How the Verification Process Works
From initial scope clarification to ZF-compliant verification report. Our supply chain sustainability audit process helps you choose between ISRS 4400 and ISAE 3000.
Verification Options
ZF accepts multiple verification levels. The right choice depends on whether the verification is only for ZF or also for other customers.
ISRS 4400
Agreed-Upon Procedures
We perform pre-defined procedures on your certificates and report factual findings — no opinion expressed. Typically 2 auditor days. Suitable for the ZF Recommendation level. Under the ZF Minimum Requirement, ISRS 4400 may also qualify for straightforward cases — but only after a prior complexity assessment; where the allocation is too complex, limited assurance is required instead. We run that assessment with you in the free scoping call. Certificates must be retired with a ZF production reference.
Book Free ConsultationISAE 3000
Limited Assurance
Full sustainability assurance — we express a conclusion on your renewable energy claims. Always accepted for the ZF Minimum Requirement (mass balance, dedicated meter), and required wherever the prior assessment shows the allocation is too complex for ISRS 4400. Also the right choice if the report serves other customers. Internationally recognized Scope 2 standard.
Book Free ConsultationRealistic Timeline
The actual duration depends strongly on the availability of contacts and documents.
Scope Clarification
Which entities, which plants, which approach. Identifying the right contractual partner.
Contract & Kickoff
Authorized signatory signs engagement letter. Kickoff meeting. Tailored document checklist.
Verification & Report
Document review, completeness declaration, formal verification report. Certificate retirement with ZF production reference in the registry.
Early Start Possible
Engagement and scope clarification can start as early as November. When documents (GOs, consumption data) arrive from January onward, only the verification step remains — well ahead of the 31 May deadline.
When Should You Start?
ZF's verification deadline is 31 May of the year following the reporting year (e.g. 31 May 2027 for reporting year 2026). The earlier you start, the smoother the process.
Q4 (Oct to Dec)
Set up engagement and define scope before year-end.
January to March
Documents become available. GO cancellation statements arrive. Enough time for full verification.
April to May
Deadline is 31 May of the following year. Still, avoid a last-minute start — missing documents cost time you no longer have.
Not Sure Which Approach You Need?
Book a free 30-minute consultation. We assess your situation and recommend the most efficient approach.