Insulation materials - introduction
Key issues
• Reducing the amount of energy used from fossil fuels is the most important factor in promoting sustainability.
• Insulation has the greatest potential for reducing CO2 emissions.
• Energy conserved through insulation use far outweighs the energy used in its manufacture. Only when a building achieves a ‘LowHeat’ standard does insulation’s embodied energy become significant.
Performance
The most important aspect of an insulation material is its performance – that it consistently provides the designed-for resistance to the passage of heat throughout the lifetime of the building. Though the insulation manufacturer’s published performance expectations will be an essential guide, other factors associated with the ‘real-life’ installation of the material need to be considered as part of the design process:
• Ease of installation – the ultimate performance will be determined by how effectively a builder can install a material using conventional skills. For example, insulation slabs need to be installed so that no gaps result either between adjoining slabs, or between the slabs and other construction components that form part of the overall insulation envelope, such as rafters or joists. Any gaps left over will enable the passage of air and result in a reduction in performance.
• Shrinkage, compaction, settlement – Some materials are likely to suffer a degree of dimensional instability during their installed life. In many instances this is anticipated and can be overcome through careful design and installation methods. In all other instances, the specifier should seek guidance concerning associated risks from the insulation manufacturer – particularly where materials have not had an established record of installed performance.
• Protection against moisture – some insulation materials will suffer a degradation of performance when moist or wet. The designer should, through careful detailing, ensure that vulnerable insulation is protected from moisture. If moisture is a high risk (ingress or over 95% RH), then a suitably resistant material should be specified.
(Illustration courtesy of the Architects Journal)
Environmental impact
• As the ‘green agenda’ has become more absorbed into the popular consciousness, so too has the awareness of the environmental impact of the materials used in construction. This impact has become the subject of government guidance in recent years – notably with the introduction of the Code for Sustainable Homes and its integral association with the BRE’s ‘Green Guide to Specification’ which rates building materials according to their overall impact on the environment. Consequently, competition between product manufacturers to occupy the environmental ‘high ground’ has become fierce. This is particularly apparent within the insulation sector where claims and counter-claims are being exchanged between manufacturers of competing products to an unparalleled degree. The result is a state-of-affairs where ‘Greenwash’ stands to obscure impartial data and opinion. Steering a course through this blizzard of ‘information’ has become something of a challenge for the specifier looking to achieve an insulation performance with the least environmental impact.
• There is no doubt that some insulation materials have a more notable environmental impact during their life cycle than others. Life Cycle Assessment (LCA) is an evolving discipline that can be used to provide an appraisal of a material’s impact from the point of raw material extraction, the manufacturing process, its use within a building, through to its final disposal (cradle to grave). Ideally, each material would be accompanied by an LCA with each assessment produced in an identical manner. In reality, this is nowhere near the case.
• LCAs results can vary by even more than 100% for the same product, depending on the system boundaries set (what has or has not been included), the emission factor databases used and the assumptions made. Though the ISO standard for LCAs (14040) includes guidance for assumptions and allocations, it was developed to outline good practice in preparing LCAs, not to give exact details as to what should be included in a study or what secondary data should be used. As such, many ISO 14040 style LCAs are produced as comparative studies with the figures presented for two or more products valid in their own context. However they cannot be compared with other LCA results without considerable effort to understand how each figure was derived.
• The PAS 2050 standard on carbon footprints is much more strict and details how to set system boundaries and many assumptions but still allows relatively large differences in results to occur stemming from the choice of emission factors used. It is likely that in the long-term, LCAs will become more standardised regarding all the variables or at least in terms of transparent reporting. But in the short term, product specifiers should continue to be very cautious when comparing LCAs from different sources. This is particularly true for LCAs of agricultural and forestry derived products, where factors such as soil carbon losses are often over estimated or not included - causing a great deal of potential variation as is the relevance of older LCAs due to the rate of change and scale up often associated with “new” products.
• Below we have tried to provide an account of the key environmental impacts and performance issues associated with the most important insulation materials available in the UK. Where possible, LCAs have been studied, but where no LCAs are available, we have had to depend on the often more unreliable data published by manufacturers and trade associations – who obviously have vested interests. It is important to stress, therefore, that the specifier should consult directly with the manufacturer before selecting a product.
Embodied energy
• Embodied energy figures are produced in the same way as other environmental impact categories as part of an LCA and so the same caution should be applied to comparisons of figures from different sources.
• Though the ‘embodied energy’ of insulation materials is arguably important, the energy used to create and transport materials should be considered in the more important wider context: Most of the energy a building consumes during its lifetime is ‘operational/functional energy’ including such as that is required to heat space, heat water or power appliances. An insulation material should be first considered for its thermal performance and, unless other contextual factors apply, only subsequently for its environmental impact.
• Embodied energy becomes important only when high levels of operational energy efficiency have been achieved (eg through Passivhaus and Code Levels 4, 5 & 6). In these instances embodied energy can increase to around 10% of overall energy expenditure.
• Embodied energy values are usually expressed
in energy used per kilogram - but for any useful comparison to be made
between materials, thermal performance and material density need to
be included. Thus for example, based on rough assumptions, for 1 m2
of surface to attain a u-value of 0.2 W/m2 K, the energy required would
be (thickness of material x material density x embodied energy value):
Cellulose – 46 MJ
Sheeps wool – 100 MJ
Polyurethane – 424 MJ
Wet-formed wood fibre-board – 546 MJ
• It should also be noted that some software and databases will report embodied energy figures as a Lower Heating Value (LHV). This LHV assumes that the latent heat of water vaporised from the fuel and reaction products is not recovered. The LHV in general is less than 10% lower than those of Higher Heating Value (HHV) figures but this varies with each fuel used. It is often not mentioned which figure is calculated; however, where it is know it is stated below.
• It is not unusual to find significant discrepancies in the values described in available literature, both by academics and manufacturers, for identical materials. Though we have tried to be as accurate as possible when quoting values for embodied energy and thermal conductivity, these values should be considered with a degree of caution. In all cases, values should be confirmed with individual manufacturers.
Types of insulation
There is a potentially bewildering array of insulating materials for the specifier to select from. They range from the familiar polystyrene and mineral wool through to alternatives gradually establishing themselves in the market such as sheeps wool and hemp. In an attempt to give some semblance of order to the array, we have grouped insulation materials according to provenance:
 |
Plant / animal derived insulation |
 |
Mineral insulation |
 |
Oil-derived insulation |
When selecting an insulation material, primacy should be given to performance in the construction context. Very few insulation materials are capable of performing all the functions called for eg sheeps wool is perfectly suitable for ventilated wall construction but not in unventilated cavities. The choice of insulation is intrinsic to the choice of construction.
Procuring informationPutting together information on the environmental impact of building materials, and in particular insulation materials, is notoriously difficult. The most reliable source of information is that derived from an LCA, either generic or product-specific, carried out by an independent party and publicly funded. Other more common LCAs are those published by manufacturers and other industry bodies – though of considerable interest, the researcher will be sensitive to conflict of interest. A perhaps understandable, but unfortunate tendancy of many publishers
of LCAs, is their proclivity to only publish headline findings
whilst carefully guarding the supporting data (eg BRE’s
Green Guide ratings). This obscurism prevents peer review of evidence
and can only lead to doubt concerning the findings. Obtaining information directly from manufacturers is only moderately successful. Enquiries are met variously by helpfulness, evasiveness, non-cooperation through to overt hostility. |
