Building standards (fire safety) - external wall systems: consultation

Part 2: Definition and ban of category 3 metal composite material (MCM)

Overview

Following the ministerial working group on building and fire safety in March 2021, a need was identified to take precautionary action on both the highest risk cladding material and the use of large scale fire test results in new developments. Accordingly, as an interim measure and pending the outcome of this review, changes were made to Section 2 (fire) of the technical handbooks from 1 April 2021 to avoid use of the highest risk category 3 metal composite material (MCM) cladding in new building work and to remove reference to BS 8414/BR135 as alternative guidance.

A number of options where considered at the expert review panel March meeting including lowering the threshold of the calorific value of cladding materials from 35 to 20 MJ/kg. However, widening the scope to all cladding materials with a calorific value of 20 MJ/kg was not seen as a practical solution. Members agreed to retain as close to the existing definition used by Ministry of Housing, Communities & Local Government (MHCLG) as part of the aluminium composite material (ACM) panel screening test programme following the Grenfell Tower fire i.e. ACM (category 3) with a core material having a calorific value > 35 MJ/kg.

Questions 2 .1 & 2.2 below relates to the following definition of the highest risk thin MCM cladding panels. These panels are non-homogeneous products made from generally, aluminium, zinc or copper sheets around 0.5 mm thick bonded together with a variety of core materials which a range of calorific values. Market research has indicated that there are currently no MCM products on the market with an overall thickness of more than 7mm. However, markets can fluctuate and it is therefore important to decide for futureproofing if the ban on MCM should be within regulation (which is less practical to amend and requires parliamentary time) or be within guidance (which can be amended much quicker). The use of the word 'thin' and maximum 10 mm thick panels was also discussed at review panel meetings.

The following definition of MCM category 3 is proposed.

Any panel or sheet, having a thickness of no more than 10mm, which is comprised of a number of layers, two or more of which are made of metal, alloy or metal compound and one or more substantial layer of which is made of a material having a gross calorific value of more than 35 MJ/kg when tested in accordance with BS EN ISO 1716:2018 entitled "Reaction to fire tests for products – Determination of the gross heat of combustion (calorific value)" published by the British standards institution in 2018 and for these purposes a substantial layer is one which is at least 1mm thick or has a mass per unit area of at least 1kg per m².

Question 2.1: Do you agree with the above definition for MCM (category 3)?

Strongly agree ☐

Agree ☐

Neither agree nor disagree ☐

Disagree ☐

Strongly Disagree ☐

Please select only one answer and provide your reasoning in the box below. If you disagree or strongly disagree, please provide any suggestions below on an alternative definition.

Comments:

Question 2.2: Do you think that the ban on MCM (category 3) materials should be in guidance or regulation?

Guidance ☐

Regulation ☐

Unsure ☐

Please select only one answer and provide your reasoning in the box below.

Comments: