BSBG has teamed up with Design Confidence to provide a series of fire safety master classes aimed at demystifying certain aspects of fire safety design. The series has a focus on the UAE, however, the principles largely apply internationally. This technical discussion, the second part of the series, is written by Hammad Rizvi to be used for the design process, and is related to exterior building façades in the UAE.
A façade is generally one exterior side of a building; usually, but not always, the front. Façade is a foreign loan word from the French, which means “frontage” or “face“. In architecture, the façade of a building is often the most important aspect from a design standpoint, as it sets the tone for the rest of the building. From an engineering perspective, the façade is also of great importance due to its impact on energy efficiency.
The intention of this article is to describe the minimum code requirements to ensure that flame spread on an exterior façade is restricted.
In the Middle East, building codes are largely influenced by the American Code, and standards such as the International Building Code (IBC) and the National Fire Protection Association standards. In Dubai the primary building code is the UAE Fire Code.
This building code privies the basis from which building façade systems are designed. This code provides detailed design guidelines for each façade system.
Cladding, other than thermal barriers and sandwich panels, is a non-structural covering installed over structural surfaces. It is usually made up from Metal Composite Materials (MCM), but is also available in a variety of other building materials and is made to tolerate extreme weather conditions.
Cladding options include:
Interior fires are intervened and controlled by automatic sprinkler systems or by firefighters. However, when the fire grows, reaching the ‘flash over’ stage, it leaps out from openings onto the exterior façade or cavities behind the façade of the building causing a “leap frog” effect.
If floor slab fire stopping is absent or fire stop material is not approved and not installed as per standards, or if the curtain-wall is not listed, the flames can penetrate through the gaps and reach for the upper floors. Flames can even propagate downwards if the material on the façade is flammable.
As the intense heat develops behind the façade and flames continue to grow, façade panels delaminate, exposing more core material to the flame, often resulting in a sudden engulfing of vast areas and multiple storeys of the building façade.
Apart from combustible façade materials, poor installation, poor joint detailing, poor mechanical detailing in fixing insulation and façade panels and poor railing system installations contribute to rapid façade flame spread and the collapse of façade panels and frames, making external fire fighting extremely difficult.
Thus the whole mechanism involved in façade flame spread, after initial ignition, can be pinpointed to the following factors:
Building Fire Rating
Façade materials, exterior wall systems, claddings and insulation installed on any building should not reduce the fire resistance rating of the exterior wall.
Cavity Fire Barrier
Cavity Fire Barriers shall be incorporated into façade design at every floor vertically to restrict flame spread laterally. The diagram below illustrates a cavity fire barrier installation.
Metal Composite Materials and Panels (MCM, ACP)
Exterior Insulation and Finish Systems (EIFS) and External Thermal Insulation Composite System (ETICS)
Perimeter Fire Barrier System (Curtain-wall)
On recent BSBG projects, the new UAE Fire Code has been specifically applied, given its mandatory nature within the UAE. Design Confidence continues to work closely with BSBS’s specialist façade design team to provide a balance between visual aesthetic and fire life safety requirements. This integrated approach ensures that the design maintains its signature look and feel while still achieving the fire safety objectives of the design and prescriptive requirements of the codes. This holistic, total approach is integral to the design process, as late changes can impose unnecessary cost and visual impact.
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