GRI Report Assurance
GRI assurance is voluntary — unlike CSRD which mandates it. But investor expectations, CDP requirements, and ESG rating agency scoring increasingly treat assured GRI reports as the standard. Understanding what GRI assurance covers and how to obtain it is essential for credible reporting.
GRI assurance is voluntary — unlike CSRD which mandates it. Two assurance standards are commonly used for GRI reports:.
GRI assurance standards — ISAE 3000 vs AA1000AS
Two assurance standards are commonly used for GRI reports:
ISAE 3000 (Revised) — International Standard on Assurance Engagements: The accounting profession's standard for non-financial assurance. Used by Big Four and national audit firms. Familiar to finance teams. Provides limited or reasonable assurance conclusions.
AA1000AS v3 — AccountAbility Assurance Standard: A stakeholder-focused assurance standard developed specifically for sustainability reporting. Assesses adherence to AA1000 principles (inclusivity, materiality, responsiveness, impact) as well as accuracy of data. Used by specialist sustainability assurance providers.
Both are recognised by GRI. ISAE 3000 is more familiar to financial auditors; AA1000AS provides deeper assessment of stakeholder engagement and materiality process quality.
What GRI assurance covers
GRI assurance scope varies by engagement. Common scope options:
Full report assurance: All GRI disclosures in the report are subject to assurance procedures. Highest credibility, highest cost.
Selected disclosure assurance: A defined subset of disclosures — typically GHG emissions, health and safety metrics, and water data. Balances credibility with cost.
GRI Content Index verification: Third-party verification that the Content Index correctly maps disclosures to report locations and that omissions are properly explained. Lower cost, focuses on completeness rather than accuracy.
For companies preparing for CSRD: obtaining GRI limited assurance now builds internal capability, data documentation, and assurer relationships before CSRD mandatory assurance kicks in.
The assurance market for GRI reports
GRI assurance is provided by two main provider types. Big Four and national audit firms: typically use ISAE 3000, audit-methodology approach, familiar to boards and audit committees. Pricing tends to be higher.
Specialist sustainability assurance providers: Bureau Veritas, SGS, LRQA, DNV, ERM, Deloitte Sustainability. Often use AA1000AS or ISAE 3000. Deeper sustainability expertise, sector-specific knowledge. Pricing varies widely.
For CSRD Wave 2 companies: consider using the same provider for GRI assurance (2025/2026) and CSRD assurance (from 2028). This builds the provider's knowledge of your business and reduces cost and friction for the mandatory CSRD engagement.
Frequently asked questions
Does obtaining GRI assurance reduce my CSRD assurance costs?
Yes — if you use the same provider. The provider builds knowledge of your data systems, methodology, and internal controls during GRI assurance. For the CSRD engagement, this prior knowledge reduces the scoping and testing work required, typically reducing first-year CSRD assurance costs by 15–25%.
What level of assurance do investors expect for GRI reports?
Investor expectations vary. Institutional investors with ESG mandates increasingly expect limited assurance at minimum for GHG emissions. Full report reasonable assurance is rare for voluntary GRI reports but is growing in frequency among FTSE 100 and DAX 40 companies.
Can we self-declare GRI alignment without assurance?
Yes — GRI alignment (reporting with reference to or in accordance with GRI Standards) does not require external assurance. Self-declaration is valid. However, unassured GRI reports receive lower credibility scores from ESG rating agencies and may not satisfy investor due diligence requirements.