October 2008
Designer Façades
Rainscreen cladding is favoured as a modern method of construction primarily because of the speed with which it can be installed. However, advances in rainscreen cladding technology have given rise to a new generation of exterior façades, which are as popular for their stylish finish as they are for practicality. William Harwood, director, T.I. Dynamic Facades, discusses the developments behind these latest façade innovations, and explains why, through intelligent engineering, they are affordable for a wide range of developments.
While the primary function of a rainscreen is to protect the inner leaf of a building from wind driven rain and ultra violet light, modern rainscreen design allows the use of a wide range of aesthetic materials. Early patterns suggest that natural products, such as stone and terracotta, are emerging as the most preferred. Although historically the preserve of premium developments, advances in product manufacture and carrier system technology have helped bring the cost of these natural finishes down, making them more affordable than ever before.
Manufacturing innovations
The two main natural materials used for rainscreen cladding are stone and terracotta. Where terracotta is concerned, the main technological advancement has been the development of a viable single skin system.
In the past, terracotta tiles have had to incorporate a twin skin design to deliver the required impact performance. Through innovative manufacturing techniques, a lighter weight single skin tile can now be used, which is easier to manage on-site because it simplifies the installation process. This single skin terracotta rainscreen delivers impact performance and durability equal to that of twin skin by using a porcelain base in the raw material with a high baking temperature.
Developing a lighter weight system was also a high priority with the stone façades because these traditionally had to be very thick – approximately 40mm – to deliver the required load bearing performance. This made stone expensive to purchase and costly to install.
Façade manufacturers have overcome this challenge by creating a facing that is reinforced with a high strength fibre, aluminium or aluminium honeycomb backing. Stone facings are manufactured 6mm to 15mm thick and bonded to one of the backing systems, with the type of backing determined by the specification requirements of a project.
Sandstone, limestone, granite, basalt, slate and marble can all be manufactured in this way to achieve a durable, high performance finish, without the need for a stonemason. While this offers an on-site cost saving because it substantially reduces site programmes, it also brings the overall system cost down because less of the raw material is required per square metre.
Developments behind the rainscreen
To achieve even greater cost savings, innovations have also been pioneered behind the rainscreen, with the development of precision calculated carrier systems for both stone and terracotta.
One of the main shifts in carrier system technology is the development of vertical hangings. Compared with standard horizontal subframes, vertical systems significantly reduce the number of fixings required, and the fixings used are designed to be virtually invisible. As well as reducing the complexity of the installation, this preserves the aesthetics of the exterior envelope.
Engineered with ease of use in mind, some vertical carriers make it impossible for a tile to be fitted incorrectly. This contributes to increasing the speed of installation, because it is much simpler to find the correct place for the tile.
Once installed, a vertical carrier gives greater flexibility in terms of tile replacement and removal. Individual tile access makes the installation of service lines at the end of a site programme straightforward, as the tiles are easily removed and then replaced, until the most appropriate point of entry is identified.
The development of innovative natural rainscreen finishes means that this high quality façade is no longer only the preserve of premium developments. As they continue to deliver on aesthetics as well as affordability, these natural façades are expected to rise in popularity at all levels, from specification through to construction.