---
title: BS EN 1090 & Execution Classes (EXC1–EXC4) Explained
url: https://www.koyda.com/guides/bs-en-1090-execution-classes/
description: What BS EN 1090-1, -2 and -3 cover, how execution classes EXC1 to EXC4 are chosen, why EXC2 is the UK default, and CE versus UKCA marking for steelwork.
last_modified: 2026-10-10
publisher: Koyda Ltd, Units 27–29 Jesmor Farm, St Piers Lane, Lingfield, Surrey RH7 6PN. 07753 213617, joe@koyda.com
---

Technical guide

# BS EN 1090 and Execution Classes, Explained

BS EN 1090 is the standard for fabricating structural steel and aluminium. Part 1 covers certification and marking, and Part 2 covers how steelwork is made. The execution class (EXC1 to EXC4) sets how strict the fabrication controls are.

Last reviewed 10 October 2026 · Koyda Ltd

## Key points

* BS EN 1090-1 covers factory production control (FPC), certified by a notified or approved body. That certification is needed to CE or UKCA mark structural components.
* BS EN 1090-2 covers the technical requirements for steel; BS EN 1090-3 covers aluminium.
* If the designer does not specify an execution class, EXC2 applies (BS EN 1090-2, clause 4.1.2). Most UK building steelwork is EXC2.
* CE marking is recognised in Great Britain indefinitely, and UKCA marking remains valid.

## The three parts

| Part | What it covers |
| --- | --- |
| BS EN 1090-1 | How conformity is assessed: factory production control, initial type testing, and declarations of performance for CE or UKCA marking |
| BS EN 1090-2 | Technical requirements for steel structures: materials, cutting, welding, bolting, tolerances, inspection |
| BS EN 1090-3 | Technical requirements for aluminium structures |

## Execution classes

There are four execution classes, from EXC1 (least strict) to EXC4 (most strict). The designer chooses the class. Annex B of BS EN 1090-2 gives guidance using the consequence class of the structure, the service category (static or fatigue loading) and the production category.

* **EXC1:** simple structures with low consequences of failure, such as some agricultural buildings
* **EXC2:** the default where no class is given, and the norm for UK buildings
* **EXC3 and EXC4:** structures with high consequences of failure or significant fatigue loading, such as large stadiums and bridges

In the UK, the BCSA's National Structural Steelwork Specification (NSSS, 7th edition) is based on EXC2. It requires a welding quality system to BS EN ISO 3834-3 for EXC2.

## Welding requirements behind the class

* Welding quality management to BS EN ISO 3834 (the part depends on the class)
* Welding procedures qualified to BS EN ISO 15614-1
* Welders qualified to BS EN ISO 9606-1
* A responsible welding coordinator (BS EN ISO 14731)

## CE and UKCA marking

The government confirmed in September 2024 that CE marking is recognised for construction products in Great Britain indefinitely. The Construction Products (Amendment) Regulations 2025 came into force on 8 January 2026. UKCA marking with a UK approved body remains valid, and the government has said any future change will have at least two years' transition.

## What to ask a steelwork supplier

* The FPC certificate: execution class, certifying body and expiry date
* A declaration of performance for marked components
* Welding procedure qualifications and welder certificates
* The inspection and testing plan, and the traceability level

## Sources

1. [Construction products regulation in Great Britain (GOV.UK)](https://www.gov.uk/guidance/construction-products-regulation-in-great-britain)
2. [BCSA National Structural Steelwork Specification (NSSS)](https://bcsa.org.uk/resources/fabrication-technical-design/nsss/)
3. BS EN 1090-1, -2, -3 (BSI)

General guidance only, not design advice for a specific project. Check the current edition of each document.

ContentsGuide

1. [The three parts](#parts)
2. [Execution classes](#exc)
3. [Welding requirements behind the class](#welding)
4. [CE and UKCA marking](#marking)
5. [What to ask a steelwork supplier](#ask)

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