A year after polystyrene insulation, diagonal cracks appeared at window corners. Thermography and probes revealed insufficient anchoring and missing dilatation joints.
A year after the external thermal insulation system (ETICS) was installed on an apartment building in Prague 6, significant diagonal cracks began to appear at window reveals. The owner asked me to assess the cause and propose a remedy.
Diagnostics
- Insufficient anchoring — fewer fasteners per m² than required by the manufacturer’s specification
- Missing dilatation joints in long façade sections
- Thermal bridges at window reveals due to under-detailed reinforcement
Conclusion
Cracks were caused by the combination of insufficient anchoring and thermal stress. I recommended additional anchoring with screw fasteners into the load-bearing structure, dilatation profiles, and reinforcement repair. The investor implemented the repair the following season.