WHAT IS PAS 51215?
PAS 51215 is the UK’s new standard for conducting an Energy & Decarbonisation Assessment. It transforms how large ESOS-qualifying organisations plan and deliver their pathway to net zero.
Developed by BSI and sponsored by the Department for Energy Security & Net Zero, PAS 51215 brings together energy auditing, carbon reduction, emissions analysis, risk and governance evaluation, and net-zero planning into one unified assessment framework.
There are two parts:
- PAS 51215-1: The assessment process
- PAS 51215-2: Competency requirements for assessors and Lead Assessors
Under PAS 51215, organisations must evaluate:
- Energy consumption and related Scope 1 & 2 emissions
- Scope 3 emissions from business travel (minimum requirement), with the option to include a wider Scope 3 boundary
The outputs of the assessment must include:
- A long-term decarbonisation plan
- Prioritised energy and carbon-reduction opportunities
- An implementation roadmap
- Residual emissions estimates
- A review of risks, barriers, and governance
Is PAS 51215 Mandatory?
Not yet, but it will be. For ESOS Phase 4, PAS 51215 is voluntary.
Organisations can choose to follow it or complete a standard ESOS assessment.
From ESOS Phase 5, PAS 51215 (or a fully aligned methodology) becomes mandatory, meaning all large ESOS-qualifying organisations must follow the expanded ESOS structure, including:
- The integrated energy + carbon assessment approach
- Net-zero alignment
- Lead Assessor sign-off
This marks the evolution of ESOS from a set of audits and recommendations to a strategic tool for decarbonisation.
How Does PAS 51215 Work With SBTi?
PAS 51215 directly references the Science Based Targets initiative (SBTi) and acknowledges that many organisations intend to align their decarbonisation plans with science-based pathways.
The standard states that PAS assessments provide:
“a considered and data-driven framework to help organizations working on complementary initiatives such as the UN Race to Zero and the SBTi Corporate Net Zero Standard.”
PAS 51215 supports SBTi readiness by delivering:
- Robust, evidence-based Scope 1 & 2 emissions data
- Identification of emissions-reduction opportunities
- A long-term implementation plan
- Governance and risk evaluation
- A credible decarbonisation pathway
However, PAS 51215 also makes it clear that SBTi requires a broader Scope 3 boundary than PAS 51215’s minimum requirement. SBTi mandates:
- At least 95% of Scope 1 & 2 emissions
- At least 90% of Scope 3 emissions
This means:
PAS 51215 builds the operational foundation, while SBTi validates the targets against climate science.
Businesses aiming for SBTi approval will need to expand the PAS boundary to include all significant Scope 3 categories.
Should Businesses Adopt PAS 51215 Now to Avoid Duplication?
If your organisation plans to implement a net-zero or decarbonisation strategy before the ESOS Phase 4 submission deadline in December 2027, adopting PAS 51215 early is the most efficient and cost-effective route because it avoids future duplication.
If a business produces a net-zero strategy now without using PAS 51215, much of that work may need to be redone in Phase 5 to meet the new requirements. Adopting PAS 51215 now ensures your strategy is already Phase 5 compliant.
PAS 51215 also aligns with the expectations of modern reporting frameworks such as IFRS/ISSB, CSRD, TCFD and CDP, including:
- Risk evaluation
- Governance assessment
This strengthens your wider sustainability and ESG reporting.
Bringing PAS 51215 and SBTi Together
For large organisations that qualify for ESOS and are already exploring or aligning with SBTi, adopting PAS 51215 voluntarily in Phase 4 is a smart, future-proof move. It allows you to build the robust data, governance and decarbonisation groundwork that SBTi expects, while avoiding duplicated effort when PAS 51215 becomes mandatory in Phase 5. Using PAS 51215 now sets your organisation on a clearer, more efficient path to credible, science-aligned net-zero action.
How Earth Hub Supports PAS 51215 and SBTi Alignment
At Earth Hub, our team of qualified ESOS Lead Assessors and decarbonisation specialists are already working with large organisations to build the foundations needed for credible, science-aligned climate action. We support businesses through the full PAS 51215 process, from energy and emissions analysis to developing long-term decarbonisation pathways, while ensuring the outputs align with the expectations of frameworks such as SBTi.
If you’re thinking about aligning with science-based targets, or you want support adopting PAS 51215 for ESOS Phase 4, Earth Hub can guide you through every step. Get in touch to begin building a pathway that’s aligned with both regulation and climate science.