STRUCTURAL ELEMENTS 89 SUPPORTING ROLE


ENABLING THE MASONRY SUPPORT SYSTEM, CAVITY BARRIER AND CAVITY TRAY TO ALL BE ACCOMMODATED AT THE EDGE OF A FLOOR SLAB NEEDS VERY CAREFUL COMPONENT SELECTION


Masonry is an increasingly popular cladding choice for high rise buildings. However, the selection and co-ordination of the masonry support system and cavity fi re barriers is critical for the facade to perform eff ectively in a fi re, as Ben Williams of SIG explains.


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rick and stone have been the cladding materials of choice for architects and builders for centuries due to their strength, durability and ease of maintenance, combined with a natural timeless aesthetic. Masonry is a particularly popular cladding choice for high rise residential buildings with a concrete supporting structure. A masonry facade on a high rise building typically comprises two layers: an outer masonry skin and an inner leaf separated by a cavity. The outer skin can be stone or brickwork, or even a brick slip mounted on a backing board, to form a weather-protective rainscreen. The inner leaf can be formed from a variety of materials, including blockwork or


most commonly an internal framed and sheathed structure incorporating thermal insulation.


A masonry support system is used to transfer the load from the external brick, block or stone skin back to the main supporting structure. This support generally comprises a system of stainless- steel brackets attached to the supporting structure. The brackets span the facade cavity to support a horizontal ledge which, in turn, supports the weight of the outer masonry leaf. It is important that any horizontal movement joints are located to the underside of the masonry support system to enable differential movement between the facade and the structure to be accommodated.


Along with the masonry support system bracets, the edge of each fl oor slab also must accommodate a horizontal cavity barrier. Cavity barriers are essential in helping to subdivide the cavity formed between the outer masonry wall and its inner leaf into smaller compartments to prevent fi re spreading vertically in the (chimney-like) void.


In addition cavity trays are also needed within the cavity to prevent the water that passes through the outer leaf reaching the interior of the building. They must be formed from non-combustible materials for buildings over 11 metres, and they must be installed where the downward fl ow of moisture is interrupted by an obstruction, such as a horizontal cavity


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