Eurocode: what it governs, and what it changes on the drawing.

The Eurocode family, part by part

Eurocode is ten design standards published as one coordinated set, each covering a material or a hazard rather than a single document trying to cover everything.

• EN 1990, Basis of structural design — the common basis: limit states, load combinations and reliability that every other part builds on.
• EN 1991, Actions on structures — the loads: self-weight, imposed loads, wind, snow, thermal and accidental actions.
• EN 1992, Design of concrete structures — reinforced and prestressed concrete design.
• EN 1993, Design of steel structures — structural steel design, from member resistance to connections and plated structures.
• EN 1994, Design of composite steel and concrete structures — where steel and concrete act together, most commonly composite beams and slabs.
• EN 1998, Design of structures for earthquake resistance — seismic design, applied across the material parts above rather than replacing them.

The family also runs to EN 1995 for timber, EN 1996 for masonry, EN 1997 for geotechnical design and EN 1999 for aluminium structures, though steel, concrete and composite construction carry most of the detailing volume.

EN 1997 earns more attention than that list implies on anything with a difficult foundation. It sets the ground investigation a design has to rest on, the geotechnical categories that decide how much investigation is enough for the risk, and the design approach — selected by each National Annex — that fixes which partial factors are applied to actions, material properties and resistances when bearing capacity, sliding and overall stability are verified. Two countries applying different design approaches to the same ground do not arrive at the same footing.

A drawing rarely sits under one part alone. A composite frame in a seismic zone draws on EN 1992, EN 1993, EN 1994 and EN 1998 at once, each governing a different part of the same connection.

National Annexes: why Eurocode is not one code

The base Eurocode text leaves a defined set of values open — partial safety factors, load combination choices, seismic zonation, national choices on fire and durability provisions — and calls them nationally determined parameters. A partial factor for steel resistance, a snow load zone, or the fire resistance period required for a given occupancy are all typical examples — small numbers with a large effect on member size. Each country that adopts Eurocode publishes a National Annex that fixes those values for its own territory, and some annexes add non-contradictory complementary information on top.

That means EN 1993 alone is not a complete design basis. EN 1993 with the German National Annex and EN 1993 with the UK National Annex can produce different member sizes from the same geometry and the same load case. Naming the Eurocode without naming the National Annex is the single most common gap between a specification and a design that can actually be checked, and it is the first thing recorded at intake on any Eurocode package.

How Eurocode becomes mandatory, and which edition

The Eurocodes are European standards, not European law. Each country adopts them into its own building regulation, republishes them under its own national designation with the EN retained — BS EN, DIN EN, NF EN — and withdraws the national standards that conflict with them. That withdrawal is what makes the adoption real. Once a country's coexistence period ends, the superseded national code stops being a route to compliance for new design, and the Eurocode with the National Annex is the route.

The family is now being revised as a whole. New parts are published progressively, and each country has to issue a National Annex for each new part before that part can be used there, so for a period the same country can be designing to a new edition of one part and the previous edition of another. Naming the part, the edition and the annex together is the only unambiguous way to state a Eurocode design basis, and it is what a checking engineer or an approving authority will compare the calculation against.

A package therefore records three things at intake rather than one: the Eurocode part, its edition, and the National Annex of the country of construction.

EN 1090-2, EN 13670 and execution class

Design standards decide member sizes. Execution standards decide how the structure is actually made, and that is where Eurocode reaches the drawing. EN 1090-2 covers execution of steel structures — welding, bolting, fabrication and erection tolerances, and inspection — and EN 13670 does the equivalent for concrete: formwork, reinforcement placement tolerances, curing and inspection regimes.

EN 1090-2 assigns every steel structure an execution class from EXC1 to EXC4, set by consequence class and the production category of the structure. The execution class is not a formality: it decides which welds need non-destructive testing and how much, what welder qualifications are required, how tight the fabrication tolerances are, and what gets recorded and traced. Two structurally identical connections detailed under EXC2 and EXC3 carry a different amount of information on the sheet, because the standard requires it.

EN 1090-1, factory production control and market access

EN 1090-2 tells a fabricator how to make the steelwork. EN 1090-1 governs whether they may place it on the market at all. It sets the conformity assessment route for structural steel and aluminium components, and it requires the fabricating works to operate a factory production control system, assessed and certified by a notified body, before it can issue a declaration of performance for what it produces.

The two standards are joined at the execution class. The class assigned under EN 1090-2 determines the scope the works' certification has to cover, and a works certified only to a lower class cannot supply components for a structure specified at a higher one. Welding quality requirements follow the EN ISO 3834 series, whose parts run from comprehensive quality requirements down to elementary, and the execution class again decides which part applies and what welding coordination the works has to have in place.

None of this is paperwork that arrives after fabrication. It decides which works can legally make the structure — a question worth settling before a connection is detailed to a class the intended works is not certified for, and before an execution class is raised late in design without anyone checking who can still build it.

What Eurocode changes in a detailing package

A package produced under Eurocode carries the National Annex and the execution class on its face, not as background information. Reinforcement detailing follows the anchorage, lap length and minimum bend diameter rules in EN 1992-1-1, adjusted by whichever National Annex governs. Steel connections follow EN 1993-1-8, the joints part, for bolt spacing, edge distances and weld design resistance. Drawings issued for fabrication state the execution class so the fabricator applies the right tolerance and inspection regime without having to ask.

None of this is optional detail. A steel connection designed to EN 1993-1-8 and drawn without its execution class stated is a drawing a fabricator cannot legally execute to EN 1090-2, because the class is what tells them how to make it.

How we check a package against Eurocode

The automated checks on a Eurocode package are configured to the specific National Annex agreed at intake, not to a generic version of the standard. Bolt edge distances and hole clearances are checked against EN 1993-1-8, minimum bend diameters and anchorage lengths against EN 1992-1-1, and every drawing is checked for a stated execution class that matches what EN 1090-2 requires for the structure's consequence class.

Where a programme spans more than one country, each package is checked against its own National Annex rather than one being quietly reused for all of them. A senior engineer reviews the checked package and signs it before it is issued, and the check record travels with the drawing so the National Annex it was verified against is never in question later.