The Centre for Window and Cladding Technology (CWCT) is a publisher of industry standards and guidance on building envelopes. The CWCT ‘Standard for systemised building envelopes’ gives a framework for specifying building envelopes incorporating various performance criteria.
In conjunction with a certified testing facility, façade systems can be rigorously tested to ensure they comply with the relevant CWCT specification. Whilst façade performance can be calculated to a certain extent, it is no substitute for an actual physical test, replicating the most extreme conditions that buildings can be subjected to. PSP’s tested rainscreen façade systems have been proven to comply with the CWCT requirements under the following criteria:
- Air Permeability
- Wind Resistance
Both the National Building Specification (NBS) and National House Building Council (NHBC) standards are based on the CWCT ‘Standard for systemised building envelopes’.
A rainscreen façade is defined as a layered cladding system comprising of:
- A visible outer skin (rainscreen) that forms the primary rain barrier. This layer sheds the majority of water down its surfaces, but does not prevent the passage of air into the air gap.
- An air gap that prevents water ingress into the building. This provides ventilation and drainage, and can also be used to provide pressure equalisation across the façade.
- A backing wall that forms an effective air barrier and often includes an insulating layer. The carrier system or sub-frame for the outer skin is usually fixed to the backing wall.
PSP’s standard rainscreen systems are classed as ‘drained and ventilated’. This means that perimeter details are designed to allow ventilation and drainage to the cavity in line with standard rainscreen principles. The airflow through the cavity assists in removing water from the cavity, which then drains out at the base.
Rainscreen façade systems provide an aesthetically pleasing external envelope solution, whilst also offering rapid installation times. The construction methods used often mean buildings are weather tight at an earlier stage, thus allowing internal trades to commence earlier and subsequently shortening the overall construction programme.