"If a roof structure is not properly triangulated, roof spread can occur. The roof can push the walls out of vertical at the top. The walls may also bow. It is often related to poor design or alterations, such as re-roofing with a heavier material than the original roof covering. Tie bars are often used to restrain walls. Movement can be progressive and serious."
"KEY FEATURES:
1. Poorly triangulated roofs.
2. Heavy roof coverings.
3. Walls pushed out of vertical.
4. Tapering cracks usually wider at top.
5. Displacement is greatest at the mid span of the purlins.
6. Displacement increases between restraining walls."
Source: Holland, M. (2012). A practical guide to diagnosing structural movement in buildings. Chichester, West Sussex [England]: Wiley-Blackwell.
Cracks that accomplish this tesis:
>At the second floor
Crack codes:
CSB20
CSC22
CSB23
CSB25
CSB27
CSB33
CSB40
CSB40
CSB64
Forces diagram:
–Principle
–Second floor
