Rainscreen façade cladding
Find out more about rainscreen cladding options available through PMJ Masonry.
Rainscreen cladding originally evolved through research in the early 1960’s in Norway and Canada, both addressing issues associated with leakage and moisture penetration, where single barrier protection failed under prevailing weather conditions.
Originally based on the use of timber to form a secondary ventilated protective screen, this design principle has been adopted worldwide as a means of protecting a building through the extremes of inclement weather, be it precipitation or temperature fluctuations. There are now multiple materials being used as the screen, including various types and thicknesses of natural stone.
A natural stone clad rainscreen system is a form of façade system, which consists of a sub frame, panelised cassette or rail-based system that is clad with natural stone panels. The rainscreen cladding system gives the appearance of a solid walled structure without having to use mortar joints to bind the sections of stone together.
Pending design, this allows for ventilation through air circulation through natural ventilation or when the backing framework is compartmented, leading to a pressure equalised cavity complete with drainage, to channel away any water ingress.
This maintains a dry cavity therefore maximising weather protection to the weather sealed inner façade, ensuring additional protection against water ingress and enhanced long-term insulation performance.
The principal British standard for stone clad rainscreen systems is BS 8298-04 :2020, Design and installation of natural stone cladding and lining, Part 4: Stone cladding on rainscreen support systems – Code of practice.
Correctly specified, a rainscreen cladding system will provide weathering and insulating properties through controlling water, wind movement and penetration. In addition, when the system is designed in coordination with an appropriately detailed and specified fire barrier compartmentation scheme, this will provide the appropriate level of protection against the spread of fire and smoke within the cavity void.
There are two design approaches to rainscreen cladding systems, including:
- Drained and ventilated rainscreen
- Pressure-equalised rainscreen
Both can be used for new build and refurbishment work to existing envelopes.
A cladding support framework is used in the system. This can be made from aluminium as opposed to more expensive stainless-steel components. The overall sub fame assembly would be dependent on the cavity width to accommodate insulation and the size and weight of the individual panels of stone.
The frame is placed within the cavity between the weathered backing structure, external cladding and secured in line with the bespoke design solution. The natural stone panels are then secured to the support frame using additional fixings.
Again, the type of fixing adopted will be dependent on the size and weight of individual panels. These could include rail systems secured within a kerf slot or using a factory installed undercut anchor onto which patch rails are secured with the panel. This is in turn fixed to a receiving rail tied to the primary structure or secondary frame arrangement.
Rainscreen cladding is also an alternative to storey to storey closed cavity cladding. The benefits come when the design is contemporary “flat plate” design. The introduction of projections to throw off water and create shadow and relief, can complicate the design when assessed in comparison to normal storey to storey cladding. However, combining the two approaches, if considered early enough in the design process, can provide the best of both worlds.
It is encouraged that early dialogue is taken when considering this solution, which is something that the PMJ team are more than happy to support.