As water drains down wall surfaces or across roofs and decks, it passes over joints, junctions and intersections that need to be watertight. Wall claddings are also vulnerable where there are penetrations such as windows, doors, meter boxes and pipes.

To be able to assess, design and construct exterior cladding details, designers and builders need to understand:

• how water behaves on the exterior of a building
• how water will behave once it has leaked into exterior assemblies 
• what types of buildings and building details have a higher risk of water penetration.

Roof and wall penetrations require careful design and detailing.