October 21, 2026 · Indumor
If you are asked for an “EXC2” structure, you are being asked for a level of control, not a type of steel. The execution classes of the European standard EN 1090-2 state how tightly fabrication is controlled — materials, welding, tolerances and inspection —; they run from EXC1 to EXC4, and most building and industrial plant structures are fabricated to EXC2, which is also the class that applies when the project does not specify one. The rest of this guide explains why, and what really changes in the shop.
EN 1090 is the European family of standards for the execution of structures. Part 1 sets how the conformity of structural components is assessed — it is the part that enables CE marking in Europe —; Part 2 sets the technical requirements for steel structures; and Part 3, those for aluminum.
The execution class is chosen by the designer, based on three things. The first is the consequences of failure, which EN 1990 classifies from CC1 to CC3: a farm building is not a grandstand. The second is the type of loading, which separates static loads from fatigue or seismic loading, such as a crane runway. The third is the type of production, which distinguishes simple parts from those with more demanding welds or high-strength steels. Those three variables lead to the class: EXC1 for simple, low-consequence structures, EXC2 for most, EXC3 for high consequences or significant fatigue, and EXC4 for structures whose failure would have extreme consequences.
An example makes it concrete. In a warehouse building, with static loads and medium consequences, the result is usually EXC2. If the same building has an overhead crane, the runway — which works in fatigue — may go up to EXC3 even though the rest of the structure stays at EXC2: the standard allows different classes for different components of the same project, and that is what makes sense, because it concentrates control where it is needed.
Each class raises the bar. Welders are qualified to ISO 9606-1 and, from EXC2 up, welding procedures are qualified by testing to ISO 15614-1. The shop needs a welding coordinator with knowledge matching the class, per ISO 14731, and the level of welding quality requirements under ISO 3834 goes from elementary at EXC1 to comprehensive at EXC3 and EXC4. The share of supplementary non-destructive testing grows with the class, material traceability gets stricter, and tolerances are split into essential ones, which affect strength, and functional ones, which affect fit-up and appearance, with two levels of stringency.
In the shop, an execution class shows up in paperwork, hours and people. In paperwork, because every weld has to correspond to a qualified procedure and every welder to a current qualification, and inspection records stop being optional: all of it ends up in the quality dossier. In hours, because every additional test — the ones that look for the welding defects you cannot see —, every dimensional check and every material certificate takes someone's time. And in people, because the welding coordinator is not a decorative title: it is the person who signs that all of that was done.
Tolerances are a good example of the gap between theory and the shop. An essential tolerance, such as the straightness of a column or the squareness of a bearing plate, is not negotiable: the part's capacity depends on it. A functional one, such as the position of a hole for a guardrail, can be specified tighter or looser depending on what gets installed later. Specifying the strictest level everywhere adds cost without adding anything; specifying it where it matters prevents problems at erection.
That is why the class should not be over- or under-specified. Asking for EXC3 for a warehouse mezzanine makes the structure more expensive without making it more useful. Asking for EXC1 for a crane runway, which works in fatigue, is saving in the wrong place. And there is an in-between case that keeps repeating: the drawing says EXC2 because that is customary, but nobody checks whether the shop can demonstrate it.
An execution class on the drawing is worthless if the shop cannot demonstrate it: ask for the qualified procedures, the welder qualifications and, if the structure is going to Europe, the factory production control certificate that CE marking requires.
And how much does a higher class cost? Less than people think in steel, and more than they think in hours. Material and welding are nearly the same; what grows is testing, checks, records and the time of the people who do and sign them. That is why the execution class has to be stated in a request for quotation from the start: two offers for the same structure, one at EXC2 and one at EXC3, cannot be compared. The specification should also state the tolerance class, the extent of testing and who inspects: that way, everyone quotes the same thing.
The documents to expect, depending on the class, are the welding procedures and their qualification records, the welder qualifications, the material certificates, the visual, dimensional and non-destructive testing reports and, for CE marking, the declaration of performance. If a supplier promises EXC2 and cannot show any of those papers, the class exists only on the drawing.
EN 1090 is not mandatory outside the European Union. In the United States, steel structures follow AISC 360 and AWS D1.1, which do not use execution classes; quality is handled through the quality control and quality assurance requirements in Chapter N of AISC 360, which list the inspection tasks for fabricator and owner, the testing called for under AWS D1.1, and fabricator certification programs. In Argentina, the CIRSOC regulations apply — CIRSOC 301 for design and 304 for welding. But EN 1090 appears in specifications for projects with European engineering, and it is mandatory for any structural component sold in the European Union: to export there, a shop has to have its factory production control certified under EN 1090-1 by a notified body, and only then can its components carry CE marking. It is worth understanding what it asks for even where local codes do not require it: specifications often use it as a reference for setting controls.
If you are asked for an EXC2 structure, you are being asked for a level of control, not a type of steel. The useful question is not “which steel?” but “who controls it, and how is it demonstrated?” If your specification includes an execution class, send it to us at Indumor and we will tell you what controls it implies and how we document them.
Send it to us and we will tell you what controls it implies and how we document them.
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