Overview
Damage arising from party wall works is uncommon, but when it is alleged, proportional assessment is essential.
Overreaction creates unnecessary disputes. Underreaction can leave genuine damage unresolved. The BRE crack classification provides a useful objective framework.
Common causes of cracking
Cracks may be caused by:
- construction vibration or impact;
- settlement or ground movement;
- seasonal expansion and contraction;
- historic movement;
- shrinkage in plaster or finishes.
The existence of a crack does not prove that party wall works caused it.
The BRE damage scale
The BRE classification is commonly used by surveyors and engineers to describe crack severity.
Grade 0 - negligible
Hairline cracks below 0.1mm. Usually no repair is required.
Grade 1 - very slight
Fine cracks up to 1mm. Redecoration is usually enough.
Grade 2 - slight
Cracks up to 5mm. Filling, redecoration and minor external repointing may be appropriate.
Grade 3 - moderate
Cracks between 5mm and 15mm. Localised masonry repair, repointing or brick replacement may be needed. Weather-tightness may be affected.
Grade 4 - severe
Cracks between 15mm and 25mm. Structural repair may be required. Doors, windows, floors or walls may show distortion.
Grade 5 - very severe
Cracks greater than 25mm. Major structural repair or rebuilding may be required.
Practical steps
When damage is alleged:
- inspect before reacting;
- measure crack width;
- compare with the schedule of condition;
- consider whether the crack is new, historic or progressive;
- seek engineering advice where the crack is significant.