EN 1090

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EN 1090 Execution Classes: Complete Guide to EXC1, EXC2, EXC3 & EXC4

By PZVAR Technical Editorial Team

13 Min Read

12 Aug 2026

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Introduction

EN 1090 Execution Classes define the level of execution, quality control, inspection and fabrication requirements applicable to structural steel and aluminium components. The four classes are EXC1, EXC2, EXC3 and EXC4, with the level of requirements generally increasing from EXC1 to EXC4.

Choosing the correct execution class is important because it affects welding requirements, inspection, traceability, quality documentation, personnel competence, fabrication controls and the overall EN 1090 compliance process.

However, an important point is often misunderstood:

The execution class should not be selected simply because a structure is a “building,” “bridge,” or “industrial structure.”

The applicable execution class is determined through the design and project requirements, taking into account factors such as consequence class and the relevant service and production characteristics. EN 1090-2 and EN 1090-3 link execution requirements to the structural design framework.

What Is an EN 1090 Execution Class?

An Execution Class (EXC) specifies the level of execution requirements that apply to a structural component or structure.

EN 1090 provides four classes:

Execution Class	General Level
EXC1	Basic execution requirements
EXC2	Standard execution requirements
EXC3	Higher execution and quality requirements
EXC4	Highest/special execution requirements

The progression is important:

EXC1 → EXC2 → EXC3 → EXC4

As the execution class increases, the required level of control and verification generally becomes more demanding.

EN 1090-3, for example, explicitly states that four execution classes are provided and that the required strictness increases from EXC1 to EXC4.

Why Are Execution Classes Important?

Execution classes provide a structured way to match fabrication and execution controls with the structural consequences of failure.

The execution class can influence:

Welding quality requirements
Welding coordination
WPS and WPQR controls
Welder qualifications
Inspection requirements
NDT
Material traceability
Quality documentation
Production controls
Personnel competence
Manufacturing records
FPC implementation

This means that selecting the wrong EXC can create significant compliance problems.

For example, a manufacturer may have an excellent welding system but still fail to meet the project’s requirements if the required execution class was incorrectly identified or the applicable inspection level was not followed.

What Are EXC1, EXC2, EXC3 and EXC4?

EXC1 – Basic Execution Class

EXC1 represents the lowest of the four execution classes.

It is intended for structures or structural components where the consequences associated with execution failure are comparatively lower and the applicable design/project rules permit EXC1.

Typical examples can include relatively simple structural components, but the actual classification must be determined from the project/design requirements rather than from the component name alone.

Typical characteristics

EXC1 generally has:

Lower execution complexity
Less demanding documentation
Lower levels of inspection than higher EXCs
Less stringent traceability requirements
Basic welding quality requirements where welding is involved

For aluminium structures, EN 1090-3 provides execution-class-dependent requirements and specifies different levels of quality documentation, inspection documentation and traceability between EXC1 and the higher classes.

Important

EXC1 does not mean “no quality control.”

The manufacturer still needs to comply with the applicable technical requirements and execution specification.

EXC2 – Standard Execution Class

EXC2 is a commonly encountered execution class for structural fabrication.

It represents a higher level of execution control than EXC1 and introduces additional requirements for areas such as documentation, welding, inspection and production control.

For many manufacturers, EXC2 becomes particularly important because it requires a more structured production and welding-quality system.

Depending on the applicable standard and project, requirements can include:

More extensive quality documentation
Controlled welding procedures
Qualified welding personnel
Welding coordination
Increased inspection
Better material identification
Production records
Defined inspection and testing plans

For aluminium structures, EN 1090-3 identifies EXC2 as requiring inspection certificates 3.1 for constituent products and additional marking requirements when different alloys or tempers are in circulation.

EXC3 – Higher Execution Requirements

EXC3 introduces significantly more demanding execution and quality controls.

It is used where the structural consequences and/or project requirements justify a higher level of fabrication control.

Compared with EXC2, manufacturers should expect stronger requirements relating to:

Welding quality
Traceability
Inspection
Documentation
Production control
Welding coordination
Personnel competence
Quality assurance

For aluminium fabrication, EN 1090-3 requires constituent products in EXC3 and EXC4 to have inspection certificate 3.1 and requires traceability through the stages of execution.

Welding requirements

The welding quality level becomes particularly important at higher execution classes.

EN 1090-3 associates:

EXC1 → EN ISO 3834-4
EXC2 → EN ISO 3834-3
EXC3/EXC4 → EN ISO 3834-2

for the specified welding-quality requirements.

The exact requirements should always be checked against the applicable edition of the execution standard and the project specification.

EXC4 – Highest Execution Class

EXC4 is the highest execution class in the EN 1090 framework.

It represents the most demanding level of execution control and is associated with structures or components where particularly high consequences or special requirements apply.

EXC4 should not simply be interpreted as “EXC3 with more paperwork.”

