Part Z – a phased approach to limiting embodied carbon

There is a proposed change to UK Building Regulations 2010 on the table. Part Z is a proof-of-concept amendment designed to report and limit the use of the embodied carbon.

Why does this need to happen?

The construction sector contributes a substantial proportion of carbon emissions. According to a report by the United Nations Environment Programme, construction accounted for 38% of total global energy-related CO2 emissions in 2019, the most recent year for which we have data. There are two aspects to this: operational carbon emissions (from energy and water use) and embodied carbon emissions (from construction materials).

Embodied carbon has been or is about to be limited in a number of other countries, too: in the Netherlands since 2018, and scheduled to happen in Denmark, Sweden, France and Finland between 2023 and 2027. It is currently happening in three of the US’s fifty states. Given the RICS professional statement Whole Life Carbon for the Built Environment has been the de facto standard on the topic since 2017, it should be easier to do here, if anything.

Of course, the big picture, as laid out in the 2015 Paris Agreement, is limiting the rise of global temperatures by 2 degrees Celsius; preferably, 1.5. To do this, we need to get to net zero by 2050, and prior to that, there is the first step of halving greenhouse gases (GHGs) by 2030. This requires a high degree of decarbonisation.

21st century changes

Historically, operational carbon formed the majority of most buildings’ emissions, but this has changed since the turn of the century due to renewables and, more generally, building becoming significantly more efficient to operate. Why is this? As stated in a recent article,

“this increase in operational efficiency is partly due to the 2006 overhaul of Building Regulations Part L and the tightening of its emissions limits that followed. Architects and engineers have been driven to design more energy-efficient buildings: questioning the best orientation for the scheme, adding passive measures such as improved insulation and airtightness, and capturing and reusing waste heat.”

However, it’s not quite the same story with embodied carbon. It has risen during the same period; even in a building that has been well-designed, embodied carbon emissions constitute over 50% of a building’s expected emissions during its predicted lifetime. Moreover, much of it is released during the construction period. This is the context for the proposed regulation change.

Photo: Jonymamilou/cropped from original/licensed under CC BY 2.5

The proposal

What is being put forward is that embodied carbon should be assessed on all projects, as part of a comprehensive whole life carbon assessment; and not assessed, but capped. It is all explained in Approved Document Z, which “is aligned with the Royal Institution of Chartered Surveyors (RICS) Professional Statement ‘Whole life carbon assessment for the built environment’, and guidance and recommendations made by the Royal Institute of British Architects (RIBA), the Institution of Structural Engineers (IStructE), the Chartered Institution of Building Services Engineers (CIBSE), the UK Green Building Council (UKGBC) and the London Energy Transformation Initiative (LETI).”

There are stages to implementation, with carbon assessment (Requirement Z1) for buildings other than dwellings scheduled from January 2023, for dwellings from January ’25 and carbon intensity (Requirement Z2) applied to all buildings from two years on from that. Some more detail:

·         Z1 - Whole life carbon emissions shall be assessed and reported for the building and any other parts of the project where Building Regulations apply

·         Z2 - Reasonable provision shall be made for the minimisation of carbon emissions

This is the intention behind them:

“Part Z1 is intended to normalise the use of whole life carbon assessments within the building design process, enabling design teams to identify ways in which to reduce the whole life carbon impact of the building. Assessment data will also be used to determine national targets for embodied carbon that will be used for Part Z2. Part Z2 is intended to discourage excessive and unnecessary use of resources within the built environment, by setting a reasonable standard of efficiency for the upfront embodied carbon intensity of the building.”

This all seems very sensible and clear.

Whole Life Carbon

It is all predicated upon a Whole Life Carbon (WLC) assessment, which tests the carbon emissions that result from the combination of the materials, construction and use of a building throughout its life and afterlife, effectively, as demolition and disposal form part of the cycle. The assessment considers operational (both regulated and unregulated) and embodied emissions in tandem over a project’s life cycle, and determines the best opportunities to reduce lifetime emissions. 

This dual approach, which pays attention to the carbon intensity of the structure itself as well as to reducing its operational energy, is part of the move away from simply focusing on operational emissions discussed above. The RICS guidance uses the following example to illustrate the potential pitfalls of focussing solely on the operational side:

“The embodied carbon burden of installing triple glazing rather than double can be greater than the operational benefit resulting from the additional pane.”

Of course, given that WLC assessments have been around for a while, many in the construction industry are already measuring embodied carbon. For example, the London Plan requires it.

For the purposes of Part Z, operational energy (WLC module B6) is not assessed, though operational carbon is, as is sequestered carbon (and, obviously, embodied). Upfront embodied carbon cannot exceed upfront embodied carbon limits, and this must be demonstrated from the outset via the preliminary WLC assessment. This means that projects must get on the good foot from the start, which minimises the chances of the finished project having little relationship to what was planned in embodied carbon terms. The details regarding these limits are outlined in a table in the Part Z proposal.

It’s a hugely important step, so let’s hope it gets approved. As Will Arnold, head of climate action at the Institute of Structural Engineers, argues

“The adoption of Part Z would do for embodied carbon what Part L did for operational carbon: it would represent a show of government commitment that would give industry the confidence to invest in innovative low-carbon materials and products, alongside cleaner and more efficient methods of construction. It would transform the industry into one that saves our precious resources, rather than squandering them.”

Industry needs to know that its financial commitments are backed up, essentially; Part L will do that. As part of that, Part Z is getting supporting statements from major players in the field, which can be read here.