EN 1090 Execution Classes: A Fabricator’s Guide to EXC1–EXC4

Execution classes are where structural steel contracts quietly go wrong. A two-character code on a drawing — EXC2, EXC3 — carries an entire quality regime: welder qualifications, procedure qualifications, NDT percentages, traceability, documentation. Price a job at EXC2 that turns out to be EXC3 and the margin is gone; fabricate at the wrong class and the steel may not be legally supplied. Here is the system, decoded.

What an execution class is

EN 1090-2 (technical requirements for steel structures) grades fabrication requirements into four execution classes, rising with the consequence of failure and the demands of the structure:

Class	Typical territory	Regime
EXC1	Low-consequence structures — minor agricultural, temporary works	Lightest requirements
EXC2	The default for ordinary predominantly static building structures	The common commercial baseline
EXC3	Higher-consequence or fatigue-loaded structures — bridges, cranes, key public buildings	Substantially tighter welding, NDT and traceability
EXC4	Extreme-consequence structures	The most onerous, specified rarely and deliberately

The designer sets the class (per structure, or even per component or detail). If the drawings are silent, do not guess quietly: raise an RFI. EXC2 is the widely applied default for ordinary building structures, but “the drawings didn’t say” has never survived a dispute.

What rises with the class

The execution class scales four things fabricators pay for:

1. Welding quality management. EN 1090-2 anchors welding to the ISO 3834 series — comprehensive-to-elementary quality requirements depending on class — plus welding coordination with competence appropriate to the work.
2. Qualification. Welding procedures qualified (ISO 15614-1) and welders certified (EN ISO 9606-1), with scope matched to the joints actually fabricated.
3. Inspection and NDT. Visual inspection of all welds, plus supplementary NDT (MPI, DPI, UT as applicable) to extents that increase with execution class and joint type — performed by qualified NDT personnel.
4. Traceability and documentation. Material certificates, weld records and inspection results — the audit trail deepens as the class rises.

None of this is optional decoration: it is what the CE mark attests.

CE marking: the legal layer

Structural steel components are construction products. Under the Construction Products Regulation, fabricators supplying them in Ireland and across the EU must CE mark to EN 1090-1 — which requires a certified factory production control (FPC) system, assessed by a notified body, covering the execution classes the fabricator produces.

Two practical consequences:

• A fabricator’s FPC certificate states the classes it may declare. Producing EXC3 work on an EXC2 certificate is non-conformity, however good the welding.
• The welding chain — procedures, welder certificates, coordination, NDT — is the core of what the FPC audit examines. Weakness there is the most common audit finding.

Metlab supports this chain end to end: as an INAB-accredited certification body (ISO/IEC 17024) we qualify the welders; our laboratory tests the procedure qualification coupons; our CSWIP-qualified inspectors and certified NDT technicians cover production inspection; and our INAB-accredited laboratory (ISO/IEC 17025) gives the results standing an FPC auditor accepts without argument.

The pre-contract checklist

Before pricing or accepting structural steel work:

• Find the EXC statement. Per structure and per detail — mixed classes on one job are legitimate and common.
• Check your FPC coverage. Certificate class ≥ contract class, including any subcontracted welding.
• Map the qualification gap. Which joints need procedures or welder ranges you do not yet hold? Qualification lead time belongs in the programme, not the panic phase.
• Price the NDT honestly. The class dictates extent; an EXC3 NDT schedule priced at EXC2 rates is a loss booked early.
• Agree documentation on day one. The handover file is defined by the class — retrofitting traceability is the most expensive way to compile it.

Where fabricators actually stumble

From our inspection work across Irish fabrication: welder certificates with lapsed six-month confirmations; procedures qualified years ago that do not cover a new joint configuration; NDT done but by personnel without the right method certification; and material traceability that dissolves at the subcontractor boundary. Every one is cheap to prevent and expensive to discover during a client audit.

Metlab keeps fabricators audit-ready — welder and procedure qualification, production NDT and independent inspection, from Cork and Dublin. Send us your current certificate matrix and we’ll tell you where the gaps are.