Let's talk "coverage" or "completeness" of WLCAs

I would like to discuss the “coverage” of LCAs (or lack thereof) and the implications on reporting.

“Coverage” or “completeness” refers to how much of the actual building material is being captured in WLCAs at any given stage. This is particularly pertinent where there is policy (being) established to assess WLCA; and/or where someone is scrutinising that assessment and comparing to benchmarks; and/or where hard limits are being set, or have been set, for embodied carbon impacts.

State of Practice (Industry)

At the earliest design stages, you can imagine (or you probably experience) that designers are most reluctant to provide material quantities. Of course, for some building components, this is less of a hurdle (e.g. structures); but for other components, this is more challenging (e.g. the envelope, internal partitions and doors, internal finishes). And then MEP (before construction) is not only too conceptual to get quantities, but the EPDs and carbon data is sparce (granted, it is improving). Sure, some benchmark data points exist, compiled by various organisations / carbon data providers – but they’re not brilliant: they’re not sufficiently transparent for us to understand what level of coverage they give (and in fact, our experience is that they are underestimating the impact of the material that’s actually being installed when it comes to construction).

I’m afraid that experience shows that improving carbon assessment coverage/completeness can be challenging. Traditional industry scopes don’t make it clear who is quantifying much of the material; not all the data needed for an LCA needed to be quantified for other reasons like cost. And at early stages, there’s insufficient time and interest to pay for that quantification (or even working out rough allowances) to happen. Designers don’t want to be the one to provide quantities because of perceived liabilities too.

Using Cost Plans

In UK practice, there is a requirement to align with, and achieve 95% coverage of, the project cost plan. However, again, cost plans doesn’t necessarily suit the carbon assessment exercise. Many costs are estimated through benchmarks and historic data; most things don’t need to be quantified.

I’ve also seen independent assessments that explicitly say that 100% of a building component category has been assessed at Concept design stage (presumably to satisfy the “95% coverage” requirement required by local policy), but only a few placeholder materials have been input with benchmark data, aligning with the concept stage-level of detail in the cost plan. It is plainly clear (from our experience…) that significantly more material is going to be identified in detailed and technical design stages, but the early assessment (and statement of 100% coverage) gives many people (clients, designers, other consultants, local authorities) a sense that the impact is going to be really low compared with regional benchmarks, without those clients & designers having to do anything particularly different.

In other words, I’m not sure there’s enough discussion about the reality that early WLCAs probably haven’t / aren’t actually capturing a lot of important material, and building carbon footprints should really be higher.

Looking forward

As LCA practice improves and more data becomes available, we see carbon assessment results are trending higher because more is being properly accounted for. This will be true for those who are most rigorous and thorough in assessment; not necessarily true for those aiming to capture the big elements they recognise, and who gloss over the many smaller pieces, or don’t realise what they’re missing.

Clients and designers loathe a carbon assessor surprising them with a higher impact than they expected, e.g. because their previous project assessed lower. It’s a thankless job, being a thorough assessor, capturing as much material as possible; and I suspect there are plenty of people happy to do a quick assessment reflecting concept-stage Level of Detail and spit out a small number, for less fee.

“Completeness”/“Coverage” is not a popular enough topic / high enough on the agenda to have a conversation with clients and designers yet; hence this thread.

Concluding my conversation starter

I could carry this on for a while – for example, I could talk about the different targets being set by different regions, and how low targets raise the question of the thoroughness of the data informing them; or how achieving those targets will be more challenging if “completeness” improves… But let’s not talk about the wider implications for now…

Thoughts? What are others finding?


First, let me say that this is a huge topic that is difficult to respond to completely. What follows is my attempt at an answer that is based on our efforts to understand what targets we should be setting for embodied carbon reductions.

Yes this is an important topic that I think most in our line of work have come across. I have looked at baseline (or benchmark) studies from CLF (2017), deQo (2017), Carbon Heros One Click LCA (current), and various studies including “Towards embodied carbon benchmarks in Europe” by Ramboll (2022), AIA COTE, MDPI Sustainability Journal (2018), “Embodied Carbon Benchmarks for European Buildngs” by One Click LCA (2021), benchmarks set by RIBA, LETI and WBCSD, and many case studies too numerous to mention.

What we have learned is that the life cycle stages considered, the scope and completeness of building systems included, and the timing and accuracy of the BIM that populates the amounts of materials considered are the biggest factors for the wide range of baseline values out there today.

The consistent reporting of life cycle stages, and the scope and completeness of building systems included are starting to be addressed with WBLCA reporting templates and guidelines such as those by CLF, RICS, LETI, and WBCSD. The timing and accuracy of the BIM work by the wide range of those who perform WBLCAs is harder to control.

For setting targets within our collaborative for use until better databases are developed by national and international organizations, my opinion is that baselines are best based on LCAs for each building system as determined by the disciplines responsible for each system. Realizing that this is an ideal that is difficult to attain, our current focus is the development of ranges of embodied carbon for each building system as a way to validate the embodied carbon values provided for each system, or to supplement those values that are not provided. These ranges can also be used to estimate the WBLCA early in design.

Life cycle stages are key to this conversation as well, and my understanding of most baselines is that they generally include stages A1-A5 and that some extend through stage D. The embodied carbon for stages A1-A5, for a short time frame such as now to 2030, is the highest value embodied carbon regarding staying below a 1.5 C target. Ideally all life cycle stages would be included in a baseline studies as this would include benefits such as the recycling of steel, the reuse of building components, and the sequestration of carbon in wood products.

In using the building system approach to determine ranges of embodied carbon, there are several examples of progress including the CLF studies for interiors (including FF&E) and MEP, and the SE 2050 Challenge which is collecting data from over 100 structural engineering firms for the structural system embodied carbon amounts. Using these studies and the other resources mentioned above, our organization, the Colorado Embodied Carbon Collaborative, has started developing ranges for each building system to use until more thorough baselines are developed.

We are anticipating that CLF will release an updated baseline study later this year, and we have the expectation that it will be a good resource. We are also watching England for the work being performed by the Built Environmental Carbon Database. A third benchmarking effort in the works is by Athena in Canada. There are more out there, I am sure.