A Complete Guide to EN 1090 (EXC1, EXC2, EXC3, EXC4) for Structural Steel
If you’re in the process of planning a construction or engineering project involving structural steel, you’ve likely encountered a blizzard of technical terms: EN 1090, CE Marking, FPC, and, of course, EXC1, EXC2, EXC3, or EXC4.
To a project manager or developer, this can seem like confusing jargon. But these terms are the most important part of your project’s safety, legality, and quality.
These “EXC” ratings are Execution Classes, and they are the backbone of structural steel regulation in Europe. They are not suggestions; they are a legal requirement.
As an EN 1090-1 certified fabricator, the team at SIA Kurz deals with these standards every day. We believe it’s crucial for our clients to understand what they mean. This guide will talk about Execution Classes, explain how they are determined, and show why choosing the right fabrication partner is critical for your project’s success.
First, What is the EN 1090 Standard?
Before we can understand the classes, we have to understand the rulebook.
EN 1090 is a harmonized European standard that governs the fabrication and assembly of steel and aluminum structures. It is part of the Construction Products Regulation (CPR), which mandates that all fabricated structural components sold in the EU must have a CE Mark.
This CE Mark is your proof that the component meets the required technical and safety standards.
The EN 1090 standard is split into parts, but the two most important for fabrication are:
- EN 1090-1: This covers the requirements for conformity assessment (i.e., the rules for CE Marking). It requires the fabricator to have a certified Factory Production Control (FPC) system.
- EN 1090-2: This details the technical requirements for the execution (fabrication) of steel structures.
A central part of EN 1090-2 is the concept of Execution Classes.
How is an Execution Class (EXC) Determined?
An Execution Class is not chosen by the fabricator (like SIA Kurz) or the client. It is a design-stage decision made by the project’s structural engineer or designer.
The class is determined by assessing the risk involved. The question would be – “What would happen if this component or structure failed?”
To determine this, they analyze three factors:
- Consequence Class (CC): This assesses the potential consequences of failure in terms of human life, economic loss, and social impact.
- CC1: Low consequence (e.g., an isolated agricultural shed).
- CC2: Medium consequence (e.g., a standard residential or office building).
- CC3: High consequence (e.g., a stadium, a concert hall, a major bridge).
- Service Category (SC): This relates to the types of loads the structure will experience.
- SC1: Structures with primarily static loads (e.g., a standard building).
- SC2: Structures subject to dynamic loads, vibrations, or fatigue (e.g., bridges, crane girders, structures with heavy machinery).
- Production Category (PC): This relates to the complexity of the fabrication process, including the type of steel used and the welding involved.
- PC1: Non-welded components or components made from lower-grade steel.
- PC2: Welded components, components made from high-strength steel, or complex fabrication (like hot forming).
The engineer uses a matrix combining these three factors (CC, SC, and PC) to arrive at the required Execution Class. In short:
Higher Risk = Stricter Class
The 4 Execution Classes: A Detailed Breakdown
Here is what each class means in practice, from the least (EXC1) to the most (EXC4). The requirements for each class are cumulative, for example EXC3 must meet all EXC2 requirements, plus more.
EXC1: Low Risk
- Risk Level: Low
- Typical Applications: This class is for structures where the risk to human life and the consequences of failure are minimal.
- Examples: Agricultural buildings (barns, greenhouses), simple stairs and handrails in non-public areas, small sheds.
- Quality Requirements: Corresponds to EN ISO 3834-4 (Elementary quality requirements). Basic quality controls are needed, but requirements for welder qualification and traceability are minimal.
EXC2: The Standard
- Risk Level: Medium
- Typical Applications: This is the most common class and is the default for most standard building projects.
- Examples: Residential and commercial buildings, office blocks, warehouses, apartment buildings, and most structures not open to high-density public crowds.
- Quality Requirements: Corresponds to EN ISO 3834-3 (Standard quality requirements). This is a major step up. It requires a certified Factory Production Control (FPC) system, qualified welders, and formal Welding Procedure Specifications (WPS). Full traceability of materials and consumables is mandatory.
EXC3: High Risk
- Risk Level: High
- Typical Applications: This is for structures with a high risk to the public or those subject to dynamic loads where failure would be serious.
- Examples: Public buildings (stadiums, shopping centers, concert halls, hospitals), road and rail bridges, crane girders, and grandstands.
- Quality Requirements: Corresponds to EN ISO 3834-2 (Comprehensive quality requirements). This class demands everything from EXC2, plus much stricter process controls, higher levels of welder qualification, and significantly more inspection and Non-Destructive Testing (NDT) on welds.
EXC4: Extreme Risk
- Risk Level: Extreme / Catastrophic
- Typical Applications: This is the highest and most stringent class, reserved for “special structures” where failure is simply not an option.
- Examples: Critical components of nuclear power plants, major long-span bridges over populated areas, and structures in high-seismic zones with extreme design loads.
- Quality Requirements: Also corresponds to EN ISO 3834-2 (Comprehensive), but with the most rigorous application of all controls. It requires exhaustive documentation, 100% inspection (often with advanced NDT), and total traceability for every single part of the process.
What Your Execution Class Means for Your Project
Understanding the EXC for your project is vital because it directly impacts three key areas:
- Safety & Legality: This is the most important. Fabricating a component to a lower class than specified (e.g., using an EXC2-certified fabricator for an EXC3 bridge) is illegal and dangerous.. It invalidates the CE Mark and exposes you to massive liability.
- Cost & Schedule: A higher Execution Class requires more process control, more documentation, more inspection, and more testing. This adds administrative and testing overhead, which increases the cost and can extend the timeline. It’s crucial to budget for the correct class from the start.
- Your Choice of Fabricator: This is the critical link. A fabricator must be independently audited and certified for the specific Execution Class they are fabricating. A company certified only for EXC1 cannot legally produce EXC2 components.
This is why you must ask your fabrication partner: “What Execution Class are you certified for?“
The SIA Kurz Advantage: Your Certified EN 1090 Partner
At SIA Kurz, we have invested heavily in our quality systems to ensure full compliance. We are EN 1090-1 certified to deliver your project safely and legally.
When you partner with SIA Kurz, you aren’t just buying steel components; you’re buying the documented proof that your components are safe, compliant, and built to the exact standards your design demands.
