Measuring environmental impacts
Those of us who design buildings are familiar with the degree of exactitude used to measure the performance and properties of materials. Buildings should not fall down, occupants should be guarded from fire and noise, expensive energy should not be wasted and the building envelope should protect from wind, rain and, increasingly in the UK, sun. Each of these functions is measurable and standards of performance based on measurement mark the success or failure of a function. Results are typically binary - pass or fail, yes or no, black or white. The only grey areas are on the colour charts of the paint specification.
And then … along comes the 'Environment'. In a way, we've all been used to at least one of its concerns for decades - the conservation of energy has been a focus of the Building Regs since the oil crisis of the 1970s. But this is a whole new ball game: we're not concerned anymore with just one resource but hundreds. And there's more, much more - how does the manufacture, use and disposal of every material and product we specify have an impact on the land we live on, the air we breath, the water we drink, the crops we cultivate and above all, the future we bequeath our children? And then, if we have that knowledge, what do we do with it?
The limits to measurement
There are two essential characteristics associated with the measurement and assessment of the environmental impacts produced by products and materials.
1 - The data is incomplete
The scale and complexity of ecosystems makes long chains of 'cause and effect' difficult to identify, even less to measure. However, it is commonly accepted that the more immediately calculable impacts associated with the manufacture, use and disposal of a product are the most important and provide a sound enough base for assessment and comparison.
2 - Some values are considered more important than others
Because much environmental data is incomplete, the complexity of impacts is hard to model and difficult to understand. Much of the unmeasured 'grey' areas continue to be the subject of debate.
Uncertainty is evident when we are called to draw-up a risks matrix - a crude (necessarily) form of risk management.
The scale of risk is a feature of 'ecolabel' schemes which seek to estimate the importance of each environmental impact in relation to others included in an assessment. In drawing-up such an order of importance of risk, 'weighting' is used to modify the data (see below)
There is a consensus that says that global warming is chief amongst the risks, but the relative importance of other impacts are contentious.
The pragmatics of construction can lead to conflict with other more familiar non-environmental values. An increasingly common encounter is through the design of insulation for the retrofit of solid-walled homes. The most acceptable solution is not always the best environmental outcome:
Example: Retrofitting internal v external insulation
The most efficient technique is to apply insulation to the outside face of an external wall. In this instance, with no planning constraints, environmentally conscious designers might look to resource efficiency as a very important value. Consequently they might specify wood fibre insulation from renewable sources for external application. However, if there are planning constraints, such as a listed building or location in a conservation area, external retrofitting is problematic. In this instance, the only possible intervention is to apply insulation to the inner face of the wall. Those familiar wtih refurbishment are aware that floor areas are usually at a premium and not all people welcome the thickness of woodfibre insulation eating into their rooms. In the struggle to provide identical overall u-value, the specifier will look to a more 'dimensionally-efficient' product - usually a non-renewable oil-based material such as polyurethane or phenolic foam. In this way, the value of preserving space for occupants effectively 'trumps' the value of resource efficiency and the pollution associated with petro chemicals.
Tools of the trade: the Life Cycle Assessment (LCA)
Though the science of environmental impact analysis is still developing, a common methodology has already evolved and is in widespread use throughout the world. Apart from its being conceptually straight-forward, it also benefits from early standardisation by the International Organisation for Standardisation (ISO) in the form of ISO 14040.
An LCA looks at the processes involved in the manufacture, use and disposal of any given product (LCAs are used to assess all products, not just construction products). An LCA procedure will typically measure things such as the use of raw materials, water and energy as well as bi-products such as factory emissions, waste and the effects of different forms of disposal.
LCAs are broadly concerned with:
• Climate change
• Ecosystem quality
• Human health
Example: Below are the measured environmental impacts of 1 m2 of a wood sheet cladding product made in Norway:
Global warming potential (kg CO2 equivalent): 0.44 kg
Ozone layer depletion potential (kg R11 equivalent): 1.1 kg
Acidification potential (kg SO2 equivalent): 0.005 kg
Eutrophication potential (kg PO4 equivalent): 0.001 kg
Photochemical ozone creation potential (kg C2H4 equivalent): 0.0004 kg
The essential nature of LCAs is that they are designed to be comparable. Notice that the impacts are expressed in terms of 'equivalent'. An equivalent figure is used in order to harmonise LCA figures. For example, not all global warming gasses produced by industrial processes are Carbon Dioxide - others include methane and nitrous oxide. To make life simple, although different gases might be produced in the manufacture of different products, it is useful for purposes of comparison to expresses all greenhouse gases as just one gas. So if a process produces only methane as a gas, the LCA will express it as a Carbon Dioxide equivalent.
• More information about LCAs….
Tools of the trade: the Environmental Product Declaration (EPD) (aka Type III label)
In terms of information provision, EPDs are super-charged LCAs. Like LCAs, EPDs have been standardised by ISO, in this case ISO 14025. EPDs have been designed as definitive information documentation published by the manufacturer of the product.
At the core of each EPD is the LCA of the product, but other useful information is included such as a break-down of the materials used as well as an account of the manufacturing process.
EPDs are becoming the foundation stone of environmental impact assessment.
• More information about EPDs….
Tweaking the numbers to make sense: Weighting
'Weighting' is a feature of some common 'eco' label schemes.
(• more information about eco labels)
Weighting is a device by which the degree of importance can be assigned to each environmental impact category. Weighting is used by some 'green' rating schemes as a component in the way of providing end users with a simple rating eg A, B or C.
The measured impacts from each issue are typically multiplied by a % figure that represents the importance attached to the issue by the assessors. The higher the %, the more important the issue is considered to be.
If for example we took again the impact measurements for the Norwegian cladding, typical % weighting figures might look like this:
Global warming potential: 0.44 x 36%
Ozone layer depletion potential :1.1 x 7.7%
Acidification potential: 0.005 x 4.8%
Eutrophication potential: 0.001 x 4.1%
Photochemical ozone creation potential: 0.0004 x 7.7%
The results are designed to provide guidance to understanding the relative importance of any given range of impact data.
• It's important to note that whereas impact data is measured, weighting values are opinion-based. Standards based on such formulae inevitably reflect the concerns of those who devise the weighting adjustments.