Are you visiting from outside your region? Visit your regional site for more relevant services and pricing.

Rating environmental assessmentsMay 2012

Finland hosted the eleventh World Sustainable Buildings Conference. Roderic Bunn headed to Helsinki to pick up the latest thinking on climate friendly construction practice.

Grandly titled, the four-day World Sustainable Building Conference in Helsinki certainly packed them in: 1020 speakers and decision-makers from 52 countries, 310 oral presentations in 15 minute bursts, and no less than seven - yes seven - parallel seminars. All that, and 200 posters on continuous rotation.

Blink, and you missed something. Stop for a coffee, and you lost an entire session. At any one moment there were more delegates running between seminar rooms than were sitting. The pursuit of sustainability had never been so stressful.

A large number of presentations reflected on the value, or otherwise, of the various environmental assessment schemes mushrooming around the world, such as LEED from the US, CASBEE in Japan, Greenstar in Australia and of course BREEAM in the UK. Marketing of these schemes was mercifully confined to plenary sessions, leaving the international researchers to make the more insightful assessments. Many of their observations would strike a chord in the UK, which is why it's worth looking at them in depth.

Rating the ratings

Dr Umberto Berardi of Politecnico di Bari, Italy, compared the LEED, BREEAM, CASBEE, GBTool, Green Globe, and the Italian SBC-ITACA rating systems to find out how they are really being used.

Figure 1: The percentages of the weights assigned by six sustainable rating systems for seven catgories of sustainability. Source: Umberto Beradi.

These sustainability assessments are multi-criteria systems, and rely on site, water use, transport energy, and energy use data. Berardi found that the weightings given to each criterion are generally not explicit, so he set out to identify what aspects tend to be given more consideration by users.

The way each system categorises things caused Berardi some difficulties. He found that system structures were not always easily accessible, and criteria among different systems did not perfectly overlap. Berardi and his team were forced to create an 'others' category for criteria that did not fit into
the other six categories (such as management and innovation aspects).

So, for example, while LEED assigns seven per cent of its credits to innovations, BREEAM has 15 per cent for construction and construction waste management, Green Globe has 12.5 per cent of its points in 'others' including project management, while the 'others' in CASBEE includes points for mitigation and off site solar energy gain. GBTool has the largest percentage of points in 'others', as this rating system includes a cultural perception of sustainability. Instant confusion.

The results from Berardi's comparisons are shown in Figure 1. Energy efficiency is demonstrably the most important category (the weight average among the six rating systems being 25.5 per cent), followed by indoor environmental quality, waste and pollution, sustainable sites and material and resources. What's striking about the data is that environmental aspects receive more attention than economic and social ones.

Figure 2: The distribution of LEED credits chosen by building designers, from a sample of 490 LEED-assessed buildings. Source: Umberto Beradi.

The issues identified by Berardi are not new. Such differences between the rating systems partly led to the foundation of the Sustainable Building Alliance, the role of which is to establish common evaluation categories and to improve system comparability. The issue is whether the aims and objectives of the rating tools are being applied in the way intended by their designers.

Berardi therefore looked at how the market has been applying LEED, using a sample of 490 LEED-assessed buildings (Figure 2). Berardi found that while the design of the rating tool might be scientific, the choice of criteria to gain credits was rather less so. There was also a lack of a life-cycle perspective. Up to the Platinum level, the data reveals that energy and atmosphere credits were less attractive to building clients and their design teams.

Is this because getting the energy credits is more onerous and costly than other credits? Or is it that some credits - sustainable materials for example - are easier to get simply because the construction industry is now routinely producing more sustainable products?

Pushing the boundaries?

Dr Chris Pyke, research director for the US Green Buildings Council (US-GBC) provided useful insights by analysing the trends in the use of the LEED rating system. Pyke's research team gathered data from over 3300 LEED-assessed buildings from 2006, including buildings from outside the US.

Since 2000, LEED has certified 8189 projects in 130 countries. Of those projects, 3335 were certified under the New Construction Rating System, and 184 of these achieved the highest certification level (Platinum). Of those Platinum buildings, 47 were based on LEED New Construction Version 2.1 (released in 2002) of 699 buildings, and 137 to Version 2.2 launched in 2005.

Figure 3: The percentage breakdown of LEED certificates 2006-2011. LEED Platinum is still rare, with the favoured levels of certification being consistently the silver and gold categories. Source: Chris Pyke US-GBC.

As Figure 3 shows, the percentages of clients achieving Platinum status has remained fairly static, despite a large increase in the uptake of LEED in the last three years. Only in 2007 did Platinum buildings rise about 10 per cent of the total. As Chris Pyke observed, "Platinum is a rarified layer".

