Overview
Damage to an adjoining owner's property during party wall works is uncommon, but it can happen. When it does, the scale of the damage matters.
A measured response depends on objective assessment, not alarm. Not every crack is structural, and not every defect is caused by the works.
Why cracks appear
Cracks can arise for many reasons, including:
- construction vibration or impact;
- ground movement or settlement;
- seasonal moisture and temperature changes;
- historic movement;
- ordinary shrinkage in finishes.
That is why photographs, dates and a proper schedule of condition are so useful.
The BRE crack classification
Surveyors and engineers commonly refer to the BRE Digest 251 classification when assessing cracking.
It provides a practical scale:
Negligible damage
Grade 0: hairline cracks below 0.1mm. No repair is usually required.
Grade 1: fine cracks up to 1mm. Redecoration is usually sufficient.
Slight to moderate damage
Grade 2: cracks up to 5mm. Filling and redecoration, or minor repointing externally, may be needed.
Grade 3: cracks between 5mm and 15mm. Localised masonry repair, repointing or some brick replacement may be required. Weather-tightness may be affected.
Severe damage
Grade 4: cracks between 15mm and 25mm. Structural repair is likely to be needed, and distortion may be visible.
Grade 5: cracks greater than 25mm. Major structural repair or rebuilding may be required.
What owners should do
If damage is alleged:
- measure the crack width;
- photograph it clearly;
- compare it with pre-works condition records;
- identify whether it is new or historic;
- seek professional advice for anything beyond minor cosmetic cracking.