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Combustible materials: RIBA’s position explained

RIBA’s position on combustible materials following the Grenfell Tower disaster explained

04 September 2018

Following the devastating fire at Grenfell Tower on 14 June 2017, the RIBA argued for a ban on combustible materials in the external walls of high rise buildings. After a detailed investigation we believe this is the only way to ensure buildings were safe for the public.

In responding to the Ministry of Housing and Local Government’s (MHCLG) consultation on banning combustible materials, the RIBA took the opportunity to produce a robust set of recommendations for the UK Government and the industry.

These recommendations include:

  • A ban on combustible materials in external wall construction on buildings over 18m in height must be imposed.
  • Within external wall construction, the ban should restrict sheathing boards, insulation and outermost cladding products to European classification A1 products only. The ban should not include the buildings primary structure. The primary structure should have adequate fire protection (see Building Regulations Requirement B3).
  • The ban should restrict window spandrels, balconies, brise soleil, and similar building elements to European classification A1 products only.
  • The ban should restrict plasterboard to European Classification A2-s1, d0 products and above only, as the RIBA is unaware of any A1 certified plasterboard products.

How did we reach this position?

The RIBA carried out a detailed investigation on the products used in external wall construction. Advice was taken from specialists in designing, specifying and constructing cladding systems, insulation products, glazing, curtain walling, structural systems and external (protruding) systems.

The RIBA Expert Advisory Group on Fire Safety decided that RIBA should focus on:

  • Insulation
  • Outermost cladding products
  • Sheathing boards and plasterboard in external walls
  • Large systems that protrude from the buildings walls such as balconies and briese soleil

To provide a clear position for Government to act upon, the RIBA Expert Advisory Group agreed that primary structural elements should not be included in a ban as the MHCLG consultation clearly related to Building Regulations requirement B4 – external fire spread, rather than requirement B3 - internal fire spread (structure).

What is the difference between A1 and A2 classifications?

The standard ‘Fire classification of construction products and building elements’ sets the specific test methods and performance that products must be certified as meeting.

An A2 certified product has a higher combustibility and can sustain flame for no more than 20 seconds. In contrast, A1 has a lower combustibility and no sustained flaming when tested. Crucially, a product can be certified as A2 even if it gives off an unlimited amount of smoke and unlimited flaming particles/droplets.

In addition, it is necessary to understand that smoke is the most common cause of deaths in fires in the UK and that flaming particles/droplets will tend to initiate new fires away from the original point of ignition. For these reasons, the RIBA recommends that the proposed ban restricts the listed products to A1 only. Should the ban permit the use of A2 products, then these must be certified as meeting the classification A2 s1, d0 (limited smoke production and no flaming particles/droplets).

What will happen next?

The RIBA expects that a ban is likely and that it is applied through a change in the Building Regulation requirements. There are some suggestions that the ban may be applied before the end of 2018.

Our recommendations for members

Members are recommended to:

  • Follow the RIBA position on combustible materials in their designs
  • Carefully consider the performance characteristics of the key products that will go into external walls and on the outside of their buildings
  • Be sure they understand the classifications and how they relate to fire safety

We are aware that insurance brokers are requesting additional information relating to cladding and while it might be possible to negotiate cladding cover in some exceptional circumstances, broadly speaking insurers are unwilling to write cover that will give them any potential exposure to combustible cladding. This suggests that irrespective of a ban, insurers have already settled the issue as far as their PI policy holders are concerned.

We will be producing further guidance for members in the coming months.

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