The other important issue with this data is that the buildings aiming for Platinum are very different to other buildings, almost to the extent that they are not comparable with buildings with other LEED ratings. "Platinum buildings tend to be for not-for-profit organisations or government," said Pyke.
"A disproportionate number are owned by essentially mission-driven organisations." The buildings themselves also tend to be small - 75 per cent of them are smaller than 7000 m2.

Pyke reported that some credits are more routine: site, transportation, water, heat-island affect, and energy and atmosphere credits. Building-integrated renewables are rare across the dataset, and only tend to be a feature of Platinum buildings. Under LEED Version 2.2, 80 per cent of Platinum projects
achieved the credit for renewable energy while only 14 per cent of all projects achieved the credit. "People who are striving to get that designation are more willing to invest in renewable technologies," said Pyke.

Pyke also observed something more subtle: LEED clients don't tend to look at the envelope if they are aiming for Platinum. "Based on the rankings in the rating system, the incentives to invest in materials are not strong enough," he said. "Similarly, there are no incentives in Platinum to make you want to locate on a brownfield site."

This raises a question of the rating systems' ability to motivate improvements in passive design rather than active systems, with all the latter's inherent high cost, technical risks and operational complexities.

In common with similar rating systems around the world, the US-GBC is grappling with increasing focus on operational performance. Moves toward including monitoring and verification in LEED 2012 are adopting multiple lines of attack, such as Energy Star Benchmarking and Minimum Program Requirements (MPR6), which will require five years of performance data on all projects. (LEED 2012 is scheduled for release on 7 November 2012.)

The US-GBC is also introducing a voluntary programme called the Building Performance Partnership, a system of data collection and analysis that provides a platform for performance feedback from all LEED certified projects. This includes both residential and commercial buildings. Participants will benefit by receiving annual performance reports, report cards, and "real-time data interfaces to aid in meeting building performance goals". The intention is to "optimise building performance by creating a green building performance database, developing standardisation of reporting, and establishing new performance benchmarks," said Pyke.

Figure 4: The Green Building Information Gateway (CBIG), a beta version of an on-line database of all LEEDassessed buildings. To see this example go to

The US-GBC is already trialling a beta version of its on-line database, the Green Building Information Gateway (Figure 4), similar to the UK's Carbon Buzz website.

Anna Posten, a PhD researcher from Glasgow Caledonian University added her voice to the continued criticism of environmental rating systems and their one-size-fits-all approach to assessing buildings. Posten has reviewed the main international tools, and like others working in the field found that the calculations behind the rating are not transparent. "If we don't understand the tools properly" she reflected, "we won't understand what we are trying to achieve."

"If these tools …remain limited in scope, the sustainability understanding of an entire generation of practitioners will be based upon precepts that do not hold true in achieving sustainability, " said Posten. "As we move towards a more holistic, qualitative, whole-life method of assessment, other tools and methods will be needed to connect buildings to the wider issues of location and culture."

The international dimension

Which was precisely what the BRE's Martin Townsend was on hand to promote - the broader scale of sustainability and how BRE Global intends to develop BREAM to be the international assessment tool of choice.

“The connection between the building, the review process and the community is an exciting space we need to be in” - MARTIN TOWNSEND, BRE

Townsend's vision places BREEAM at the centre of a data repository for all key stages of a building project. He saw a time when spatial planning, statutory planning and applications, post construction reviews and post occupancy evaluation all feed into an online central BREEAM database.

In advancing this ambition, Townsend argued that "We are only going to be successful in actually making better spaces for people and communities…if we understand what we got right. Communities need to engage with local authorities and developers, forming relationships with organisations to create policies that will drive change."

"If we are serious about sustainability, it's about making sure we learn," added Townsend. "It's important that we know what works and what isn't sustainable."

This, of course, is an ambition shared internationally, not just by BRE Global. LEED, via the US-GBC, has similar ambitions for cross-scale assessments.

"Our goal" said Chris Pyke, "is market transformation. We want to change the conditions of the built environment, creating communities and buildings that are better for people and the environment."

The US-GBC has spent eight years incubating a set of new tools and approaches to achieve this object, and is now into "full active participation and public comment" on three interlocking LEED tools: LEED for New Construction, LEED for New Development, and LEED for Interiors.

"In LEED 2012, we have identified a different set of outcomes (to these tools) while applying same constructs. We are applying it to a fancy database that allows it to associate strategies with outcomes across multiple criteria: such as control, magnitude, and duration. Fundamentally, it's a matrix of things you can do, things you want to abate, the associations, and a way of knowing how successful a strategy will be.

