The UK Net Zero Carbon Buildings Standard Guide: Part 2: Embodied carbon

MEng
Senior Sustainability Consultant
Table showing elements of the UK NZC Buildings Standard

The pilot version of the UK Net Zero Carbon Buildings Standard (the Standard) was published in September 2024. The full document can be downloaded here.

The Standard has been produced by a range of industry professional organisations including RIBA (architecture), IStructE (structural engineering), CIBSE (services engineers) and RICS (surveyors), along with a large team of other industry organisations and professionals. 

It aims to set out unambiguously, for a wide range of scenarios, the characteristics that buildings and building projects need to be aligned with the UK’s strategy to become net zero carbon by 2050. The Standard builds upon and supersedes previously published approaches such as the UKGBC Net Zero Carbon Building Framework, the RIBA Climate Challenge and the various LETI design guides.

Read more from our guide: 

Part 1: Key principles and overview 

Part 2: Embodied carbon

Part 3: Operational energy

Part 4: On-Site renewable generation

Part 5: Operational Water Use

Part 6: Fossil fuel free

Part 7: Electricity demand management 

Part 8: District heating and cooling networks

Part 9: Space heating and cooling

Part 10: Refrigerants 

Part 11: Carbon offsetting

1. Embodied Carbon approach and targets

As an industry, and as a practice, we've spent decades improving our designs to achieve extraordinary reductions in operational energy. However, it was only recently that the industry started to pay attention to the impacts of embodied carbon and this, coupled with challenging targets, will likely present the biggest hurdle to overcome for most schemes as we adapt to new ways of building.

The pilot of the Standard provides a set of prescriptive Embodied Carbon limits for a range of building types and project scenarios.  The main features provide targets for approximately 30 building types or subtypes.

There are three types of targets:

  1. New works
  2. Retrofit works
  3. Reportable works

Broadly speaking, the Embodied Carbon modelling is in line with RICS Professional Standard (Whole-life Carbon Assessment for the Built Environment, version 2). However, there has been a reasonably significant uplift in additional processing and reporting when compared to a simple RICS WLCA model.

A bar chart showing embodied carbon targets for various types of projects starting on site from 2028

2. Comments on the proposals

We suspect that the feasibility of achieving NZC standards for many projects will depend on the impact of embodied carbon. 

Every project is of course unique in its challenges, but we expect the following to be broadly true: 

A table demonstrating the level of difficulty with achieving the NZC Buildings Standard from deep retrofit up to new build.

In general, embodied carbon design guidance will be crucial to every typology and type of build. Some examples of this are shown below:

  • Re-use will make everything easier, and must be a priority for existing buildings.
  • Minimising grid spacing, starting at 7.5m for offices, and 4.5-6.5m for residential
  • Challenging expected norms within the industry: 
    • No basements
    • No transfers, unless short-span and unavoidable
    • Floor zones that accommodate structural efficiency, not minimum depth.
  • Facades will emerge as even more of a hot-spot than they already are:
    • Lightweight is a good starting point. Heavy facades will add complexity to light/thin structures.
    • Optimising, rather than maximising glazing. The in-life replacement of glass within Insulated Glazing Units (IGU) causes a large uplift in carbon, although this is more pronounced for ‘whole-life’ carbon.
    • Complexity in façade form typically creates complexity in façade sub-structure. This area is a carbon hot-spot (typically aluminium framing) and complex façade forms could tip the balance the wrong way, while simpler forms provide a better foundation.
  • Building services are historically under-reported and we expect the upfront embodied carbon of this category to keep increasing year-on-year. 
    • We must be wary of minimising upfront embodied carbon at the expense of significant in-use emissions i.e. VRF/VRV refrigerant leakage impacts.
    • Whole-life carbon early studies on systems and elements, such as heat pumps, must be undertaken to ensure a holistic carbon view can be achieved. 

3. Practical changes to project running

We believe that following elements will be pivotal to practically achieving net zero carbon on projects:

  • Golden thread approach, continuing embodied carbon oversight from stages 1-6 (net zero carbon co-ordinator role).
  • Early client briefing (ideally during stage 1) to explain the detail of UK NZC BS process and the likely differences to business-as-usual design.
  • Early embodied carbon advice from experienced and holistically minded professionals will pay dividends (net zero carbon co-ordinator roles). The more barriers that can be removed early on, the better the chances the project brief will provide the right direction for success.
  • Main barriers to success will probably not be technical. The following parties need to be included early in the process and given space to influence and buy-in to the design, without a large uplift in upfront carbon:
    • Estate Agents
    • Insurers
    • Contractors
    • Cost Consultants

4. Challenges and cautionary advice

  • We need to be wary of turning to timber as a panacea. Judgement needs to be applied that the proposed solution is an appropriate use of timber; in terms of material volume-per-m2-provided and playing to timber’s material strengths.
  • We must avoid ‘gaming-the-system’ with ineffective low-carbon specification options i.e. high GGBS cement replacements, electric arc furnace steel, high recycled content aluminium. The scarce-resource principle must be applied to understand if a specification will be a ‘net-reduction’ to atmospheric carbon.
  • Supply chain decarbonisation (pivotal to future targets) may not keep pace with targets, but future iterations of the standard will address this if such realities present themselves.
  • Some methods of Embodied Carbon modelling, namely the CWCT Standard and TM65, tend to result in larger upfront carbon contributions than historic, less scientific forms of modelling. These new methods may pose challenges with respect to ‘expected contributions’ from façade and building services.

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