The short answer
Damage from party wall works is uncommon, but when alleged it should be assessed proportionately, not with alarm. The BRE crack classification gives an objective framework, and the existence of a crack does not prove the works caused it.
Why it matters
Cracks can be caused by construction vibration or impact, settlement or ground movement, seasonal expansion and contraction, historic movement, or shrinkage in plaster and finishes. The BRE scale, widely used by surveyors and engineers, grades severity:
- Grade 0 (negligible) — hairline cracks below 0.1mm; usually no repair.
- Grade 1 (very slight) — fine cracks up to 1mm; redecoration usually enough.
- Grade 2 (slight) — cracks up to 5mm; filling, redecoration and minor external repointing may be appropriate.
- Grade 3 (moderate) — cracks 5mm to 15mm; localised masonry repair, repointing or brick replacement may be needed, and weather-tightness may be affected.
- Grade 4 (severe) — cracks 15mm to 25mm; structural repair may be required, with distortion to doors, windows, floors or walls.
- Grade 5 (very severe) — cracks over 25mm; major structural repair or rebuilding may be required.
What to do now
- Inspect before reacting and measure the crack width.
- Compare against the schedule of condition.
- Consider whether the crack is new, historic or progressive.
- Seek engineering advice where the crack is significant.
Common mistakes
- Assuming any crack proves the works caused it.
- Overreacting to minor cosmetic cracking, or ignoring genuine damage.
- Assessing damage with no schedule of condition to compare against.
When to call Coburns
If damage is alleged and you need a proportionate, evidence-based assessment, get in touch and we will measure it against the proper framework.