The challenges of doing embodied carbon calculations
Last week marked the end of a 9-month long ‘NetZeroFlow’ project part funded by Innovate UK’s Sustainable Innovation Fund, in which xbim and Circular Ecology joined forces to develop a solution enabling architects and engineers to measure and reduce embodied carbon as their designs evolve.
Driving carbon down to ‘net zero’, and improving life cycle assessment, are being addressed by many, but this project has had the combined 60 years’ experience of the xbim co-founders behind it. xbim’s expertise in liberating and improving BIM data means that they are uniquely placed to challenge the existing status quo; carbon life-cycle assessments are hard, often done late (RIBA Plan of Work stage 4+ with no check after that point), and far too late to impact on consequential decisions made to drive carbon down at stages 0-2. BIM can help and, more importantly, xbim can help.
The way that current carbon costing calculation and analysis is carried out has some challenges:
- It’s expensive to carry out and making changes as a result of embodied carbon and lifecycle assessments adds to that expense.
- It’s document centric (drawings, schedules, specifications), with documents often inconsistent, incorrect and quickly out of date.
- It’s time-consuming to do (therefore adding to the expense).
- It’s error prone, subjective and often manual because it’s human driven.
We also quickly became aware that there are no reliable benchmark standards for lifecycle assessments (LCA) for carbon, so the LCA design targets typically fail to be met by the final project results (e.g., on buildings, railways etc.) and don’t drive down carbon to expected levels, such that ‘carbon offsetting’ becomes the only mitigation.
Can BIM help solve the problems with calculating embodied carbon in a design?
Yes, but it’s not a panacea. While BIM models contain most of the information required to undertake a carbon assessment, using BIM introduces challenges too; BIM data can be complex and messy, so the information in models needs to be checked before it’s used for LCA (a process which is also needed for carrying out scheduling, costing, construction, installation and ultimately, asset management). Without robust quality assurance processes, the potential for errors and omissions can have major implications for carbon assessment, safety, cost and constructability.
We identified a number of issues impacting undertaking LCAs from BIM data:
1. The prevalence of proprietary BIM software:
- Deters collaborative working, reducing the understanding of ‘big picture’ LCA impact
- Results in fragmented solutions since each design tool requires its own LCA solution
Xbim believes that measuring carbon in open standards such as IFC has significant benefits when looking at the whole building performance, since carbon is not only an Architectural consideration, but can be significantly impacted by the designs in specialist engineering models (e.g. Structural and Mechanical models). E.g. A Revit add-in can only give a partial view of the embodied carbon in your design, not helpful if the steelwork is modelled in another authoring tool.
2. Lack of relevant quality assurance processes for BIM data lead to:
- Naming and Classification inconsistencies
- Errors introduced in Data Exchange and Extraction
- Too much data supplied – information overload
- Missing data – meaning you don’t have the full picture to accurately measure
Without rectifying this, any material quantification from BIM sources can lead to “RIBO” (“Rubbish In, Rubbish Out”). While QA tools (such as Autodesk Navisworks and Nemetschek Solibri) exist to quality assure BIM models, the reality is that the process is costly and time-consuming to perform, and a significant degree of manual effort is needed to conduct a QA review. A more automated approach is needed if the LCA process is to be streamlined.
3. Taxonomy mis-matches between carbon libraries and ‘elemental breakdowns’ in BIM models:
- Carbon library datasets typically define CO2e impacts of fundamental materials (concrete, steel, plastic etc) over various lifecycles (“Cradle to Gate” etc) based on a variety of units (e.g. weight, length, volume of material)
- Building elements in BIM models often provide quantities using different units and measurement semantics, with actual materials defined at a different level. This leads to complexities in extracting material quantities. e g.:
- Given a wall with a known area/volume what is the composition (and material) of block, insulation, air-gap, stud and plasterboard in kg, m2, m3 ?
- Given a window of some dimensions, what is the composition of wood, aluminium, plastic, glass, steel etc comprising that product, and what are the material weights/volumes?
- Consequently, it can be complex to accurately quantify materials in an entire model.
Mapping materials in a BIM to a carbon library material is imperfect and may result in a range of possible values. Without solving this challenge quantification of the design from a model requires significant human intervention to calculate quantities and associate materials. Any automated LCA service needs to be able to extract accurate material quantities from a design. As specialists in BIM standards, the xbim team were ideally situated to address this issue.
