Understanding facades and fire risk

25 Nov 2020

By Tudor Pop

glass office building
With not much to do on a wet Sunday than flick through the papers it’s hard to ignore the coverage of fire safety and building facades, which has been transformed from being a niche interest amongst property professionals, to a subject of concern to the whole country. As much as journalists try to condense fire safety into a punchy headline, the issue remains shrouded in nuance, detail and technical complexity quite apart from its political and social dimensions. The public discussion has moved on quickly from the immediate risks of ACM panels and rainscreen cladding and introduced new and equally opaque concepts like ‘relevant buildings’ and EWS1 forms.

So, what are the fundamentals that everyone should know?

What are the basic compliance obligations for new buildings?  The requirements – a set of performance characteristics - listed in the Building Regulations are mandatory for new buildings. Failing to satisfy a requirement is illegal. Guidance on how to comply with them is contained in the Approved Documents, a broader, more technical set of interpretive guidelines.

If the Approved Documents are followed, then a new building will more than likely comply with the regulations. The regulations are not retrospective but can apply to existing buildings if they are the subject of significant alterations.

What is a relevant building? Introduced in the 2018 amendments to the Building Regulations, relevant buildings have a storey at least 18 metres above ground level and contain one or more dwellings, an institution or a room for residential purposes. This excludes any room in a hostel, hotel or boarding house.

This definition is likely to change because the government’s Consolidated Advice Note issued in January 2020 suggests that it may move to include hotels, hostels and boarding houses in the ban on combustible materials in new buildings. It has also suggested that the ban may be extended to cover buildings with a storey at least 11 metres above ground level. This is a seismic shift in the number of new buildings that would be affected by the regulations.

What rules apply to relevant buildings?  Given the heightened risk in tall buildings, the regulations have been changed so that the performance-based requirements have been supplemented with prescriptive requirements that define the elements of a façade considered to be part of an external wall; this now also includes balconies. They also define how building heights should be measured, the allowable combustibility of materials that can be used in external walls and which materials are exempt.

So how does a new relevant building comply? The materials used for external walls need to be non-combustible, meeting the technical standards in EN 13501-1 classification A1, or classification A2-s1, d0.  The list of exempt materials is short and includes only items that have little significant fire load.

What is an external wall and what should be included? Some modern walls are designed as rainscreens where the external, visible part of the wall is largely weather protective and non-structural, so it’s often made from materials like high pressure laminate or metal panels. The cavity and insulation behind provide the necessary thermal performance. Some external walls can be built with masonry or precast components whilst the commonest form of backing wall construction today uses an internal structural framing system to support insulation and waterproof membranes.

The most common insulation products used in facades are made from various combustible materials ranging from expanded polystyrene and thermoset materials like phenolic, polyurethane and polyisocyanurate.  Non-combustible products such as mineral wool insulation, rock or glass fibre, are also used.

If a fire reaches a ventilated cavity-based system like a rain screen, fire propagation is rapid and unpredictable if it isn’t contained. This could be catastrophic. That’s why ventilated cavities should always contain horizontal and vertical cavity barriers to prevent and contain the spread of fire and smoke.

The Approved Document guidance for cavity barriers and fire stopping applies equally to relevant and non-relevant buildings. However, the Approved Documents don’t set limits on the combustibility of materials used in the external walls of non-relevant buildings. For these buildings, guidance is limited to the combustibility of the surface finishes of any cladding material.  That means that the cladding itself, or any underlying external wall elements material may be combustible.

Do I need to change how I carry out a fire risk assessment on an existing building? The government’s latest advice makes it clear that owners of multi-storey, multi-occupied residential buildings, (whether they fall into the definition of relevant or non- relevant under the Building Regulations) should include the risk of external fire spread as part of any fire risk assessment. Retrospective assessments will need intrusive investigation to verify the actual wall construction even if as-built drawings are available. These inspections might also reveal previously unknown defects which may cause fire risk assessors to adopt a cautious approach and demand these faults are remedied.

I keep hearing people talk about EWS1? For existing residential buildings taller than 18m the EWS1 (External Wall System) form is a new certification process. Introduced post-Grenfell, the form was designed as a quick way to provide lenders with the comfort they needed to progress transactions. The form defines five façade classifications which should be acceptable to lenders. All rely on a degree of technical analysis, some from a fire engineer. In some cases, if defects or non-compliance is revealed during inspections remediation works will be needed. The EWS1 process demands greater input from specialists, including fire engineers, and this can result in long delays in completing the assessment, especially where work is needed because it must be completed before the certificate is issued. Coupled with high demand, this has caused some sale transactions to be delayed or fail altogether.

To address the concerns about delay, on 21 November the government announced that the forms will no longer be necessary for buildings that don’t have cladding, following an agreement with the RICS, UK Finance and the Building Societies Association.  The government is also providing £700,000 to train more assessors.

Cladding in this context is now defined as aluminium composite material (often called ACM), brick slips, high pressure laminate, metal composite material, metal sheet panels, render systems, plastic tiling systems and timber or wood.

Is that it? I’m afraid not. New legislation is on the way too, in the form of the Building Safety and Fire Safety Bills both aimed at strengthening the ‘whole regulatory system’ for both building and fire safety.  Some tall buildings will fall into the higher risk category defined in the July 2020, Building Safety Bill. They will need to achieve standards of structural and fire safety so that risks to occupants are appropriately mitigated. Each building will need a formal Safety Case submitted for approval by the new Building Safety Regulator, part of the Health & Safety Executive. The Safety Case must be maintained and updated, as well as being available upon request. The Safety Case will consider all fire and structural aspects of the building, not just the external walls. Failure to comply will be a criminal offence, carrying a maximum penalty of up to two years in prison and an unlimited fine.

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