What crack width is considered structural?
There is no single legal number. BCA's standard PSI report template gives minor reinforced concrete cracks under 2 mm wide and under 30 mm deep as an example of a minor structural defect, and structural cracks as structural defects. The UK BRE Digest 251 scheme for low-rise masonry treats cracks up to about 5 mm as aesthetic, 5 to 25 mm as serviceability issues and wider cracks as stability issues. Width is only one factor; location, pattern and movement matter as much.
From the RRD Field Guide, checked against the sources cited in Cracks in Walls, Beams and Ceilings in Singapore: Which Are Structural and When to Worry. General information, not advice for your project.
The fuller picture
Most hairline cracks in plaster, paint and at wall-to-beam joints are non-structural, caused by shrinkage and thermal movement. Worry when cracks are wide or widening, diagonal or stepped, tapered, recurring, accompanied by rust stains, sagging or sticking doors, or appear in beams, columns or slabs. Monitor with dated tell-tales and call a Professional Engineer for those signs.
More questions on this topic
- Are hairline cracks in walls normal?
- Which cracks should I worry about?
- How do I monitor a crack?
- Who repairs cracks in a condominium?
- Can I fill cracks myself before selling or renting out?
- Do cracks in a new home fall under the developer's defects liability?
- Does the Periodic Structural Inspection look at cracks?