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BRE Crack Classifier

Free online BRE Digest 251 crack damage classifier with Eurocode 2 crack width check. Classifies damage category 0-5 with cause guidance.

Last updated 17 March 2026

About this tool

Classify building crack damage using the BRE Digest 251 system (categories 0–5) and check crack widths against Eurocode 2 (BS EN 1992-1-1) Table 7.1N limits.

Enter a measured crack width and the tool returns the damage category, pattern-specific guidance on likely causes, an EC2 compliance check, and a monitoring or repair recommendation.

Useful for building surveyors, structural engineers, and anyone carrying out condition surveys of masonry or concrete structures.

How to use this tool

Enter crack width — the measured width in mm (e.g. from a crack gauge or comparator card).
Select crack pattern — horizontal, vertical, diagonal/stepped, map/pattern, or random. This provides guidance on likely causes.
Select exposure class — for the EC2 crack width compliance check. XC1 allows 0.4 mm; all other classes allow 0.3 mm.
Review results — the tool shows the BRE damage category, pattern guidance, EC2 check, and a repair recommendation.

What is BRE Digest 251?

BRE Digest 251 (revised 1995) is a widely used UK classification system for assessing damage in low-rise buildings due to progressive foundation movement.

It categorises damage from 0 (negligible) to 5 (very severe) based primarily on crack width, with descriptions of typical visible damage and repair implications at each level. It is routinely referenced in structural surveys, subsidence claims, and insurance assessments.

Technical information

BRE Digest 251 categories

0 Negligible — < 0.1 mm
1 Very Slight — 0.1 to 1 mm
2 Slight — 1 to 5 mm
3 Moderate — 5 to 15 mm
4 Severe — 15 to 25 mm
5 Very Severe — > 25 mm

EC2 Table 7.1N crack width limits (base Eurocode recommended values, quasi-permanent load combination):

XC1: 0.4 mm
All other classes (XC2–XC4, XD1–XD3, XS1–XS3): 0.3 mm

Revision history

17 March 2026: Initial release

Disclaimer

This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.

Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.

All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.

By using this tool, you accept full responsibility for how you interpret and apply the information provided.

Spotted an error? Let us know.

Crack Width (mm)

Crack Pattern

Exposure Class (EC2 Check)