4. Versioning and change control challenges occur as a result of:
- Poor adherence to exchange protocols
- Multiple organisational boundaries
Carbon assessments need to be conducted iteratively through the project if the design team is to truly demonstrate that carbon impact has been optimised throughout the development. This raises challenges identifying and validating what has changed between designs, and the impact on the LCA. “What was the CO2e impact of the last design revision, and where was the improvement?”, and “Was there a design change…, or are we simply missing half the models?”
How we address these issues
Xbim’s mission is to tackle poor quality data in BIM data exchanges using scalable, open standards and an automation engine which drives out errors in large building models, creating better quality data.
By using this enhanced data, and a completely automated process, we can deliver reliable BIM data that allows consistent carbon calculations across large portfolios of buildings in minutes, not months.
The project set out to overcome the main challenges, as detailed above, in four steps:
- By developing an OpenBIM workflow automation platform, enabling LCA and other sophisticated analysis and processes using BIM data to standardise, and be run outside of proprietary design tools.
- By building an automated BIM rules checking system using the workflow platform to conduct BIM Quality Assurance on models, ensuring they meet requirements.
- By establishing an approach for quantifying materials in a BIM from fundamental geometric representations. This enables accurate measurements of dimensions/quantities of materials in complex products in a model without relying on (often flawed) design tool measurements.
- By establishing tools for comparing models and LCA assessments from different versions of model inputs and reporting in a way that’s simple to understand.
In conjunction with Circular Ecology, the project has also extended and updated the “Inventory of Carbon and Energy” database (known as the ICE database) to cover new material classes and doubled the number of material ‘data points’ from current data source, as well as extending the data set to include common products as part of this project.
The xbim workflow engine solution
A fundamental goal of the NetZeroFlow project, has been to simplify the whole LCA process by automating how a carbon assessment from BIM data is conducted, eliminating the manual error prone steps. In order to automate the process of conducting an embodied carbon assessment our project developed a new workflow engine for OpenBIM, built on the xbim Flex cloud platform. Workflows are a sequence of customisable steps, that for example: allow design inputs to be put through a pre-defined set of checks, assessed against a set of rules, allowing BIM information to be normalised, classified and quantified, to achieve the most accurate material take off.
The xbim Workflow service is completely user definable and so also has the potential to automate other routine BIM tasks and offload them to the cloud – to be the QA for BIM if you like.
The Results
Just some of the successes of the NetZeroFlow project include:
- Simplifying the process of embodied and life cycle carbon assessment by joining up BIM & LCA, and ensuring model data can be automatically quality assured and processed for accurate LCA quantity take-off.
- Shortening the time taken to do an assessment to minutes, by digitising the necessary workflows.
- Automating the process so it can be done more than once per project, enabling benchmarking and historical comparisons.
- Reducing the pain and cost of assessment by cutting out the paper and pdf cross-referencing of drawings, specifications and schedules.
- Improving data quality and consistency in BIM outputs.
And perhaps most importantly, opening up the ability to automate other BIM processes to improve costing, asset management and collaboration.
Practically the xbim automated workflow system means you can take data from any design tool, in OpenBIM data formats, to calculate the carbon content of a design. Using the interactive LCA report you can then assess the impact of changing elements of the design. For example, on the face of it, it might look like changing the window specification will make a difference to CO2e, but the outputs of the LCA report can show you that greatest impact can be achieved through, say, a different wall construction. You can then amend the design based on informed decisions and reassess across multiple iterations, and subsequently use these to benchmark for carbon (by building type) and drive towards net zero carbon targets.
What this means for xbim is that our partners can validate, query and benchmark BIM data for their clients, whether they’re managing property portfolios, data centres or highways. It allows for informed and impactful decision-making in the fast-paced, fee driven design stages. More importantly xbim’s workflow engine will unlock further innovation potential in the construction sector by enabling other manual, routine tasks to be executed in minutes rather than weeks. Carbon assessment is only one of many potential use cases.
If you find you are constantly repeating yourself with BIM data and have suggestions for workflow engine use cases, we would love to talk to you – Get in touch.
You can read more about the background to this Innovate UK funded project here.
