Energy efficiency:reflective insulation

Highly reflective

23 January 2017

Martin Oxley charts the rise of reflective insulation


After running 26.2 miles and receiving your well-earned finisher’s medal, you are usually also given a goody bag on completing your marathon. Along with the T-shirt, snack and muscle-relieving pain gel, you will find a shiny, highly reflective space blanket. This helps to keep you warm after you have stopped running – so why not use the same technology to keep your house warm as well?

Testing performance

When the first reflective insulation products hit the shelves of builder’s merchants many years ago there was limited certified testing, so some of their original performance claims might have been a little optimistic. Testing houses in both the UK and Europe also achieved varying results after analysing the products in the same way as they normally would traditional insulants.

So, while test houses and manufacturers agreed on a standard testing methodology for thermal performance – a process that took several years – some companies opted for in-situ evaluation.

It soon became apparent that it was extremely difficult to build ‘standard houses’ repeatedly and ensure that thermal performance and weathering conditions remained absolutely identical, so as to evaluate the true performance of these new reflective insulants with complete accuracy. This caused market confusion and led to many architects, specifiers and contractors not selecting reflective insulation for their projects.

Thermal standard

After several rounds of evaluation with some of the best insulation-testing houses, Europe agreed on a thermal performance standard in 2012, BS EN 16012:2012+A1:2015 Thermal insulation for buildings – Reflective insulation products – Determination of the declared thermal performance.

There was now a defined methodology for direct thermal comparison of reflective insulants. This, together with the emergence of the first reflective insulation certificates from the British Board of Agrément (BBA) more than 16 years ago, increased the credibility of the industry and provided consumers with the reassurance they required, and sales started to increase significantly during this period.

Radiation of heat

All insulation products work by reducing heat flow, which occurs in one or more of three ways – conduction, convection or radiation – with heat always moving from the hot to the cold side.

Reflective insulation’s key feature is, of course, to limit heat flow by radiation. The radiated energy is invisible and causes no rise in temperature until it hits a surface, where it is absorbed and causes the object to get warmer. For instance, radiative energy from the sun will pass through double-glazing, but once it hits an object inside the conservatory it starts to heat it up.

When comparing the performance of reflective insulations, a key technical characteristic to consider is the emittance of the product, more usually described as emissivity – specifically, a surface measurement of the product’s ability to emit radiant energy.

Emissivity is a ratio, and is given a value between zero and one. Zero indicates that all the energy is reflected and none is absorbed, as for example with a highly polished silver surface. Conversely, a value of one denotes that none of the energy is reflected and is entirely absorbed, as by a totally black body such as a black hole in space.

For a typical reflective insulation product, the aluminium foil outer surface would have a declared ‘aged’ emissivity of around 0.05, meaning that the significant majority of energy is not absorbed; it is ‘aged’ because it should represent how the product will perform after many years, rather than just initially. Conversely, for a typical brown housebrick, you would usually expect an emissivity value of around 0.90 – that is, most of the energy is absorbed.

Because emissivity is a ratio of the energy received and reflected, then the temperature and direction of measurement is an important function. Emissivity therefore needs to be measured accurately; the texture of the sample can also have an effect on the true result by scattering the light.

BS EN 16012:2012 + A1:2015 refers to BS EN 15976:2011 Flexible sheets for waterproofing – Determination of emissivity, which provides details of testing and reporting methodology.

With most reflective insulations, you are determining very low emissivity values and are working at the limits of the instrumentation, so using an experienced independent testing laboratory such as the BBA is essential in order to obtain accurate, precise and credible results. The results supplied should be ‘aged’, to take into account the material’s ability to resist oxidation or corrosion.

insulation

Figure 1: Pitched roof application

A harmonised European Product Standard is currently being developed for reflective insulation, which is due to be published shortly. Once officially issued, manufacturers will then be able to CE-mark their product to encourage increased sales across the continent.

BBA anniversary

The BBA celebrates its 50th anniversary in 2016, which means we have been evaluating numerous insulation types – from novel to traditional, in many different applications – for half a century. Each certificate has a scope of use that lists what the product is, its technical performance, how it complies with Building Regulations and where it can be used.

Insulation manufacturers work hard to produce the best product for each specific application, to ensure that all the necessary requirements are met. Obviously, for any insulation the key element is thermal performance, so correct installation is absolutely essential.

Correct installation of insulation was one of the many parameters picked up in the Zero Carbon Hub Performance Gap report as an area to improve (see Closing the gap). Architects, designers and specifiers are required to take CPD so as to keep abreast of developments.

However, an installer may often only attend a one-day training course and become approved with typically very little follow-up or auditing, even though they may then be regarded as the company’s expert.

So the focus for manufacturers wanting to increase market share must be to prepare comprehensive technical literature complementing the sales material, as well as detailed installation guidance to demonstrate the ease of fitting and all the key features and benefits.

This guidance could range from easy-to-follow images of the installation process right through to on-site training schemes. Companies are keen to ensure that their product is installed correctly, does what it should do and stands the test of time.

The BBA’s auditing and inspection team has a wealth of knowledge and experience of the range of on-site insulation, from the best to the worst, so it can offer a valuable resource for those looking to ensure that the product is installed correctly.

Market share

Given that reflective insulation works according to the standard principles of physics and was used as early as the space race of the 1950s and 1960s, being both thin and lightweight, then you could ask why it has not been used in more applications.

The use of reflective insulation in conjunction with other traditional insulants can help achieve increasingly stringent U-value targets. To ensure maximum performance, products must be used together with an air cavity in front of, and in some cases behind, the insulation.

The lack of a current European Product Standard may be one of the reasons why architects, specifiers and contractors continue to use their normal insulant, given that this will have worked in the past and they do not have time to investigate all the possibilities. But this is where a BBA certificate can enable the manufacturer to address many of the questions that the industry has in relation to product performance.

The use of reflective insulation in conjunction with other traditional insulants can help achieve increasingly stringent U-value targets. To ensure maximum performance, products must be used together with an air cavity in front of, and in some cases behind, the insulation.

Some products are also classed as a vapour-control layer because they offer a high degree of moisture resistance and, of course, must be used on the warm side of any proposed system to reduce the risk of any interstitial condensation.

Others are classed as breathable because they are perforated through all layers to allow any moisture build-up to pass through the material and dissipate on the other side, typically in the form of a ventilated cavity in a warm pitched roof.

So although it may have not have been a smooth or easy ride to get here, reflective insulation is now definitely making significant inroads into the European insulant market.

Martin Oxley is a project manager at BBA

Further information

  • Image © TLX Insulation
  • This feature is taken from the RICS Building control journal (November/December 2016)