Specification of materials for resisting fire spread over external walls.

Over the last few weeks and months I have had numerous conversations with fellow industry professionals, business acquaintances and colleagues, asking my thoughts about what materials can we or should we be specifying on projects and these questions are not just pertaining to what we know as HRRB’s (High Risk Residential Buildings), but are seeking clarification on buildings such as schools, offices, hospitals, etc., and irrespective of height.

In January 2020, the Ministry of Housing, Communities & Local Government (MHCLG) publication; 'Advice for Building Owners of Multi-storey, Multi-occupied Residential Buildings' was issued and stated that 'the Expert Panel has significant concerns that consideration is not routinely given to Requirement B4 of Schedule 1 of the Building Regulations, particularly where the guidance given in Approved Document B is not specific. Requirement B4 is clear and requires that "the external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the height, use and location of the building." THE NEED TO ASSESS AND MANAGE THE RISK OF FIRE SPREAD APPLIES TO BUILDINGS OF ANY HEIGHT.'

Essentially what this is saying to me is that compliance with the guidance given in Approved Document B should not be considered as conclusive evidence that a building is safe.

Compliance with the guidance given in Approved Document B is generally considered to be the minimum standard of building safety and there could very well be other factors that may need to be considered, such as;

- Employers Requirements – the Client/End User may have a specific requirement to exceed the minimum standards of the Building Regulations.

- Building Insurance requirements – Building Insurers may require materials to be LPCB (Loss Prevention Certification Board), FM (Factory Mutual), or UL (Underwriters Laboratories) approved.

- Fire Risk Assessment – the FRA might highlight a particular requirement under the Regulatory Reform (Fire Safety) Order.

The current versions of the Approved Documents which were published in December 2020;

- ADB1: Dwellings*; incorporating 2020 amendments – for use in England (* applicable to houses and flats, i.e. Purpose Groups 1(a), 1(b), 1(c)).

- ADB2: Buildings other than Dwellings**; incorporating 2020 amendments – for use in England (** applicable to buildings other than houses and flats, i.e. Purpose Groups 2(a), 2(b), 3, 4, 5, 6, 7(a), 7(b)).

- ADB1: Dwellinghouses***; incorporating 2020 amendments – for use in Wales. (*** applicable to houses, i.e. Purpose Groups 1(b), 1(c)).

- ADB2: Buildings other than Dwellinghouses****; incorporating 2020 amendments – for use in Wales (**** applicable to buildings other than houses, i.e. Purpose Groups 1(a), 2(a), 2(b), 3, 4, 5, 6, 7(a), 7(b)).

In order to meet the Functional Requirements of B4 of schedule 1 of the Building Regulations for resisting fire spread over external walls, depending on the type of building, the guidance can be found in the following sections of the Approved Documents;

- ADB1 (England) – Section 10.

- ADB2 (England) – Section 12.

- ADB1 (Wales) – Section 9.

- ADB2 (Wales) – Section 13.

For the purposes of explanation, the following narrative makes reference to the guidance given in Approved Document B2 (England);

The guidance set out in paragraph 12.3 requires that the external walls of buildings other than those described in Regulation 7(4) should either meet the guidance given in paragraphs 12.5 to 12.9, or should meet the performance criteria of BR135, using full scale test data from BS.8414-1 or BS.8414-2.

- 12.5 requires the external surfaces of the walls should meet the provisions in Table 12.1 (this replaces diagram 40).

- 12.6 requires that where the building has a floor level greater than 18m., that the insulation used in the external wall construction should be class A2-s3,d2 or better, i.e. of limited combustibility or non-combustible.

- 12.7 references best practice guidance for green (living) walls – Fire Performance of Green Roofs and Walls, published by the Department for Communities and Local Government.

- 12 8 requires that cavity barriers should be provided in accordance with Section 9, i.e. being provided at junctions of separating walls and separating floors with the external wall, around window and door openings, at edges of cavities, and to sub-divide extensive cavities greater than 20m. in any direction.

- 12.9 being specific to an external wall construction with a masonry or concrete inner leaf.

Where the building is a RELEVANT BUILDING, as described in Regulation 7(4), i.e. where the building has an occupied storey at least 18m. above ground level and which contains one or more dwellings, an institution, or a room for residential purposes (excluding a room in a hostel, hotel, or boarding house), the materials used in the construction of the external wall must comply with Regulation 7(2) such that they shall be Euroclass A2-s1,d0 or A1, classified in accordance with BS EN.13501-1, subject to the list of exemptions described in Regulation 7(3).

For the avoidance of doubt, the requirement of Regulation 7(2) DOES apply the following elements;

- Cavity trays used when NOT between two leaves of masonry (i.e. where used in SFS build-up’s) – stainless steel cavity trays are becoming widely available, but whilst they are appropriate for fire safety, they may well have a negative consequence with specific regard to thermal bridging (Part L compliance).

- Glass balustrade infill – laminated glass has a combustible interlay that bonds the sheets of glass together, so is not permitted for use. Toughened glass is non-combustible, but due to the potential of spontaneous breakage or accidental damage should not be considered as a viable alternative.

- Timber used in the construction of balconies is not permitted, irrespective of building height.

- Vapour Control and Breather Membranes used as part of the external wall construction should achieve a minimum of class B-s3,d0.

- Green (living walls) are not permitted on a RELEVANT BUILDING as they are considered to be a medium to the spread fire in hot/dry climatic conditions.