ESRS S1 Assurance
ESRS S1 workforce disclosures are subject to mandatory limited assurance — making them legally binding statements subject to professional verification. Understanding how assurers approach S1 data, what evidence they require, and where common findings occur enables companies to prepare effectively and avoid last-minute surprises.
ESRS S1 workforce disclosures are subject to mandatory limited assurance — making them legally binding statements subject to professional verification. Limited assurance provides a negative assurance conclusion — the assurer states that nothing has come to their attention that causes them to believe the sustainability information is materially misstated.
How limited assurance works for ESRS S1
Limited assurance provides a negative assurance conclusion — the assurer states that nothing has come to their attention that causes them to believe the sustainability information is materially misstated. This is a lower standard than reasonable assurance (used for financial statement audits) but still requires substantial evidence collection.
For ESRS S1, assurance procedures typically include: inquiry of management responsible for each S1 metric (HR, H&S, Finance, Legal); analytical procedures — comparing S1 metrics to prior year, industry benchmarks, and internal consistency checks; inspection of source documents — sample testing of HRIS extracts, payroll records, H&S incident registers, and LMS records; recalculation of derived metrics — TRIR, gender pay gap ratio, CEO pay ratio, average training hours; and review of methodology documentation — confirming that definitions and calculation approaches are consistent with ESRS requirements.
Materiality threshold: Assurers apply a materiality threshold below which errors are not reported. For S1 quantitative metrics, typical materiality thresholds are 5–10% of the reported value for financial metrics (pay gap, CEO ratio) and 5% for H&S rates. Errors below materiality are noted to management but do not affect the assurance conclusion.
Scope: The assurance covers all mandatory ESRS S1 disclosures in the sustainability report — both quantitative metrics and qualitative disclosures. Assurers assess whether qualitative process descriptions are consistent with their quantitative evidence — a company claiming a robust H&S management system but showing high injury rates and incomplete audit trails creates a qualitative-quantitative inconsistency that assurers investigate.
Common S1 assurance findings from Wave 1
Wave 1 CSRD assurance engagements identified recurring S1 findings that Wave 2 companies should proactively address:
Finding 1 — Non-employee worker data incomplete: The most universal finding. Companies disclosed employee H&S metrics (S1-14) but could not provide supervised worker data — or disclosed supervised worker data without adequate source documentation from agencies and contractors. Preventive action: build contractor H&S incident reporting into agency contracts and conduct pre-assurance data validation.
Finding 2 — Hours worked calculation inconsistency: H&S rates (TRIR, LTIR) calculated using contracted hours rather than actual hours worked, or using different hours definitions for employee and supervised worker calculations. Preventive action: document the hours calculation methodology explicitly and apply consistently across both populations.
Finding 3 — Gender pay gap methodology unclear: Pay gap calculations that mixed base salary and total compensation without clear documentation, or that excluded certain employee categories without disclosed rationale. Preventive action: document the compensation scope (base only vs total), the exclusions, and the rationale before assurance begins.
Finding 4 — Training hours classification inconsistency: Including meeting time, self-study without structured content, or general orientation as training hours — overstating the metric. Preventive action: define 'training' explicitly (structured content with learning objective) and apply the definition consistently to all training types.
Finding 5 — Discrimination incident count inconsistency: Discrepancy between the HR case management system count and the legal/compliance count — cases managed by legal were not included in the HR total. Preventive action: reconcile HR and legal case registers annually before assurance.
Preparing for S1 assurance — a practical checklist
Assurance preparation for ESRS S1 requires organising evidence in advance — not scrambling to find source data when the assurer requests it.
4–6 months before assurance: Complete the S1 data collection and calculation. Conduct internal variance analysis — compare all metrics year-on-year and document explanations for changes above 10%. Resolve any data quality issues identified. Brief the HR director, H&S director, finance director, and chief legal officer on the assurance process and their role.
2–3 months before assurance: Prepare the S1 evidence pack — organised by metric, with source data extracts, calculation workbooks, and methodology documentation for each. Conduct a pre-assurance readiness review — either internal (using a checklist against ESRS S1 requirements) or using external specialist support to identify and close gaps before the assurer arrives.
During assurance: Designate a single point of contact for S1 queries — typically the sustainability reporting manager. Ensure subject matter experts (CHRO, H&S Director, FD) are available for inquiry sessions. Respond to assurer requests within agreed timelines — delayed responses extend the assurance timeline and create filing deadline risk.
After assurance draft findings: Review findings carefully. Distinguish between: factual errors (correct the data); methodology disputes (engage the assurer with documented rationale); and scope limitations (where data is genuinely unavailable, ensure limitations are transparently disclosed). For any finding that would result in a qualified opinion, escalate immediately to the CFO and board — a qualified opinion on the first CSRD report is a significant governance issue.
Frequently asked questions
Can the same firm provide both CSRD advisory and assurance for our S1 disclosures?
No — independence rules prohibit the same firm (and in most interpretations, the same network) from providing both advisory on the preparation of sustainability disclosures and assurance over those disclosures. Ensure your sustainability consultant and assurance provider are independent. This is the same independence principle that applies to financial audit and advisory services.
Will assurers test individual employee records or only aggregate data?
Limited assurance typically tests at an aggregate level — sampling source data to verify aggregate figures rather than reviewing every individual record. However, for small companies where the aggregate is driven by a small number of records (for example, a company with 5 H&S incidents), assurers may review all underlying records. Prepare source data in a format that allows efficient sample testing — organized HRIS extracts are easier to test than unstructured data.
Our S1-16 CEO pay ratio fluctuated dramatically this year due to LTI vesting — will this cause an assurance finding?
Not automatically — an assurer's job is to verify accuracy, not to assess whether the ratio is appropriate. A high ratio driven by documented LTI vesting events, explained clearly in the report, will be verified and accepted if the underlying calculation is correct. The narrative explanation of the fluctuation — disclosed in the report alongside the ratio — is important context that assurers expect to see for unusual year-on-year movements.