Look at buildings as a whole for the most efficient carbon outcomes

Whole-life carbon or upfront carbon plus energy use? What should the new London Plan limits cover?

The Net Zero Carbon Building Standard (NZCBS) gives us the answer. The NZCBS provides limits for upfront carbon, and energy use, but states that it is the intention for the standard to evolve to provide whole-life carbon (WLC) limits when there is sufficient data available. The question is, have we already reached that point?

The existing GLA policy SI2 (which I co-authored in 2021-22) required full WLC reporting but did not provide limits for the same reasons as NZCBS, although policy SI2 does provide benchmarks for guidance. This was several years ago, and much more WLC data is now available. Let’s examine the issues.

To fully optimise both carbon reduction and resource efficiency we need to do two key things: Firstly, we need to consider the structure, the building envelope and the expected energy use together in an integrated, holistic way, and secondly, we need to examine the carbon impacts of all life cycle stages, ie upfront, in use and end of life also in an integrated and holistic way.

For example, design decisions for the structure and/or envelope have consequences for energy use, or material and product choices made for the upfront stage have impacts for the in-use and end of life stages. Buildings are complex organisms and therefore a siloed approach of looking at lifecycle stages or building elements and energy independently of each other does not produce the most carbon or resource efficient outcomes.

The NZCBS limits get increasingly onerous as we get closer to 2050. Achieving these will become much more difficult unless we adopt fully integrated thinking across both the design disciplines and the building life cycle.

The key problem with focusing on upfront carbon is that durability (ie maintenance) and disposal are no longer prime considerations. This can be incredibly wasteful in resources

The key problem with focusing on upfront carbon is that durability (ie maintenance) and disposal are no longer prime considerations. This can be incredibly wasteful in resources; both in materials due to replacements, and energy leakage as the envelope deteriorates over time. A lifecycle assessment covers 60 years which is just a blink of the eye in climatic terms.

WLC assessments done today only take us up to 2086, not even to the end of the century. Therefore, the emissions over this period should really be considered as a single event. Even if upfront emissions are our priority, we should know that our choices today do not have negative unintended consequences in only 20 or 40 years.

Not taking a holistic WLC view can be seen as kicking the carbon can down the road with the resulting consequences. Further, failure to consider in detail the end of life phase of a project from the outset means that ideas such as designing for future disassembly and circularity become of minor interest.

Deteriorating buildings lead to the deferred carbon costs of extensive retrofits, or demolition and new build. The seriousness of climate change means that we need to chase down and deliver carbon reductions across all aspects of a building’s life right now.

We should of course continue to provide limits for upfront carbon and energy use, but in the context of WLC limits. The RICS professional standard “Whole-life carbon assessment for the built environment 2nd edition” (RICSPS) deals with the inaccuracies around assessment by including a split contingency specifically to deal with uncertainty. This is made up of three parts: a contingency factor based on the following components; project phase, a carbon data uncertainty factor, and a quantities uncertainty factor.

These together provide a contingency percentage that reduces as a project progresses. This mechanism helps deal with the issues of inaccurate data. The RICSPS also provides default lifespan figures as an aid to consistent reporting.

Alternatively there are tools such as Niscai, (I am an advisor) which mines millions of data sets of in-use building products to provide designers with much more accurate WLC data. Instead of guessing 20-25 years life span for a fancoil unit and applying generic carbon performance, the tool will pull up a range of fancoil units with their actual in-use CO₂ and ££ costs including energy use, plus their upfront CO₂ and ££ costs.

We need to ensure that our design culture evolves so that carbon reduction is as embedded as gravity or sunlight. This means significant behavioural change and the development of a carbon intuition across the project team

This means your WLCA can use actual product data with a significant improvement in both in-use and upfront accuracy. This is happening now.

It is not just getting the numbers right that is the issue. We need to ensure that our design culture evolves so that carbon reduction is as embedded as gravity or sunlight. This means significant behavioural change and the development of a carbon intuition across the project team.

NZCBS has started the consistency process by providing reliable upfront carbon and energy use limits and a verification process, and as the standard states this will include limits for WLC when the data is sufficiently reliable. I would suggest that we have already reached this point.

There are uncertainties about all lifecycle stages, but that does not mean we should not have limits. Limits provoke action and influence behaviour. I would therefore advocate including WLC limits, either by the GLA commissioning NZCBS to provide them, or by convening a panel of experts to do it.

Simon Sturgis is an architect and founder of Targeting Zero, the carbon consultancy