It can involve substantially more stringent requirements concerning:

Manufacturing
Welding
Inspection
Traceability
Quality documentation
Personnel competence
Verification
Special project requirements

The actual requirements depend on the applicable execution standard, design basis and execution specification.

Requirement	EXC1	EXC2	EXC3	EXC4
Execution strictness	Basic	Standard	High	Highest
Quality documentation	Lower	Increased	Extensive	Extensive
Material control	Required	More controlled	Higher traceability	Highest control
Traceability	Limited depending on requirement	Increased	Strong	Strong
Welding control	Basic applicable requirements	Controlled	More demanding	Most demanding
Welding quality level*	ISO 3834-4	ISO 3834-3	ISO 3834-2	ISO 3834-2
Inspection	Basic applicable level	Increased	Higher	Highest/special
Production control	Required	Required	More stringent	Most stringent
Typical risk level	Lower	Normal/standard	Higher	Exceptional/special

*The welding-quality relationship shown above is based on the EN 1090-3 execution-class provisions for aluminium and should not be blindly applied to every project without checking the applicable edition and material-specific execution standard.

How Is the EN 1090 Execution Class Selected?

This is one of the most important parts of EN 1090.

The execution class should come from the design and execution specification, rather than being chosen independently by the fabricator simply because one class appears easier or more economical.

The selection involves the structural design framework.

A simplified process is:

Determine the structural consequences

↓

Determine the applicable consequence class

↓

Consider service category

↓

Consider production category

↓

Determine the applicable execution class

↓

Include the EXC in the execution specification

↓

Manufacturer implements the corresponding fabrication controls

EN 1090-3 specifically states that execution classes are linked with consequence classes and notes that recommendations for selecting execution class in relation to consequence class are given in EN 1999-1-1 for aluminium structures.

Who Determines the Execution Class?

The execution class is fundamentally a design/project decision, not simply a certification body’s choice and not something the fabricator should select based only on convenience.

The relevant project documentation should establish the required execution class.

The manufacturer then needs to ensure that its production and FPC arrangements are capable of meeting that class.

In practice:

Designer/Engineer/Project Specification

→ defines applicable requirements

Manufacturer/Fabricator

→ implements them

Certification/Notified Body

→ assesses the manufacturer’s conformity within its applicable certification scope

If the execution class is unclear, the manufacturer should obtain clarification before production begins.

Can One Structure Have More Than One Execution Class?

Yes.

This is an important point.

Execution classes do not necessarily have to be identical throughout an entire structure.

EN 1090-3 states that execution classes may apply to:

The whole structure
A part of the structure
Specific details

and that a single structure may contain several execution classes.

For example, a project might specify:

Main structural members → EXC3
Secondary members → EXC2
Particular critical details → EXC4

The actual arrangement must come from the project/design requirements.

What Happens If No Execution Class Is Specified?

This is another area where manufacturers should be careful.

For the aluminium execution standard cited above, EN 1090-3 states that if no execution class is specified, EXC2 applies.

However, manufacturers should not assume that every situation can simply be treated as EXC2.

The applicable standard edition, design basis, national provisions and project specification must be checked.

If the project documentation does not clearly identify the execution class, obtaining clarification from the responsible designer/project authority is the safer approach.

How Does Execution Class Affect Welding?

Execution class has a direct impact on welding requirements.

For a manufacturer, the welding system should cover areas such as:

Welding procedures
WPS
WPQR
Welder qualification
Welding coordination
Welding consumables
Welding parameters
Preheating
Interpass temperature
Welding inspection
NDT
Welding records

Higher execution classes generally require more rigorous control.

For aluminium structures, EN 1090-3 specifies different ISO 3834 quality levels according to execution class.

This is why manufacturers should establish their execution-class scope before finalizing their welding documentation.

Execution Classes and Material Traceability

Material traceability also becomes increasingly important at higher execution classes.

For aluminium structures, EN 1090-3 specifies that for EXC3 and EXC4, constituent products are to be traceable at all stages of execution between delivery and incorporation into the structure.

A practical traceability chain can look like:

Material Certificate

↓

Heat/Batch Identification

↓

Cutting

↓

Part Identification

↓

Fabrication

↓

Welding

↓

Inspection

↓

Finished Component

This allows the manufacturer to establish what material was used in a particular component.

Execution Classes and Inspection

As the execution class increases, inspection and quality-control requirements can become more demanding.

Depending on the structure and applicable requirements, inspection can include:

Dimensional inspection
Visual weld inspection
Surface inspection
NDT
Verification of material
Production inspection
Final inspection

The required inspection extent should not be guessed from the EXC alone.

The manufacturer should examine:

EN 1090-2 or EN 1090-3
Design documentation
Execution specification
Drawing requirements
Applicable inspection requirements
Project-specific specifications

Execution Class and EN 1090 Certification

Manufacturers seeking EN 1090 certification need to establish a scope that reflects the products and execution classes they intend to manufacture.

