TECHNICAL BULLETIN
ISSUE 29
JULY 2018
ASSESSING THE SAFETY OF HIGH-RISE BUILDINGS A YEAR ON FROM GRENFELL TOWER: WHAT ISSUES ARE LIKELY TO BE OF CONCERN TO RESIDENTIAL PRACTITIONERS? PHIL PARNHAM MRICS
DIRECTOR, BLUEBOX PARTNERS
The fire at London’s Grenfell Tower on 14 June 2017 was a human tragedy. As the disaster continues to be covered by the media and numerous investigations roll on, this article will focus on issues likely to be of concern to residential practitioners. As ever, we try to provide suggestions on both evaluating the issues and reporting to clients. We have to stress these are no more than our own opinions and you must evaluate any suggestions given yourselves as practicing professionals.
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What type of cladding is causing the problem?
Understanding the cladding system is key to properly analysing situations such as Grenfell. Often called ‘rainscreen cladding’, this system has been around for more than 50 years, and over the last two decades has become the dominant cladding for most highrise buildings. Typically, most systems are non-load bearing. External cladding panels consist of several components: 1. An outer skin of rainscreen cladding panels fixed to a metal supporting frame. The frame is fixed back to the structure of the building. Its main function is to protect from rain and improve the cosmetic appearance of the building. The panels do not provide thermal insulation. 2. A ventilated cavity. As it is impossible to exclude all moisture (particularly wind-driven rain on upper
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floors), the system includes a ventilated and drained cavity to tackle small amounts of water that get past the rainscreen. Most cavities are at least 25mm wide. Thermal insulation. Usually fixed directly to the structure of the building. Depending on the manufacturer’s system, the outside surface of the insulation may be further protected using breathable sheathing felt. A wide range of materials are used including mineral insulation (such as Rockwool) or rigid foamed polymeric boards (such as Celotex). An airtight vapour control layer. Usually positioned on the warm side of the insulation (often on the surface of the existing wall), this has two primary functions. The first is to reduce the amount of water vapour getting into the wall construction from the inside of the building and the second to provide a layer to reduce air leakage into and out of the building. If this layer is not airtight, wind-driven rain will be able to penetrate the building itself due to differences in pressure.
This rainscreen cladding must be sealed to other parts of the building façade, such as other types of adjacent cladding, windows and doors. If these seals are ineffective, it may not meet water and fire resistance standards. Fire-stopping is particularly important because if flames reach into the ventilated cavity they could quickly spread around the outside of the building. Typical locations of
