Curtain walling

When a component or system fails, it ceases to perform in accordance with the design intent. The failure mode is the way in which that failure occurs. Research suggests that water penetration is the most frequent failure mode, with buildability and durability being additional concerns (Layzall, J., Failure mode and effects analysis in the cladding industry, University of Bath, 1997).

The underlying factors that influence water penetration failures are generally due to a lack of knowledge of cladding installers, fabrication errors and contractual pressures such as late running on site.

Defective pressure plate system to a glazed rooflight. The clamping of the outer gaskets is insufficient and water penetrates the outer gasket into the drainage channel. Water in the drainage channel cannot escape owing to the lip of the roof upstand obstructing the channel at the bottom of the photograph. Note silicone top capping to try and alleviate leakage on the right of the photo.

A study by Day in 1993 identified the different causes of failure; some 35 of his sample reflected failings in workmanship, while 22% were failures in design (Day, R., What effect will the publication of the new Standard and Guide to Good Practice have on Curtain Walling failures in the UK?, 1993).

In 1997, a CWCT study (Cladding Component Failures) concluded that there were 5 main causes of watertightness failure :

• defective sealant joints;
• incorrect selection and sealing of corner joints in gaskets;
• mitre joints in windows;
• poorly sealed frame connections; and
• missing or sealed drainage holes and redundant fixing holes.

The same study identified sealants, gaskets and metal finishes as the components of cladding that were most likely to fail - often as a result of inappropriate or misguided selection and use.

Causes of curtain wall failures

Elements likely to cause problems