As the indexes are calculated, at each scale - one for new construction, one for neighbourhood, and one for commercial interiors - the results they generate will be complementary," explained Pyke. "At neighbourhood scale I'm talking about transport, infrastructure and land programming, at the single building level about design operation and the transport and construction of the building, while at the commercial space level it's about building services systems and purchasing."

It seems LEED 2012 will deliver pretty much what BREEAM is aspiring to do: a very close-coupled rating system that can create an equivalent index for a neighbourhood, new construction and interiors of a building, all of which can be used to inform decision-making at various scales.

The grand ambitions of the assessment providers require the mechanics of the assessment process - and the metrics that underpin the credits and the weightings - to be scientifically and statistically accurate, robust and repeatable across different contexts.

Which brings us neatly to the accuracy of measurement of environmental factors and the accuracy of the tools and computer models. And to Reading University's Howard Darby, who has been studying the standards and software tools for assessing operational and embodied greenhouse gas emissions.

Darby found a lack of a standardised approach to the calculation of embodied energy and of reliable data on emission factors for building materials and processes. "There is a lack of a consistent and accepted approach to the calculation of embodied energy" said Darby, "and the relationship and interaction between it and operational energy is not well understood. There is also considerable uncertainty and variability in the available information on emission factors for building materials and processes."

Darby based his analysis on a book storage building in Swindon. Completed in 2010, the building is a 11 578 m2 steel-framed structure on mass-concrete foundations, housing a mix of offices and stores. Darby studied the building's fixed structural and services elements, (ignoring the furniture and fittings) and ran the properties through the simulation packages CES Eco-selector, EA Carbon Calculator (a free on-line package), and Envest 2 from the BRE. Darby analysed each program for its suitability for all phases of the building's life, the transparency of benchmark data, and the programs' ability to provide a good breakdown of results.

Darby relied on the generic embodied-energy sources promoted by the steel and timber associations. He also based his assessments on a typical building life-cycle, assumed natural sources of construction raw material, and factored in conventional means of transport. He then ran the building through a conventional life cycle, from construction through to occupation, maintenance, demolition and re-use.

Figure 5: The embodied energy estimates of simulation programs. The percentages relate to the difference between maximum and minimum values.

Figure 5 shows how each program performed in terms of carbon dioxide emissions during a modelled build phase. The embodied energy figures differed significantly between the programs, but also varied by up to -30 per cent and operational energy by +71 per cent compared with Darby's manual calculations. For example, cradle-to-site estimates differed by 34 per cent (1477 tonnes of CO2), while cradle-to-cradle (Eco-Selector estimate only) differed by 43 per cent (1655 tonnes of CO2).

"I know that carbon assessment is not a very precise science," concluded Darby with some understatement, "but 43 per cent is probably a bit more than you would expect to get. There was also a wide variation in the emission factors for materials and a lack of transparency in the calculations."

So, yet again, the warning about the software tools that unpin environmental impact assessment once again applies: use software tools with care. "Different assumptions and boundary conditions can produce widely differing results" said Darby, "and confirms the need for standardisation of EC data and assessment methods."

Darby's study was also useful for understanding the relationship between embodied energy and operational energy, as Figure 6 demonstrates. Figure 6 shows a simplified straight line curve for operational carbon dioxide emissions over the building's anticipated 60-year life, plotted against the embodied energy (with three m&e refits at 15, 30 and 45 years, and a general building refurbishment at 30 years). Without decarbonisation of the power supply and similar site-based improvements through component re-use and renewables, the crossover is at 25 years.

Darby then applied two weightings. One was based on the assumptions in Publically Available Standard PAS 2050 (a method for assessing the life cycle greenhouse gas emissions of goods and services). Darby also applied a weighting for the carbon dioxide emission reductions based on the government's Markal-Med model scenarios for decarbonisation of the electricity supply by 4000 tCO2 between 2010 and 2050.

Although PAS 2050 only had a modest effect on embodied energy (possibly due to the relatively short building life), the use of a value for the the intended decarbonisation of the electricity supply had a large effect on the operational energy.

"If this is going to be the case," said Darby, "are we right to be making more of the operational carbon reductions, when we should making more of embodied energy reductions?"

Darby's work adds yet more weight to the growing evidence that embodied energy becomes more significant as operational energy is decarbonised. Which means that the buildings we build today need to be as future-proof as we can make them.

BSRIA provides a range of building compliance services including BREEAM. For more information contact us on:

T: 01344 465600


A unique resource of technical and market knowledge