All buildings must be designed and built to ensure that the exterior envelope is weathertight. For walls, this means considering the components as a system to manage water – cladding, flashings, air barriers and so on.
Designers must select exterior claddings that are appropriate to the building design and location and must provide sufficient detail to allow the builder to accurately assemble the cladding components.
Cladding details must reflect the specific building requirements – generic cladding details may not be sufficient with complex, higher-risk buildings in higher-risk locations. Designers and builders must also consider how the cladding assembly will perform under extreme conditions, such as heavy consistent wind-driven rain or where there may be a fault in the cladding, when it is possible that water will penetrate the cladding and enter the assembly, by incorporating drainage and drying so that the water is dealt with.
Designers can select from a wide range of exterior wall cladding systems, some of which perform better than others with respect to weathertightness.
Designers need to specify cladding materials not just on an aesthetic basis, but because they are appropriate. Considerations include:
- specific environmental conditions of the site
- building design
- surface finish requirements
- availability of appropriately skilled and experienced installers
- compatibility with other cladding systems on the building
- maintenance requirements.
The size and style of the building influences cladding selection. A building that has higher weathertightness risks (see risk evaluation) should use cladding systems that offset those risks. If a building has risk features such as no eaves, a complex building envelope with many junctions and being multi-storey, specifying a difficult cladding system or multiple cladding systems will further increase weathertightness risks.
Some claddings rely upon a surface finish to remain weathertight and for durability. The performance of the surface finish is fundamental to the cladding performance.
Builders should ensure that they can source suitable quality tradespeople to install and finish the cladding system. Some claddings require specialist installers, and these may not be available in some locations.
Many building designs have more than one exterior cladding. Designers must be sure that the cladding systems can work together and that suitable weathertight details can be incorporated, particularly at the junction between dissimilar claddings. Builders should raise any concerns they have about cladding details with the designer.
Most claddings require regular maintenance, and some building designs can make this difficult to achieve. The ability to access the cladding for maintenance, repair or replacement must be a consideration.
Updated: 5 April 2019