For example, a manufacturer may have certification covering:

Structural steel components – EXC1 and EXC2

Another manufacturer may need:

Structural steel components – EXC1, EXC2 and EXC3

The certification scope should correspond to the manufacturer’s actual capabilities and the requirements applicable to its products.

A company should not advertise or claim an EXC level that it is not certified or otherwise qualified to manufacture within its applicable conformity-assessment scope.

Common Mistakes When Selecting an Execution Class

Mistake 1: Choosing EXC2 Automatically

Some manufacturers assume:

“Most companies use EXC2, so we’ll use EXC2.”

This is not a sound method.

The execution class needs to be established from the applicable design/project requirements.

Mistake 2: Selecting EXC Based Only on Building Type

Saying:

“It’s a warehouse, therefore EXC2.”

is not sufficient.

Two structures with similar purposes can have different structural consequences and therefore different execution requirements.

Mistake 3: Assuming Higher EXC Is Always Better

Choosing EXC4 for everything may sound safer, but it can introduce unnecessary manufacturing, documentation and inspection requirements.

The correct approach is to use the execution class required by the applicable design/project basis.

Mistake 4: Ignoring Project Specifications

A project specification can contain additional requirements beyond the baseline standard.

The manufacturer should review the complete execution specification before production.

Mistake 5: Applying Steel Rules to Aluminium

EN 1090-2 applies to steel structures, while EN 1090-3 applies to aluminium structures.

Although both use EXC1–EXC4, their detailed technical requirements are not identical.

EN 1090-3:2019 specifically covers aluminium structural components including rolled products, extrusions, cold-drawn products, forgings and castings.

EN 1090 Execution Class Audit Checklist

Before accepting a project, a manufacturer can ask:

Project Requirements

Is the applicable execution class clearly specified?
Is the execution specification available?
Has the design documentation been reviewed?
Are project-specific requirements identified?

Materials

Are required material grades known?
Are material certificates available?
Is traceability appropriate for the EXC?
Are material identification procedures established?

Welding

Are applicable WPS available?
Are WPS qualifications appropriate?
Are welders/operators qualified?
Is welding coordination appropriately assigned?
Are welding consumables controlled?
Are inspection requirements understood?

Production

Are current drawings available?
Are production procedures controlled?
Are manufacturing personnel competent?
Are inspection records maintained?

Quality

Is the required inspection level defined?
Are NDT requirements understood?
Are non-conformities controlled?
Is required documentation retained?

Certification

Does the manufacturer’s EN 1090 certification scope cover the required EXC?
Does the FPC system support the applicable execution class?
Are the manufacturer’s production capabilities adequate?

Frequently Asked Questions

What are the four EN 1090 Execution Classes?

The four execution classes are:

EXC1, EXC2, EXC3 and EXC4.

The required strictness generally increases from EXC1 to EXC4.

Which is the highest EN 1090 Execution Class?

EXC4 is the highest execution class.

Is EXC2 the standard execution class?

EXC2 is commonly encountered, but it should not automatically be selected for every project. The applicable execution class must be established according to the relevant design and project requirements.

Who decides the EN 1090 Execution Class?

The execution class is established through the applicable design/project requirements and execution specification. The manufacturer implements the requirements in production.

Can one structure have multiple execution classes?

Yes. Execution classes can apply to the whole structure, a part of the structure or specific details.

Does EXC3 require more inspection than EXC2?

Generally, higher execution classes bring more stringent execution and inspection requirements, but the exact inspection extent must be determined from the applicable EN 1090 part, project specification and design requirements.

Does execution class affect welding?

Yes. Execution class affects welding-quality requirements and associated controls. For aluminium structures, EN 1090-3 specifies different ISO 3834 quality levels for different execution classes.

Is EXC4 required for every bridge?

No. The execution class should not be assigned solely from the structure’s name. It must be established using the applicable design and execution requirements.

Conclusion

EN 1090 Execution Classes provide a framework for controlling the level of fabrication and execution required for structural components.

The four classes are:

EXC1 → EXC2 → EXC3 → EXC4

with increasing levels of execution strictness.

For manufacturers, understanding the execution class is essential because it can influence:

Welding
WPS/WPQR
Welder qualifications
Welding coordination
Material traceability
Inspection
NDT
Production controls
Documentation
FPC requirements
EN 1090 certification scope

The most important rule is simple:

Do not choose the execution class based on guesswork, structure type or convenience. Establish it from the applicable design, project and execution requirements before production begins.

For steel structures, manufacturers should refer to the applicable requirements of EN 1090-2; for aluminium structures, EN 1090-3 is the relevant execution standard. EN 1090-3:2019 is currently listed as an active edition by national standards bodies including NEN and NBN.

If your company is preparing for EN 1090 certification or an execution-class audit, PZVAR can help assess your FPC, welding documentation, production controls and certification requirements against the applicable execution class.