Press Information
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| Issued: August 2008 |
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Behind the Screens
Rainscreen specifications are largely driven by design appearance, as the systems offer an aesthetic finish and give architects the flexibility to be more creative with the exterior building envelope. However, the specification of a rainscreen reaches beyond surface aesthetics, with the choice of carrier system proving integral to the final finish achieved. William Harwood, T.I. Dynamic Facades, discusses the role that carrier systems have to play in rainscreen design, and shares advice on how to choose the best carrier for a specific requirement.
The primary function of a carrier rail is to create the minimum 30mm unrestricted zone for the rainscreen and hold the tiles/panels in place. There are two types of carrier system on the market – vertical and horizontal. While horizontal carriers have been in use for some time, vertical hangings are a more recent development and offer a number of on-site benefits.
Vertical versus horizontal
Compared with standard horizontal carriers, vertical systems significantly reduce the number of fixings required, and the fixings used are designed to be virtually invisible. As well as simplifying the installation, this preserves the aesthetics of the exterior finish.
Engineered with ease of use in mind, some vertical carriers actually make it impossible for a tile/panel to be fitted incorrectly. As well as offering peace of mind to the developer in terms of site safety, this also 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/panel replacement and removal. Individual tile/panel access also makes the installation of service lines at the end of a site programme straightforward, as the tiles/panels are easily removed and then replaced, until the most appropriate point of entry is identified.
Vertical: what’s available
Within the suite of vertical carriers available, there are a number of different system types, the selection of which will generally be determined by two main factors: budget and project requirements.
The most frequently specified vertical carrier is a belt and braces rail. This is because it can be fixed back to a horizontal or vertical subframe, offering flexibility in terms of total system approach. Moreover, it offers the most cost effective installation solution for standard module sizes of 400mm by 600mm.
Where there is a more complex rainscreen design, such as a mixture of tile/panel sizes, an adaptive rail should be used. An adaptive rail, as its name suggests, can easily accommodate the vertical joint variations associated with the use of different tile sizes. Higher performing adaptive rails typically achieve joints of 2mm to 40mm, which allows the rail to be adjusted to compensate for the difference in tile sizes. Even where the tiles/panels are homogenous or similar in size, an adaptive rail can be used to purposefully create joint variations, which may be specified by the architect as a design feature of the tiled/panel finish.
The third main type of vertical carrier is a clinch system. The clinch rail was originally designed for over-cladding existing facades. However, it is now commonly used with larger formats of tiles where a vertical subframe is the preferred option. This type of rail is the most cost effective option where cladding will be used as a façade only, making it ideal for use with composite panels and SIPs. In addition, the tight construction it delivers ensures a high quality exterior finish is achieved whilst maximising internal floor space for developments.
All of these systems can be used to create a facetted structure, although smaller module sizes are recommended. Where a tight facet must be achieved with larger tiles, or a horizontal subframe incorporates large spans, specification advice should be obtained from the façade manufacturer.
Down to detail
When choosing a rainscreen carrier system, cost of purchase and labour required for installation are primary considerations. These are then evaluated in the context of individual project demands such as design features and the specified subframe. However, a factor frequently overlooked is the detail of system installation. More specifically, the number of small moving parts, such as tile clips and fixings, which are required to keep tiles/panels in place.
Out of the systems identified as compatible, the one with the fewest moving parts or components should always be chosen. As well as simplifying and increasing the efficiency of installation, systems that do not have many moving parts are more cost effective. Cost savings are achieved because small tile clips are expensive to purchase and the loss rate of these on-site is extremely high – mainly due to boxes being opened, spilled and discarded.
Ultimately, to ensure the maximum design impact is achieved and the most cost effective carrier system is selected, it is important to carefully evaluate project requirements as early on in the specification process as possible. In doing so, the aesthetics of the building envelope will be preserved and at the same time a practical solution with regard to on-site installation is ensured.
