Standards and compliance
Standards and compliance
BS EN 1090 execution classes: EXC2 and EXC3 explained
When a structural engineer specifies steelwork, they also assign an execution class to those components. That class tells the fabricator how stringent the manufacturing controls, quality documentation, and inspection requirements must be. For most buildings in the UK, the class is EXC2. More demanding structures require EXC3. Understanding the difference matters when appointing a fabricator, reviewing a tender, or checking what a specification requires of the contractor.
What BS EN 1090 sets out
BS EN 1090 is the British and European standard for the execution of steel structures. Part 1 covers conformity assessment and CE/UKCA marking. Part 2 contains the technical fabrication rules, including the execution class framework that determines the level of control required across the production process.
There are four execution classes: EXC1 to EXC4. Requirements become progressively more stringent at each level. EXC1 applies to structures with low consequences of failure, such as agricultural buildings. EXC2 covers most buildings. EXC3 applies to bridges and structures with higher consequences of failure or fatigue loading. EXC4 adds project-specific requirements on top of EXC3 and is reserved for safety-critical structures with extreme consequences of failure. For the vast majority of commercial and residential steelwork, EXC2 and EXC3 are the relevant classes.
How the execution class is determined
The designer specifies the execution class. It is not the fabricator’s decision and it is not a commercial choice: it follows a structured assessment using informative guidance in Annex B of BS EN 1090-2. If the contract documents do not state a class, BS EN 1090-2 assigns EXC2 by default. New Steel Construction’s published guidance confirms that EXC2 will cover the vast majority of buildings constructed in the UK.
The assessment uses three inputs:
- Consequence class: The severity of failure consequences for that structure, following the approach in BS EN 1990. A structure such as an agricultural building with low occupancy sits in a lower consequence class. A structure where failure would affect a large number of people sits in a higher one.
- Production category: PC1 covers non-welded components and those in steel grades below S355. PC2 covers welded components in higher-grade steel, site-welded connections, hot-formed sections, and certain hollow-section lattice components.
- Service category: SC1 covers predominantly static loading. SC2 covers structures subject to fatigue loading or located in areas of medium or high seismic activity.
Working through this matrix gives the execution class for the structure or for individual components. Different parts of the same structure can be assigned different execution classes. The class appears in the engineer’s specification documents and must be passed to the fabricator at enquiry stage.
What EXC2 requires of a fabricator
EXC2 is not a low-quality standard. A fabricator working to EXC2 must operate a certified Factory Production Control (FPC) system, independently assessed by an approved certification body. The FPC system covers material procurement and traceability, welding processes, dimensional inspection, surface treatment, and documentation throughout the production process.
From EXC2 upwards, a named Responsible Welding Coordinator must oversee all welding activities. Welding quality management must meet the relevant part of BS EN ISO 3834, as confirmed by Wright Engineering’s published technical guidance. Material traceability, weld procedures, and inspection records must be maintained for the duration of the project and retained afterwards.
To issue UKCA-marked structural steelwork, the fabricator must hold an assessed FPC certificate under BS EN 1090-1 and issue a UK Declaration of Performance for each batch of components at delivery. This is a legal requirement for structural steelwork placed on the GB market.
What EXC3 adds
EXC3 is typically required for bridges and structures with fatigue loading or a higher consequence of failure. New Steel Construction’s guidance cites pedestrian, bicycle, road, and railway bridges as typical EXC3 applications.
The requirements at EXC3 build on EXC2. The fabricator’s welding quality management system must meet BS EN ISO 3834-2, the more demanding of the two welding quality parts applicable to normal fabrication. Weld inspection and non-destructive testing requirements are more extensive. Documentation requirements across the whole production process are heavier. There is no separate list of EXC3-specific items; the requirements run throughout Part 2 and are flagged individually for each class.
A fabricator certified to EXC3 can carry out work at EXC1, EXC2, and EXC3. As New Steel Construction’s guidance sets out, a steelwork contractor with EXC3 capability can be used for EXC1, 2, and 3 work, while one certified only to EXC2 cannot take on EXC3 projects. Two Js Metalwork holds BS EN 1090 EXC3 certification.
UKCA marking and factory production control
In Great Britain, structural steelwork placed on the market requires UKCA marking. This replaced CE marking as the required conformity mark at the end of 2021. A fabricator holding UKCA marking confirms that its Factory Production Control system has been assessed by an approved certification body and is operational. When components are delivered, the fabricator issues a UK Declaration of Performance.
The FPC system is structured similarly to ISO 9001 but includes the additional welding quality management requirements specific to BS EN 1090. It covers the full production cycle from material purchasing through to final dimensional and surface inspection before despatch. Certification bodies such as BSI, TWI Certification, and ISOQAR assess and certify FPC systems to the relevant execution class. The certificate names the fabricator, the standard and edition, and the execution class scope.
A fabricator without a current, assessed FPC certificate cannot legally place UKCA-marked steelwork on the GB market.
Questions to ask your fabricator
| Question | Why it matters |
|---|---|
| Which execution class are you certified to? | Must match or exceed the class specified by the structural engineer |
| Which body assessed your FPC system, and when was the last assessment? | Confirms the assessment was independent and that certification is current |
| Do you hold current UKCA marking? | Legal requirement for structural steelwork placed on the GB market |
| Who is your Responsible Welding Coordinator? | Required for EXC2 and above; must be named and documented |
| Can you supply a UK Declaration of Performance at delivery? | Required for every batch of UKCA-marked structural components |
| Which edition of BS EN 1090-2 does your certificate reference? | Different editions are in use; confirm it matches the contract specification |
The execution class for your project should appear in the structural engineer’s specification. If it is not stated, ask the engineer to confirm it before the work goes to tender. A fabricator awarded work without a stated class must apply EXC2 as the default, which may not suit the project.
To discuss certification or a specific project specification, contact Two Js Metalwork at twojsmetalwork.co.uk/contact-metal-fabricators.
Written by Two Js Metalwork
Structural steel fabrication and architectural metalwork in Sussex. See the projects behind the advice.
