The evolving assurance landscape for GRESB submissions

As companies progress on GRESB reporting, the focus increasingly shifts from how data is collected to how its quality and credibility are demonstrated. A strong operating model creates the foundation for consistent data collection, governance, and submission at portfolio scale—but that foundation must be matched by a clear approach to assurance.

This article examines the evolving role of assurance in GRESB submissions. It covers how assurance has moved from a voluntary validation exercise to a recognized component of the assessment framework, how it is reflected in scoring for both Real Estate and Infrastructure, what standards are commonly applied, and how organizations can use assurance to strengthen data quality, governance, and long-term reporting resilience.

When GRESB was first established, assurance played a limited role in submissions. ESG data was primarily self-reported, and assurance, where applied, was typically voluntary, selective, and focused on a narrow set of environmental metrics. At that stage, it supported internal validation and emerging ESG practices rather than serving as a formal benchmarking input.

Over time, several converging pressures changed this. Investor demand for reliable, comparable ESG data grew significantly, as did regulatory expectations around non-financial reporting. Participants expanded across geographies and asset classes, making data consistency and comparability a necessity across portfolios. At the same time, ESG disclosures became more consequential—feeding into investment decisions, capital allocation, and public reporting, raising the stakes for data credibility.

As a result, assurance evolved from an optional enhancement into a recognized mechanism for strengthening data quality within the GRESB framework.

Assurance is now an established and structured element of the GRESB Assessments—recognized not only as a marker of good practice, but as a formal mechanism to support data quality, consistency, and credibility across submissions. Within the framework, assurance refers to the independent verification or assurance of ESG data and related processes carried out by a third party. Its role is to provide confidence that reported information is grounded in robust systems and can be relied upon for benchmarking and decision-making.

GRESB applies assurance in a focused manner, concentrating on data areas most relevant to performance measurement while recognizing differences in asset class, materiality, and operational context, rather than imposing uniform requirements across all indicators.

In practice, assurance supports GRESB’s objectives in four key ways.

1. Supporting data reliability and comparability
   GRESB relies on ESG data that is comparable across participants, asset classes, and regions. Assurance reinforces this by confirming that reported data is derived from verifiable source information, that calculations are performed using documented and consistently applied methodologies, and that assumptions and boundaries are clearly defined. This supports fair and meaningful comparison across participants within the benchmark.
   
2. Reinforcing governance and process maturity
   Beyond individual data points, assurance provides insight into the processes and controls that underpin ESG reporting. In a GRESB context, this includes whether organizations have clear ownership of ESG data, defined review and approval processes, and documented procedures for data collection and consolidation. These elements are increasingly important as ESG information becomes more embedded in organizational decision-making and external reporting obligations.
3. Linking assurance to measurable assessment outcomes
   A defining feature of the current GRESB framework is that assurance is no longer treated as contextual information alone. It is explicitly recognized within the scoring methodology, particularly for environmental performance data. By linking assurance to specific indicators and point allocations, GRESB reinforces the role of independently reviewed data in supporting credible benchmark outcomes and encourages participants to integrate assurance into their reporting cycles in a structured and consistent way.
   
4. Scoring recognition
   Assurance is explicitly recognized within GRESB’s scoring methodology, with defined point allocations by asset class.In the Real Estate Assessment, assurance is directly linked to environmental performance indicators. Up to 5.5 points of the total GRESB Score are awarded when energy, GHG emissions, water, and waste data are externally assured. These points sit within the Performance component of the assessment.In the Infrastructure Assessment, assurance has a direct impact on GHG indicators, increasing the score by up to 25% of the GH1 indicator, based on the materiality of GHG to the entity.

GRESB does not prescribe a single assurance standard but recognizes various globally established standards. It expects assurance to be independent, systematic, and defensible, with clear documentation provided as part of the submission. A full list of accepted assurance schemes is published by GRESB and should be consulted when selecting a provider or planning an engagement.

In practice, three international standards are most commonly applied.

• AA1000AS is widely used where the assurance scope extends beyond individual data points to cover ESG processes, governance arrangements, and management systems. It is particularly relevant for organizations seeking a broader review of their reporting framework alongside supporting data.
• ISO 14064 and ISO 14065 are the principal standards for greenhouse gas emissions verification, covering organizational boundaries, calculation methodologies, and emissions data. They are especially relevant for infrastructure assets seeking assurance of Scope 1 and Scope 2 emissions under GH1.
• ISAE 3000 (Revised) is the general assurance standard provided by the International Auditing and Assurance Standards Board for non-financial information. It provides a structured framework for planning engagements, gathering evidence, and forming conclusions, and is often applied where assurance forms part of a broader sustainability report or annual reporting exercise.

Choosing between these standards depends primarily on scope and provider and is not differentiated in terms of recognition or scoring by GRESB. In some cases, engagements may reference more than one standard where both process-level and data-level assurance are required. ISSA 5000, published by the IAASB in November 2024 and effective from December 2026, is set to replace ISAE 3000 (Revised) as the global baseline for sustainability assurance. Organizations should factor this transition into their assurance planning.

Within the Real Estate Assessment, assurance is recognized across five specific indicators spanning both the Performance and Management components.

• MR1: External review of energy data — 1.75 pts
• MR2: External review of GHG data — 1.25 pts
• MR3: External review of water data — 1.25 pts
• MR4: External review of waste data — 1.25 pts
• RP1: ESG reporting (if integrated report is assured) — up to 1.17 additional pts

In total, assurance and verification can contribute up to 6.67 points to the overall GRESB Real Estate score.

Organizations that prepare early for assurance engagements are better placed to avoid delays and achieve stronger outcomes. In practical terms, this means having the following in place before an engagement begins.

• A clear data trail from source records through to reported figures, with no unexplained gaps or undocumented adjustments.
• Documented methodologies covering how data is collected, consolidated, and calculated—including any estimation approaches used.
• Defined data ownership, with named individuals responsible for each data stream and a clear sign-off process.
• Supporting evidence organized and accessible, including utility bills, meter readings, invoices, or other primary source documentation.
• Agreed scope and boundary definitions, covering which assets, facilities, and activities are included in the reported figures.
• An independent assurance provider. GRESB requires that any recognized scheme demonstrates independence, ensuring the third party has no conflict of interest with the reporting entity.

As assurance becomes more embedded in the GRESB framework, the credibility of the engagement itself matters as much as its scope. GRESB requires that any recognized assurance or verification scheme demonstrates independence, competency, and a clear methodology. Organizations that select providers carefully, with these criteria in mind, will be better placed to meet GRESB’s expectations and demonstrate the reporting integrity that investors increasingly expect.

This article was written by Vishal Goel, Director ESG; Navneet Jain, Consultant—ESG & Sustainability; B Siddharth, Consultan—ESG & Sustainability at Earthood Services Limited. Learn more about Earthood Services Limited here.