Natural Insulation Vs. Manufactured Vs Embodied Energy

Insulation is a fundamental component of any energy efficient and sustainable building. Most now agree that the 'energy saving poten­tial' of insulation, measured over the lifetime of a building, should be the dominant factor in its specification. In fact, the lifetime differences between various insulation products are small. The most important factor of all is to ensure that the insulation is correctly installed. Over the past few years choosing an eco-­friendly insulation material was quite simple. All you needed to do was select one that did not use CFC or HCFC blowing agents in its manu­facture. However, with the successful phase-out of ozone destroying gasses by EU law (based on the Montreal Protocol) it became a less clear-cut decision.

So how can we choose the most environ­mentally sustainable insulation to use in our buildings? Many might argue that 'natural is best' but others counter with 'natural cannot promise durability'. It is true that some insula­tion applications are accessible enough for us to replace them occasionally throughout the lifetime of the building if we so wish but, likewise, some application decisions are 'whole building life' choices. Let's take a look at some of the environmental issues that may apply to building insulation.

Embodied impact - does it matter?

For a number of years now, insulation materials, among many others, have been compared on the basis of embodied energy (the energy used to build the construction elements). However, if energy saving is high on your agenda, I believe that it is the balance of the embodied energy against the 'in-use' energy consumption over the lifetime of a building that is more impor­tant. Indeed, due to the fact that insulation, by its very nature, is there to save energy, it has become widely accepted that the embodied energy of any insulation material is insignificant compared with the energy saved by it over the lifetime of the building in which it is installed.

However this should not allow us to become compla­cent. The above statement will only hold true whilst we continue to design buildings with quite high levels of energy consumption. All this will change if and when our buildings have low or zero heating/ CO2 emission requirements. This can only be achieved by using insulation wisely at appropriate thicknesses and by detailing our buildings properly to ensure airtightness. Only when our buildings get to low or zero heating levels will the embodied energy of the insula­tion choice become significant enough to worry about.

One measure of embodied impact is the rating system used in the BRE's Green Guide to Building Specifications. This publication rates products from A+ to E on a basket of environmental impacts, including embodied energy. These ratings are based on generic life cycle assessment (LCA) data. You will find that almost all insulation materials, for which data is given, get the top ratings of A+ or A. The common exceptions are cellular glass, extruded polysty­rene and high-density (128 kg/m3 and higher) rock mineral fibre; this is a clear reflection of the fact that the embodied impact of insulation materials is relatively insignificant. However, it does illustrate that it is important to consider the density of the insulation material, as more dense insulants may have a low embodied impact per kilogram, but not per m3 or m2.

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How in-use energy is far more significant than embodied energy

Interestingly when the impacts for insulation are combined with the impacts of other materials that make up, say, a wall or a roof, the different ratings of insulation products become largely irrelevant as they are masked by the impacts of the other materials in the construction. In the guide it is perfectly possible for a wall insulated, with extruded polystyrene, to get an overall A+ rating, even if the insulation itself does not, (some might argue that this is a failure of the rating system used). It is equally possible for a wall insulated with an A rated insulation material to get an overall E rating because it is the rating for the whole construc­tion that counts as far as the Green Guide data is concerned. Accurate and unbiased embodied energy / embodied impact figures for insula­tion materials are difficult to find, other than in BRE's life cycle analysis (LCA), and therefore should be treated with care.

In-use performance

It is widely accepted that reducing "in use' energy consumption of buildings is the key to their environmental sustainability. Therefore, the major parameter on which to compare insu­lation materials must be their ability to deliver their specified thermal performance over the lifetime of a building. This is one of the key themes of an independently produced report on the sustainability of insulation materials, funded by BING (the European trade asso­ciation for manufacturers of rigid urethane insulation products), which brought to bear the concept of risk factors. These are all factors which could detrimentally affect the thermal performance of individual insulation materials, sometimes in very different ways, and hence the environmental sustainability of buildings. These risk factors may include the impacts of:

• liquid water or water vapour

• air-infiltration

• compression or settling.

On the whole it will be poor site work that will allow these risk factors to come into play. On-site installation practices are notoriously uncontrollable and all materials will perform badly if installed without due care and atten­tion. However, for some insulation materials the problem may stem from what is claimed for the product in the first place.

Adherence to common rules for thermal performance claims should be checked. The EU Construction Products Directive has created a set of harmonised product standards for insulation which demand that the thermal performance of all products is quoted in a comparable way that takes account of ageing and statistical variation. It is called the Lambda 90:90 method. All major UK insulation manufac­turers have adopted this approach to quoting thermal performance. It is worth noting that the introduction of the harmonised product standards added about 10% to the thermal conductivity of the insulation products that are covered (i.e. made them 10% worse). However, at the present time there are a number of smaller scale products for which there is no harmonised standard available and therefore no consistent method that takes account of statis­tical variation. No doubt these will be brought into the fold soon but, until then, inconsistency will reign. One particular case in point is that of multi-foil insulation.

