note continues that the LABC would consider “the use of any multi-foil product which has an Agrément Board Certificate to be acceptable, providing it is used strictly in the manner set out in the certificate.
“The LABC conclusion resonates with the BBA’s own findings during its assessments of multi-foils,” explains Alan Thomas, Sales and Marketing Director, British Board of Agrément. “We have yet to see one that can achieve a 0.2 U-Value as a single layer, even when we have been testing (as a separate exercise) non-BBA-approved material bought on the open market on our UKAS-accredited test equipment. We are working on a pan-industry study on real-life installations using a variety of insulation materials to see how these perform.
We have support for this from the NHBC and BRE, but this is a longterm project and we encourage specifiers working in today’s market to choose products whose performance can be proven through established tests and approvals provided out by bodies accredited by UKAS for thermal testing work.”
According to Tim Woodbridge, Chairman of Web Dynamics: “The LABC’s decision to issue a new guidance note finally brings clarity to the industry over the use of multi-foils. The guidance note … strongly recommends the use of BBA certified multi-foils and advises that they should be used as part of an insulation system, and not as a single layer, in order to meet the normal roof U-value requirement of 0.2. Web Dynamics' customers will be aware that this is an argument that the company has advocated for almost two years and the guidance supports our view about the importance of using multi-foils with a further layer of insulation.”
“The rising cost of energy is having the two-fold effect of forcing up the price of both insulation products and heating bills,” continues Woodbridge. “The way multi-foils are constructed makes them less sensitive to fluctuations in raw material and energy costs than traditional insulants. At the same time multi-foils reflect more than 80% of radiant heat loss and stop air leakage. Put simply, multi-foils as a partner for PIR and glass wool are here to stay for the simple reason that they are a cheaper way of installing insulation and saving on energy bills.”
KdB Isolation has a somewhat different position.
“The key difference between conventional insulation and reflective insulation is the low emissivity of external surfaces. Low emissivity means high reflection of the infra-red thermal radiations. This key characteristic has two consequences. In winter conditions, it means when the heat energy flows from inside to outside with a difference in temperature of average 15°C, unventilated air gaps surrounding the reflective insulation have an increased thermal resistance. The thermal resistance of the system (Reflective insulation + 2 unventilated air gaps) can be accurately measured with a guarded hot box without any doubt concerning the heat losses through convection, conduction nor radiation. KdB Insulation has chosen the best laboratories in Europe to perform those measurements in conformity with National and international standards.”
“But, in some particular conditions, when the heat energy flows from outside to inside and when the difference in temperature are important between the two sides of the roof for example, then convection effects can occur, deviating an important percentage of the incoming heat energy. In such conditions, more sophisticated models of calculation have to be used to simulate the behaviour of the reflective insulation products. The tightness of Airflex also is of great influence on the insulation effectiveness. The combination of tight/reflective insulation and permeable insulation is recognised by experts as one of the best system ever developed for every type of climate.”
The rigid foam manufacturers’ association, BRUFMA, has welcomed the LABC’s Technical Guidance Note. John Roberts, Chief Executive, said: “The benefits of using a superior thermal insulation, such as PUR/PIR, are wide-ranging and extremely valuable.
Improved energy efficiency has very positive effects on the environment in terms of reduced greenhouse gas emissions, whilst also providing consumers with lower energy bills. The use of insulation materials with misleading thermal performance claims has far reaching implications in both environmental and financial terms. Use of PUR/PIR insulation allows a lower thickness of insulation to be used to meet standards and regulations whilst allowing maximum use of space available. As well as space-saving, the lower thickness of insulation products combined with the lightweight nature of PUR/PIR insulation products improves ease of handling, speeds up construction time, enhances safety and reduces transport costs.”
So, the debate continues. There is currently no accepted national, European or international standard for performing the kind of in-situ tests championed by the multi-foil manufacturers and alluded to in the LABC’s note. Work is underway in Europe to examine the viability of such testing methods, and new methodologies and standards may eventually emerge as a result. In the meantime, confusion reigns. Some of the larger players in the multi-foil sector seem to be keeping their powder dry for battles ahead, while others have taken the pragmatic stance of seeking BBA certificates and promoting multi-foils as one component of an insulation system. Meanwhile, the UK construction industry still waits for a definitive answer on multi-foils’ performance.
