In this exclusive extract from Environmental Construction Handbook we introduce environmental assessment methods for buildings.
It seems at first that there are nearly as many methods of assessing a building as there are ways of defining sustainability or ways of constructing the building in the first place. The number of assessment tools is growing fast, as architects and other building consultants each devise a system which best suits their needs. The one thing they all have in common is that they measure the performance for a number of indicators, such as the sustainability indicators issued by the government, against benchmarks.
With any assessment, the answer you get depends very much on how you ask the question. Any scientist will tell you that the results of an experiment can be meaningless – an artefact of the methodology used – if it is not devised properly. So too, eco-labelling can be merely 'greenwash', misleading or, at worst, factually inaccurate.
One eco-labelling scheme that has been successful is the EU energy label that must be displayed on all new domestic white goods and light bulbs. Part of the reason for the success of the EU scheme is that it compares relatively few variables for products that have the same basic purpose and then presents the results in a way that is easy to 'read'. Despite this, even though buildings vary enormously in size, function and construction, it can be possible to give them a single rating – as is done with BREEAM, EcoHomes, LEED – and for the result to be meaningful.
Assessments can vary from simple checklists, or rankings of construction materials, through to sophisticated models. However, more complicated need not necessarily be better. A number of factors determine which assessment or tool is the most appropriate for a project:
- indicators considered
- the inputs the methodology uses
- the outputs (the type of results)
- the creator of the methodology
- who the assessor is to be
- the scope of the assessment
- the building type it is intended for.
The amount of information that is available about a project will depend largely on the design stage.
Early design stages
Early in the design process, assessments are more akin to tools to optimise the design of the building, to aid in the selection of sustainable materials and to minimise the use of energy or water.
Early design tools may be self-consistent but meaningless for the absolute judgement of the resulting building. For example, the LT Method is useful for evaluating the relative performance of a number of design solutions for a proposed building, with differing floor plans, orientations and façade penetration. It is not intended to provide an accurate prediction of the actual energy use in operation.
Late design stage, or completed building
Assessments conducted on late designs, or completed buildings position the building within the lexicon of building practice. In general, they require much more detailed information in order to complete the assessment, even if the result of the assessment is a single rating, such as EcoHomes or the Australian Nationwide House Energy Rating Scheme (NatHERS). In order to give designers guidelines as to how to meet the requirements of the assessment a cut-down version of the assessment, or a checklist, may be issued as a design tool, as in the case of the NatHERS and the French ESCALE assessment.
Whether the results from an assessment are going to be useful depends very much on who is going to use the results: building professionals, large client organisations, home owners or building managers.
For example, the 'My Home' online home energy check from the Energy Saving Trust could help a homeowner who wants to improve the energy efficiency of their home but who doesn't know where to start. However, it would be completely inappropriate for a housing association which, from April 2003, has been required to use the BRE EcoHomes assessment and achieve at least a 'pass' (if it builds grant-funded social housing). (The Housing Corporation increased the requirement to a 'very good' rating in 2006. )
A number of assessment methods have been tailored by their creators in relation to the conditions found in specific countries or regions. Climates and economic conditions vary considerably around the globe and can have huge effects on a building's performance – one reason for the different emissions targets for different countries under the Kyoto protocol.
Just as there is disagreement among the international community about how best to tackle global environmental problems, so there is a variety of opinions about how to improve the sustainability of buildings, ranging from enthusiasm that borders on green-fundamentalism through to near apathy, and even antipathy. Protecting the environment has often been opposed on the grounds of possible harm to the economy, although this needn't be the case. Superimposed on this there is a 'technical' vs 'vernacular' standoff. Some are 'wild about technology...' while others advocate living a more 'natural' lifestyle, building mainly with reclaimed materials such as tin cans and vehicle tyres with minimally controlled building services.
Though these differing viewpoints of sustainable construction aren't automatically at odds with the Brundtland definition of sustainable development, they are somewhat at odds with each other. This is important where weightings are applied to the relative relevance of data in an assessment.
Early design stage tools or assessments are usually used by the building's designers. Some tools which have the advantage of being easy to use, have in-built data and assumptions that are hidden to the architect or engineer. The immediacy of the results may consequently be undermined by their simplification.
For completed designs and buildings, assessments often need to be completed by an accredited assessor, who may or may not be part of the design team. This is partly a quality assurance step – particularly necessary when the assessment is required for regulatory purposes, as in the case of the SAP which may be used to show Building Regulations compliance – and partly to protect the intellectual property of the creators of the assessment.
The assessment may deal only with building components or systems (in which case it is likely to be used mostly in early design stages), with whole buildings or sometimes with whole developments and urban environments. Arup's SPeAR™ tool is one assessment that can deal with these.
It is well known that some materials are more desirable in environmental terms than others. Various methods of comparison have been proposed to circumnavigate the shark-infested waters of manufacturers' information. The two main types of assessment are measurements of embodied energy and life-cycle analysis (LCA). There are also a number of websites and books offering advice on materials selection, and which either do not neatly fall into either the embodied energy or LCA camp, or offer a stripped down version of these methodologies (the Forest Stewardship Council at www.fsc.org , for example).
Embodied energy is simply the amount of energy that has been consumed in the manufacture, transportation to site and, sometimes, use and disposal of a material. It may be quoted as 'cradle to gate' or 'cradle to grave'. Data about embodied energy can be given as a per mass figure or in terms of structural elements, as in the case of the BRE's Green Guide. Data for structural elements, can be more informative as it takes into account different structural and other properties.
The embodied energy of a building is generally low in comparison to its energy consumption over its life time. So why consider it at all? This is best understood by considering the parallel situation, where designers are paying increased attention to the airtightness of buildings. As the insulation value of building fabric increases, so the proportion of energy lost from the building through ventilation losses increases. Likewise, as the energy used during operation of a building decreases, so the embodied energy becomes a greater proportion of the total energy used by the building over its life.
It may therefore be worthwhile to use some high-embodied-energy materials in a long-life building if they deliver significant savings in running energy and to use low-embodied-energy, short-lived, easily recyclable or reusable materials and components in buildings with short design lives.
It is a fair assumption that materials with a high embodied energy are likely to be manufactured by a process that has negative environmental consequences other than purely energy use, for example in the case of ore-smelting which may result in heavy metal pollution. However, this doesn't always hold true (blowing foam insulation using gases containing ozone depleting substances (ODS) – thankfully a practice on its way to extinction – is a good example). Life cycle analysis can be used to quantify these other environmental impacts.
Life cycle analysis
A life cycle analysis (LCA) for a construction material rates its impacts from extraction or growth of materials through to its disposal. The methodology for an LCA could be extremely simple, a matter of ensuring consistent units throughout, for example. More rigorous methodologies would also ensure consistent data collection and, if more than one data set is being used, apply weightings to different data sets.
The international standards for LCAs are the ISO14040 series though results from different ISO compliant LCAs may not be comparable. As the BRE points out, there is “no single 'right' answer for applying LCA”.
If a building's performance is to be ranked against benchmarks then obviously a building-type-specific assessment needs to be used. Finding a suitable assessment method can be problematic for less common building types, or for buildings that are for mixed use, although the BRE can undertake bespoke BREEAM assessments.