Assessing embodied impacts using BIM
Building information modelling opens up opportunities to assess the embodied environmental impact of a building and really understand its eco-footprint, writes Daniel Doran of BRE
Report from – Daniel Doran
Building information modelling (BIM) opens up fantastic new opportunities for construction professionals to understand the environmental impact of the buildings they work on. Most will be aware that BIM energy modelling is an effective way to assess operational carbon emissions, but in terms of a building’s environmental footprint, this is only half the story.
Powerful new BIM tools are now available to assess the embodied environmental impact of the building itself. A building’s embodied impact is the sum of the impact caused by all the construction material production plus the transport, installation, maintenance and repair, and end-of-life disposal. Embodied carbon is the best known embodied impact indicator, but other examples include water, resource use and toxicity.
Embodied vs operational carbon
The relationship between operational carbon and embodied carbon is an integrated design consideration. For example, triple glazing has improved insulation and should reduce operational carbon, but the extra layer of glass means more embodied carbon.The question is: how many years of operational savings are needed for the extra embodied carbon to start having a net benefit?
As an illustration, if a building’s overall operational carbon emissions are 50kgCO2/sq m/yr and embodied carbon is 1,000kgCO2/sq m it would take a couple of decades before the operational savings catch up with the building’s embodied carbon. If grid decarbonisation happens in the UK (so energy generation emits less carbon, as is required to achieve statutory UK targets) this time period will increase substantially.
What’s more, embodied carbon from the production of construction materials is all upfront, contributing to global warming even before the building is opened. So, with only a short time – if any – to avoid dangerous climate change, it is clear that embodied carbon should be taken very seriously.
Reducing embodied impacts
The embodied impact of different construction materials varies enormously and consequently decisions made on a small scale can add up to a substantial difference at the building level. If material A has half the embodied carbon of material B then, all other things being equal, A would represent a significant saving overall. Unfortunately, it is rarely that simple.
Material B may be inherently stronger than A, so less is required to achieve the same function. Or A might be a sheet material that requires an additional substrate C for structural integrity. Alternatively, A might have a long service life, while B needs to be completely replaced half way through the life of the building. When all materials in a building, the relationships between them, varying quantities, different service lives, etc, are taken into account, assessing embodied impacts can be a complex and time-consuming task.
To simplify and make the process of manual embodied impact assessment manageable for construction professionals, the Green Guide to Specification has been widely used for many years, in BREEAM and the Code for Sustainable Homes, for example. It is a quick-reference element-level assessment method and, as with all simplified solutions to complex tasks, does have some drawbacks. However, for many design teams, it remains a manageable approach to manual embodied impact assessment.
With the wider use of BIM it is now viable to produce software tools that offer automated building-level assessment. With this automation comes the processing power for greater functionality, better accuracy, integration, a detailed breakdown of results and compliance with new European standards, in particular, BS EN 15978.
BIM’s capacity to include material information, to measure quantities from drawn geometry and number crunch the results – the essential ingredients to embodied impact assessment – means that what would have taken days manually can now been done in seconds. As the uptake of BIM has grown over the past five years a number of new embodied assessment tools have emerged. However, the level of BIM integration is variable, which has implications for workflow.
Standalone embodied assessment tools require scheduled quantity data or a model to be imported from a separate BIM modelling application each time an assessment is carried out, resulting in an inefficient workflow. This can be overcome by opting for embodied assessment tools that are incorporated within (or are a plug-in to) widely used BIM applications. However, the holy grail of BIM is for information – and therefore collaboration – to flow freely between different organisations that use different applications and platforms. At the forefront of this is the openBIM IFC initiative. The scope of IFC is ever increasing and work is soon to be completed on including comprehensive embodied impact information.
Building-level assessment – the benefits
Beyond speed and workflow integration, the ability to carry out automated building-level embodied impact assessment has further major advantages. Building-level assessment means results are building specific. Rather than selecting from a library of pre-assessed element constructions (generic wall type A versus generic wall type B) the user is able to enter building specific detail for each material, including thickness, density, service life, site waste and transport distance.
For example, service life can vary considerably depending on installation, weathering, wear, imposed stress and, not least, early replacement due to churn or commercial branding changes. All these criteria are specific to a given building design and are best known by the design team. As service life directly affects the number of replacements over the life of the building (a carpet with a 10 year service life will be replaced five times over a 60 year life), these details can make a substantial difference to the building’s overall impact.
Building-level assessment allows building-specific high-impact elements like substructure to be included, which cannot be adequately assessed generically. This is because the design of a sub-structure system largely depends on the specific ground conditions and overall building design.
Integration with assessment schemes
The benefits of building-level embodied impact assessment are recognised by building environmental assessment schemes like BREEAM. BREEAM New Construction now rewards the use of robust building-level embodied assessment tools through two new exemplary level credits. These credits are awarded for using these tools (to certain quality criteria) rather than being linked to quantified performance.
A prerequisite to assess quantified performance is that benchmarks are developed first – so there is something to measure performance against. It is widely accepted that insufficient building-level data exist to produce robust benchmarks now. Therefore, BRE will gather data from BREEAM schemes applying for the exemplary credits. Once a sufficient sample of real project data exists, BRE intends to produce and publish benchmarks for different building use types. BIM based building-level assessment can then be phased in as a means for assessing the main materials credits in BREEAM.
So the industry is increasingly aware of embodied impacts (particularly carbon) and BIM has enabled powerful new tools to emerge that can integrate embodied assessment into existing workflows. The building-level assessment standard BS EN 15978 has been published and assessment schemes like BREEAM are now rewarding building-level assessment. As such, forward thinking consultancies are increasingly offering these services. The stage is set for building level embodied impact assessment soon to become a mainstream activity.
Daniel Doran is senior consultant at BRE leading the IMPACT project. IMPACT is a specification and dataset for the incorporation of building-level embodied impact assessment and life cycle costing into BIM applications. More information is available at www.IMPACTwba.com or in the new IHS BRE Press publication, Advances in construction life cycle assessment through building information modelling, which is available from BRE Bookshop. An edited version of this article was first published in the Construction News 2013 BIM supplement.