What are the BRE crack damage categories?

BRE Digest 251 defines six categories of damage in low-rise masonry buildings: 0 Negligible (hairline, <0.1 mm), 1 Very slight (up to ~1 mm), 2 Slight (up to ~5 mm), 3 Moderate (5–15 mm), 4 Severe (15–25 mm) and 5 Very severe (over ~25 mm). Categories 0–1 are aesthetic, 2–3 affect serviceability, and 4–5 affect stability.

Does crack width alone tell you the category?

No. BRE Digest 251 classifies damage by ease of repair, and gives crack width only as a guide. The number of cracks, their position (especially over openings), and their effect on doors, windows and structure can all raise the category. This tool uses width as the starting point and lets you flag the corroborating factors.

Does this tool diagnose subsidence?

No. It classifies the severity of visible damage to BRE Digest 251. It does not diagnose the cause, nor whether movement is active or progressive. Diagnosis requires monitoring over time (ideally through the seasons) and, for Category 3 and above with progressive signs, assessment by a chartered structural engineer.

How should I measure a crack width?

Measure at the widest point of the crack using a crack-width gauge or feeler. Record the length, location, orientation and whether it passes through bricks or follows the mortar joints, with dated photographs. For monitoring, fit a calibrated tell-tale (e.g. an Avongard gauge) and re-read it periodically.

When should a structural engineer be involved?

As a guide: Category 3 cracking that is tapering, progressive or affecting weather-tightness, and all Category 4–5 cracking, should be referred to a chartered structural engineer. Category 5 may require the building to be made safe. Where ground movement is suspected, this may also engage the building insurer under a subsidence claim.

Is this suitable for a RICS Home Survey or condition report?

It is an independent screening and classification aid that helps you record cracking consistently to BRE Digest 251 within a RICS Home Survey Standard report or condition report. It is not a substitute for the surveyor's professional judgement, a specialist structural assessment or the official Digest.

Where can I get the official BRE Digest 251 publication?

Obtain a licensed copy of BRE Digest 251 from BRE Group’s official publications shop or an authorised supplier. This independent calculator is a field aid that uses paraphrased category guidance; it is not the Digest and does not reproduce the publication.

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BRE 251 Crack Classification Assessment Guide

An independent field aid for recording cracking in masonry buildings against BRE Digest 251. Enter the crack width and observations to get a category (0–5), damage class and report-ready next step; it does not diagnose the cause of movement.

BRE Digest 251RICS condition reportsSubsidence triageFree to use

Crack measurements

Widest crack width3.0 mm

015 mm30 mm+

Exact value (mm):

Measure at the widest point of the crack with a crack-width gauge.

Corroborating signs (BRE 251 classifies by ease of repair — these can raise the category)

Crack pattern (for possible causes)

BRE Digest 251Serviceability

Slight

Typical width: up to about 5 mm

Cracks easily filled; recurrent cracks can be masked by suitable linings. Cracks may be visible externally and some repointing may be required. Doors and windows may stick slightly.

Typical repair

Fill internally; repoint affected external brickwork.

Recommended action

If cracks are tapering, diagonal or appear to be recent, fit crack monitors (tell-tales) and re-measure over 6–12 months before concluding.

Possible causes to investigate

Record the pattern, length and location with dated photos so the cause can be assessed on monitoring.

This tool classifies severity — it does not diagnose the cause. Confirm by monitoring and, where needed, a structural engineer.

Prepared by (optional)

Property / reference (optional)

BRE Digest 251 — categories of damage

Cat.	Degree	Approx. width	Class
0	Negligible	less than 0.1 mm	Aesthetic
1	Very slight	up to about 1 mm	Aesthetic
2	Slight	up to about 5 mm	Serviceability
3	Moderate	5 to 15 mm (or several cracks over 3 mm)	Serviceability
4	Severe	15 to 25 mm (also depends on number of cracks)	Stability
5	Very severe	usually over 25 mm (also depends on number of cracks)	Stability

Width bands are a guide. BRE Digest 251 classifies damage by ease of repair; several cracks, position over openings and structural effects can place damage in a higher category than width alone suggests.

About BRE Digest 251 and this field aid

BRE Digest 251 is a copyrighted professional publication. For the full method and its original context, obtain a licensed copy from BRE Group’s official publications shop or an authorised supplier.

This independent calculator is not the Digest and does not reproduce it. It uses paraphrased category guidance to help record observations consistently on site; the surveyor’s judgement, the official publication and specialist advice remain decisive.

Using this correctly

Frequently Asked Questions

Disclaimer: This tool classifies the severity of visible cracking to BRE Digest 251 using the widest crack width and your observations. Width is indicative; the Digest classifies by ease of repair. It does not diagnose the cause of cracking, nor whether movement is active or progressive, and is not a substitute for inspection by a chartered surveyor or a structural engineer. Always record cracking with dated photographs and measurements, and recommend specialist assessment where the category or pattern warrants it.

Record cracking properly, on-site.

PropertySurvey Pro lets you photograph, annotate and classify defects against RICS Home Survey and condition-report standards, then generate a branded PDF before you leave the property.

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