Fire Safety Masterclass | Chapter Two - Exterior Building Façades

Words by BSBG Media Team, Monday 22 January 2018

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.

Exterior façades

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.

Code Basis

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.

Types of exterior façade systems

Cladding

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:

Metal Composite Material (MCM), (including Aluminium Composite Panels (ACP))
Exterior Insulation and Finish System (EIFS)
External Thermal Insulation Composite Systems (ETICS)
Perimeter Barrier
Curtain-wall

Flame spread on exterior façades

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:

Readily combustible core of the façade material (Insulation/Sealants/Panels)
Inferior façade panel integrity (poor panel make and skin bonding)
Non-tested and non-listed façade, sealants and fire stopping systems
Poor installation of façade and fire stopping systems
Lack of thermal barriers and cavity fire barriers

Code Requirements

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)

MCM/ACP Core should not be made of foam plastic insulation, LDPE (Low Density Polyethylene) or any such expanded plastic (with a density less than 320 kg/m³).
MCM/ACP Core should be tested and evaluated separately. Core (exposed without skin) used in cladding and façade panels can be made of plastic or minerals, or a combination of both, with flame and smoke spread characteristics as per TEST 1 in accordance with Table 1.14.a. and Table 1.14.b. test requirements.
MCM/ACP panels and façade systems on non-fire resistance rated and non-load-bearing exterior wall coverings should comply with Table 1.

MCM/ACP panels and facade systems on fire resistance rated exterior and non-load bearing wall assembly coverings should comply with Table 2.

Exterior Insulation and Finish Systems (EIFS) and External Thermal Insulation Composite System (ETICS)

EIFS and ETICS should be constructed so as to meet the performance characteristics required as per ASTM E 2568.
The layers and core materials should be tested separately before entire assembly; including ornaments, trims and moldings with prescribed thickness, joints, seams, fasteners and wall arrangement.
EIFS must be specified in accordance with ANSI/EIMA 99-A (Latest Edition) ‘American National Standard for EIFS’. ETICS meets the performance requirements as per ETAG 004 (Latest Edition) ‘Guidelines for European Technical Approval of ETICS with Rendering’.
EIFS and ETICS panels and facade systems on non-fire resistance rated and non load bearing exterior wall coverings should comply with Table 3.
Requirements of the ANSI/EIMA 99-A or ETAG 004 guidelines should be followed independently. Using parts from each of the guidelines is not permitted.

Perimeter Fire Barrier System (Curtain-wall)

The perimeter barrier should be intended to restrict the interior vertical passage of flame and hot gases from one floor to another at the location where the floor intersects the inside of an exterior curtain wall. The perimeter fire barrier shall remain securely in place and provide interior joint protection for the time period no less than the fire-resistance rating of the floor assembly.
Openings in exterior walls in adjacent stories should be separated vertically at least 36 in. (915 mm) by spandrel panels with a fire-resistance rating of at least one hour or a flame barrier extending horizontally at least 30 in. (760 mm) beyond the exterior wall with a one-hour fire-resistance rating.
The components of the curtain wall and fire stopping should be such that if sections of the curtain wall are damaged or collapse, the integrity of firestop and its ability to provide the required fire resistance is not compromised.
All perimeter barrier systems should be listed and approved system assemblies.
Vertical separation between spaces leased to different tenants and between public and nonpublic spaces should be protected to achieve a fire-resistance rating equal to that of the vertical wall assembly.
Where ventilation and air gaps are required behind the façade, such as with rain screens or as part of the design, the vertical open gap between the exterior façade and building envelope should have approved cavity barriers using intumescent fire stopping arrangements at every floor joint.

Design Confidence and BSBG

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.

To find out more about Design Confidence, you can visit their website: www.designconfidence.com or follow them on LinkedIn here.

BSBG Media Team

Related Articles

Technical Note | Drywalling Part 1

Technical Note | Waterproofing external areas

An introduction to external cladding