Once the global issues have been consid­ered it is then time to consider less pressing, but still important, issues such as recycled content, local sourcing, disposability etc. The key to the environmental sustainability of any product is a balance of all these issues. Taking just one issue and over-focussing on it could be counter-productive.

Recycled content of products is going through something of a revolution in the UK construction industry. The Government has funded a body called The Waste & Resources Action Program (WRAP) to promote materi­als that have a recycled content. It gives very specific rules as to what counts as recycled content and what does not. These rules follow the definition cited in the ISO standard on Environmental Labels and Declarations>.

Some insulation already contains recycled content. However, when examining the recycled content of insulation materials please bear in mind that recycled content is the proportion, by mass, of recycled material in the product. Only pre-consumer and post-consumer materi­als should be considered as recycled content." This means that surplus material cut from the edges of products during their manufacture and shredded and added back in at the start of the process don't count.

Another, often overlooked aspect of the performance of insulation materials is their performance with respect to fire. This is quite a complicated area but, roughly speaking, there are two facets to consider: reaction to fire and fire resistance. Reaction to fire is measured by the 'Class 0' type rating system enshrined in Approved Document B to the Building Regulations in England & Wales or the risk categories shown in the Technical Handbooks in Scotland. These ratings can be achieved by reference to the new Euroclass system for reaction to fire or by the tried and tested BS 476 Parts 6 and 7.

There is a debate in the insulation industry, at present, as to which route is best. What has caused this confusion is the fact that the new Euroclass rating system for reaction to fire is irrelevant when applied to 'naked' insulation products, as the system was developed for wall and ceiling linings and insulation is rarely used as such. The reaction to fire test has slightly more value when used for products tested 'in application', since insulation products are then tested mounted as they would be in practice for example behind plasterboard. '

Proponents of the Euroclass system suggest that 'naked' products lie around bUilding sites all the time and that the products are expOsed when, say, holes are cut in walls, but I cannot understand how testing a product as a wall or ceiling lining can relate to packs of products lying on the ground. Regardless, the test still gives no indication of a product's ability to resist fire. It is this crucial distinction that

can make all the difference to the ability of a building to withstand a fire and maintain struc­tural integrity long enough to enable occupants to leave safely, and allow emergency services more time to get the blaze under control and salvage the building. Mistakenly choosing a material based on its reaction to fire, without taking into account its resistance to fire, may therefore at best be costly, and could at worst prove fatal.

The crux of the issue is that some materi­als have excellent fire resistance qualities but relatively poor reaction to fire ratings, whereas others have the best reaction to fire ratings but relatively poor fire resistance properties.

What about the Code for Sustainable Homes?

There are a number of different insulation mate­rials that, if installed correctly, can meet the low energy requirements of the higher levels of the Code for Sustainable Homes (CSH) - introduced in Chapter 2. For example, the thickness of insulation required, and whether this impinges on useable space, needs to be considered.

But having excellent levels of insulation is not enough - it is vital to also consider the overall impact of the materials used, and their effec­tiveness over the lifetime of the building. In the past the environmental sustainability of insula­tion materials has been compared on the basis of embodied energy. However, this may not deliver a true picture of environmental impact and it is now recognised that a much wider range of issues needs to be considered, not just embodied energy.

Insulation considerations

LCA techniques provide a good, holistic tool to achieve this but it is also important to look at the whole construction and not just one component of it. The CSH has endorsed this approach by awarding credits based on the BRE Green Guide ratings for the roof, external walls, internal walls floor and windows of a house construction which are themselves based on LCA analysis. If all 5 elements achieve an A rating then just 2.7 credits are awarded if they all get an A+ then a maximum 4.5 credits can be awarded.

It is also important to recognise that it is operational energy use that creates the vast majority of environmental impact, and this too has been reflected in the CSH in the balance of credits allowed for reduced CO2 emissions versus those allowed for materials: 17.6 and 4.5 discretionary credits respectively. However, there is one vital aspect of environmentally sustainable buildings which is not addressed by the CSH, and that is the point that the longevity of the standards of operational performance is critical.

For example, the performance of some insulants, such as rock mineral fibre, can dete­riorate rapidly if exposed to water penetration, moving air penetration or compression. This may increase operational energy use and hence compromise the environmental sustainability of the finished building to an alarming degree. Other insulation materials, such as rigid phenolic and rigid urethane insulation, are not vulnerable to any of these problems. The question of longevity is particularly important in the light of the requirement for energy performance certificates for all houses. These certificates are an important part of the resale or let process, tracking the energy performance of homes over time.

So when it comes to achieving the best standards, and meeting some of the key objec­tives behind the CSH whilst still delivering reliable long term performance, there are three important considerations: in the first place, work to the lowest possible U-value regardless of insulation type, design out the risk of the chosen insulant not performing as specified, and, if you can't, choose an insulant that is at low risk of failure.

In this way the industry knows that it can deliver housing that meets the increasingly tough criteria for carbon dioxide emissions, without having to rely on expensive technology or worry about site restrictions. In other words, a smart solution that keeps the numbers of new projects and higher standards within the realm of both the achievable and the realistic.