Posted by Rayan Azhari

The UK Net Zero Carbon Buildings Standard - Part 2: Benefits and Considerations

The UK Net Zero Carbon Buildings Standard (NZCBS) provides two distinct pathways for an existing building to achieve its operational energy targets: "Step-by-Step Retrofit" and "One-Go Retrofit." The choice between these approaches has significant implications for project timelines, financial planning, and the overall sustainability strategy for the building. This article examines the benefits, considerations, and requirements associated with each pathway to help building owners make informed decisions.

One-Go Retrofit: Immediate compliance with locked-in limits

Definition: A "One-Go Retrofit" is a comprehensive renovation project. It brings a building's energy performance up to the Standard's requirements at a point in time in a single intervention. This approach typically involves significant upgrades to the building fabric, including insulation, windows and building services.

Benefits:

  • Immediate and permanent compliance: On completion, the building immediately conforms to the standard's "One-Go Retrofit" energy limits. These are then "locked in" for the building's lifespan. This provides instant recognition of improved energy performance and a potential competitive advantage.
  • Certainty and simplicity: The One-Go approach offers a clear, defined endpoint for compliance. Once achieved, no further improvements are required to maintain compliance. This simplifies long-term planning but may need a "deeper" retrofit than the initial stages of a Step-by-Step approach.

Whichever pathway is chosen, a building’s compliance with operational energy limits must be verified annually.

Step-by-Step Retrofit: Phased approach with limits continually becoming tighter

Definition: A "Stepped Retrofit" allows for a phased approach to achieving the Standard's energy targets. Buildings can initially comply with more lenient limits than the One-Go limit at the time but must gradually improve their performance through a series of planned interventions. Eventually, they will likely exceed the One-Go limit if that was chosen at the start.

Benefits:

  • Flexibility and cost management: Spreading retrofit works over time can make financial planning more manageable, especially for large or complex buildings. This phased approach allows building owners to prioritise interventions based on budget availability and potential disruption to occupants.
  • Lower initial carbon impact: Implementing energy efficiency measures incrementally can distribute the upfront embodied carbon impact over a longer period. This can potentially reduce the initial carbon footprint, though the cumulative impact may be similar or even greater than a One-Go approach.
  • Adaptability to technological advancements: A phased approach provides the opportunity to incorporate newer, more efficient technologies as they become available. This can result in a more optimised and future-proofed solution. However, by delaying implementation, the measures likely have to go further eventually.

Requirements for Step-by-Step Retrofits:

To pursue the "Step-by-Step Retrofit" pathway, building owners must submit a comprehensive Retrofit Plan that includes:

  • Detailed scope of works: A clear description of the fabric and services upgrades for each stage.
  • Robust energy performance modelling: Calculations demonstrating compliance with the 2040 operational energy limit and any applicable interim limits. These calculations should employ robust energy performance modelling, exceeding basic building regulations compliance.
  • Life cycle embodied carbon assessment: An assessment of the embodied carbon of the retrofit works, ensuring compliance with upfront carbon limits for each project phase.
  • Timeline and Commitment: A detailed timeline for each stage, with a firm commitment to achieving the 2040 target.

Is the "Step-by-Step" route the right choice?

The decision of whether to pursue a "Step-by-Step" or "One-Go Retrofit" depends on several factors specific to the building and its ownership:

  • Budget and financial planning: One-Go Retrofits require more significant upfront investment, while Step-by-Step Retrofits allow for some cost spreading. However, most buildings will require significant activity at the time it is decided to comply with the Step-by-Step pathway. For example, an office building aiming for compliance in 2025 must achieve an EUI of 120 kWh/m2 GIA/year under the Step-by-Step pathway, and then improve to 90 kWh/m2 GIA/year by 2032 and 55 kWh/m2 GIA/year by 2040.

    If the One-Go path is chosen, the limit is 100 kWh/m2 GIA/year if done in 2025, 85 if done in 2030, and 70 kWh/m2 GIA/year if left to 2035 (with other numbers in between).

    By 2040 the limit for both pathways is the same (if compliance is left until then). Therefore, while offering flexibility, the Step-by-Step path does not necessarily reduce the overall investment required.

  • Building complexity and occupancy: Large, complex or continuously occupied buildings may benefit from the phased approach of a Step-by-Step Retrofit. This can minimise disruption. However, one may prefer to wait until all tenant leases have expired and then conduct a One-Go retrofit as part of a major refurbishment.
  • Urgency of compliance: Owners seeking immediate recognition and market advantages may opt for the One-Go Retrofit approach to achieve immediate and permanent compliance.
  • Long-term vision and sustainability goals: A Step-by-Step Retrofit can align with a long-term vision for ongoing energy efficiency improvements, incorporating future technological advancements. This requires careful planning and a steadfast commitment to the final target.

Conclusion

Both pathways will typically present challenging routes to achieving net-zero carbon for existing buildings. The optimal choice depends on a thorough assessment of the building's unique characteristics, the owner's financial capacity and their long-term sustainability objectives.

While the "Step-by-Step Retrofit" may provide more flexibility and potentially lower upfront carbon, the "One-Go Retrofit" provides the comfort of continuing future compliance and clear market recognition.

The most successful strategies will be those that are carefully planned, executed and aligned with a comprehensive vision of net zero for the built environment. Choosing wisely between these pathways is not just about meeting a standard; it's about making a strategic commitment to decarbonisation and contributing to a more sustainable future.