02.03 Curtain Walls
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Introduction
Rainscreens are often thought of as a form of overcladding to masonry walls however all walls with a ventilated cavity are considered as rainscreens. Rainscreens can be created using various forms of curtain walling as follows:
- Dry lining system
The rainscreen panels may be supported on frames or cladding rails fixed to the building at intermittent points, often to the edges of the floor slabs, and a dry lining applied to the back of the frames. This type of rainscreen can be referred to as ‘built-up’ and is shown in this image.
- Prefabricated support wall
Many systems which appear to be panellised or unitised curtain walling systems (factory built) are actually rainscreen systems in which the rainscreen panels hang onto the outer face of the prefabricated element as shown in this image.
- Stick system backing wall
In this type of wall, which might be termed an ‘integral’ construction, the insulation is in the form of prefabricated panels held in a stick system curtain walling frame, with the rainscreen panels fixed to the outside of the stick system, either directly onto the face of the insulated panels or onto a secondary supporting framework fixed to the stick system. This is illustrated in this image.
Loads
All the above systems utilize some form of frame which supports both the backing wall and the rainscreen panels. Both the rainscreen panels and the backing wall must be designed to carry the appropriate wind load, Section 02.06, however, as the wind load is only applied to the structure once, the wind load carried by the frame will be the total wind load not the sum of the loads on the rainscreen and inner lining.
The fixings attaching the frame to the structure must carry both the full wind load and the dead load of the rainscreen and inner wall. The dead weight may be substantial if the backing wall is a precast concrete panel or if stone rainscreen panels have been used. There may also be significant moments induced by the offset of the line of action of the dead load from the point of support.