Execution classes EXC1 to EXC4 under EN 1090
An execution class (EXC) is the level of requirements for making a steel or aluminium structure under EN 1090. There are four classes: EXC1 is the lightest and EXC4 the most demanding. The higher the class, the stricter the requirements for welding, inspection and recording.
The class is not a choice you make for your certificate. The designer sets it per project in the specification documents. Your EN 1090 certificate states which class you may work to. For welding, the class determines which part of ISO 3834 you need. Background on the legal side is available from Bouwen met Staal (Dutch steel construction information platform) .
Short answer: EXC1 for simple structures with small consequences of failure, EXC2 for most buildings, EXC3 for structures with large consequences of failure or fatigue loading, and EXC4 for special structures with extreme consequences.
Overview of the execution classes with examples
The table below gives a typical example for each class. The examples are indicative. The designer sets the class based on the design, the loading and the national annex of the Eurocode.
| Class | Typical application | Example |
|---|---|---|
| EXC1 | Simple structures, small consequences of failure, static loading | Agricultural barn where few people come, simple greenhouse |
| EXC2 | Most buildings with a normal consequence class | Industrial hall, office building, residential building, steel landing |
| EXC3 | Large consequences of failure or fatigue loading | Grandstand, large canopy with many visitors, many bridges |
| EXC4 | Special structures with extreme consequences | Only per project specification, with extra requirements per weld |
In practice, most Dutch steel fabricators work to EXC2. If you make bridges or heavily loaded structures, you often need EXC3. EXC4 is rare and always requires additional agreements in the project.
Who sets the execution class under EN 1090?
The designer, not the steel fabricator. Since EN 1090-2:2018, the rules for the choice are in the Eurocode for steel structures, NEN-EN 1993-1-1, annex C. The old rule of thumb “if no class is stated, then EXC2” no longer exists in the 2018 edition. The class must therefore always be stated explicitly in the execution specification.
The choice starts from the consequence class in the Eurocode NEN-EN 1990. This describes how serious it is if the structure fails:
| Consequence class | Meaning | Usual execution class under static loading |
|---|---|---|
| CC1 | Small consequences for people, the economy or the environment | EXC1 |
| CC2 | Medium consequences | EXC2 |
| CC3 | Large consequences | EXC3 |
With fatigue or earthquake loading, the class can be one step higher. National annexes may deviate from this. Use this table as a guide to reading, not as a replacement for the calculation.
Example: one project, two classes
A steel fabricator delivers a hall with a crane runway. The designer chooses EXC2 for the rafters and purlins. For the crane runway girders, which are subject to changing loads, the designer chooses EXC3. The drawings state the class for each component.
The workshop must then be certified for both classes. A certificate up to and including EXC2 is not enough here. Always check on your certificate which class it applies to.
How the execution class appears in the specification documents
A clear execution specification prevents discussion later. The fictional example below shows the data you as a steel fabricator want to see for each component.
| Component | Execution class | Steel grade | Protection | Remarks |
|---|---|---|---|---|
| Rafters, grid lines A to F | EXC2 | S355J2 | Hot-dip galvanised | None |
| Crane runway girders | EXC3 | S355J2 | Blast-cleaned and coated | Subject to fatigue loading, additional investigation |
| Landing and staircase | EXC2 | S235JR | Hot-dip galvanised | None |
If a column is missing, such as the execution class, ask the designer for it before you confirm the order.
What changes per execution class in the workshop?
The class mainly determines the requirements for welding. The table below is a simplified overview based on EN 1090-2. Always check the details against the standard itself.
| Subject | EXC1 | EXC2 | EXC3 | EXC4 |
|---|---|---|---|---|
| ISO 3834 part | Part 4 (elementary) | Part 3 (standard) | Part 2 (comprehensive) | Part 2 (comprehensive) |
| Welding coordinator (ISO 14731) | Not required | Required, usually basic (B) or specific (S) | Required, specific (S) or comprehensive (C) | Required, comprehensive (C) |
| Weld acceptance level (ISO 5817) | Mostly level D | Mostly level C | Level B | Level B plus extra requirements per weld |
| Additional non-destructive testing | Scope according to table in EN 1090-2 | Wider than EXC1 | Wider than EXC2 | Recorded per project |
The knowledge levels B, S and C correspond to the well-known welding qualifications: B corresponds to International Welding Specialist (IWS), S to International Welding Technologist (IWT) and C to International Welding Engineer (IWE). The knowledge level of the welding coordinator depends on the class as well as on the steel grade and the plate thickness. EN 1090-2 has a separate table for this. More on welding coordination is on the ISO 3834 page.
What does the auditor want to see for the execution class?
During the initial inspection, the notified body checks whether your working method suits the class you apply for. In practice, an auditor often asks for:
- A recent project file in which the execution class appears on the drawing or in the specification.
- Welding procedure specifications (WPS) and qualifications that cover that class.
- An appointed welding coordinator with a suitable knowledge level and a clear description of their tasks.
- Weld inspection reports, with the correct acceptance level.
- How you check an order when the class is missing from the documents.
That last point matters. A good contract review catches a missing class before production starts.
Common mistakes with execution classes
Choosing a class yourself. The steel fabricator may not fill in the class if the designer forgets it. Ask the designer in writing and record the answer.
Certifying too high. A certificate for EXC3 sounds good, but it requires a more senior welding coordinator and more testing. Choose the class that your work actually requires.
Certifying too low. The reverse causes problems with a crane runway or a bridge section. Look ahead to the contracts you want to take on in the coming years.
Accepting one class for the whole project. Components can have different classes. Read the drawings for each component.
Frequently asked questions about execution classes
May I make EXC2 work with an EXC3 certificate?
In practice, a certificate for a higher class also covers the lower classes. You then apply the requirements of the lower class, unless the project asks for more. To be sure, check your certificate and confirm with your notified body.
Does the execution class also apply to aluminium?
Yes. EN 1090-3 for aluminium structures uses the same four classes. The technical requirements do differ from steel, for example for welding and surface preparation. To see how this works in practice, read EN 1090-3 for aluminium.
Can I apply for a higher execution class later?
Yes. You apply to your notified body for an extension of the certificate. You then show that you meet the stricter requirements, for example with a welding coordinator at a higher level and additional welding procedure qualifications. The notified body usually assesses the extension during an additional or regular visit.
What if the designer does not state a class?
Then stop and ask the designer. Under EN 1090-2:2018, there is no longer an automatic default class. Record the request and the answer in your project file, as part of your ISO 9001 document control or your FPC records.