Ground floors and ground floor insulation – what are the fire performance requirements?

Ground floors or basement floors – ‘the lowest floor of the building’, to use the terminology of Building Regulations – are not subject to the same fire safety requirements as external walls and roofs. However, uncertainty and risk aversion in design and specification can lead people to question whether certain build-ups or product choices are appropriate.

Buildings – particularly large buildings, non-domestic buildings, and buildings split into multiple uses and occupancies – can be incredibly complex. The more complex the building, the more specific the requirements in terms of fire safety and performance. This article is designed to address questions that designers, specifiers, installers and/or building owners and occupants might have about ground floor constructions, thermal insulation for ground and basement floors and their behaviour in a fire. Fire safety requirements as they relate to intermediate/separating floors are not in the scope of this article. None of the following advice is a substitute for following the guidance in regulations, or seeking advice from a fire engineer or other specialist. Some projects require consultation directly with the local fire service.

[edit] Which parts of national Building Regulations cover fire safety?

Building Regulations in the UK are primarily concerned with protecting the health and safety of people in and around buildings. They do not prioritise the protection of property, which is why insurer requirements can seem to go above and beyond what is required by the Regulations.

Technical guidance on fire safety can be found in the following documents, supporting the requirements of national Building Regulations in the different parts of the UK:

• England: Approved Document B, volumes 1 and 2.
• Wales: Approved Document B, volumes 1 and 2.
• Scotland: Section 2 of the technical handbooks.
• Northern Ireland: Technical Booklet E.

The aim of the Regulations in each country is broadly the same but the specifics of how those aims are achieved can vary. Essentially, Regulations deal with external and internal fire spread. They also cover access for fire and rescue services, means of escape and the fire performance of internal linings – although these latter three areas are not relevant to this article. Compliant fire safety design depends on building type, use, occupancy, layout, height and construction, as well as the distance from surrounding buildings.

[edit] How is the behaviour of individual products and element build-ups defined?

Assessing the fire performance of building elements generally means distinguishing between how individual components (such as an insulation board) behave, and how a construction element combining multiple components (such as a roof) behaves. For example, it is possible for a component with a poor individual test result to be safely used in a tested element build-up. When it comes to individual construction products, we are interested in the reaction to fire performance. For an element build-up or system, we are more interested in the fire resistance.

[edit] Are ground floors considered to be an ‘element of structure’?

A building’s structural elements are required to maintain stability in a fire, and resist fire spread from one part of a building to another. The way in which fires start and develop is largely independent of how a floor is constructed or specified. As a result, the lowest floor of a building is not considered to be an ‘element of structure’ as defined in Regulations, and therefore is not subject to those requirements.

[edit] Do floors contribute to internal fire spread?

The performance of floor surface finishes and linings, and their ability to resist internal fire spread, are not included in regulations because they make little contribution to the early development of a fire.

[edit] I would still like to understand the fire performance of products in my ground floor build-up

No problem.The European classification system is the standard method of declaring performance. Products are classified according to EN 13501-1, which measures how a product behaves when exposed to a fire, and how it contributes to the fire as it decomposes due to that exposure. From best to worst performing, the Euroclass system is: A1, A2, B, C, D, E and F.

For classifications from A2 to E, a designation for the production of smoke (s1, s2 or s3) and/or flaming droplets/ particles (d0, d1 or d2) is added.

[edit] How is the fire resistance of an element measured?

The fire resistance of building elements has three aspects, all measured by the number of minutes that elapse during standard tests for each.

• Resistance to collapse (R), which applies to load bearing elements only.
• Resistance to fire penetration (E), which is also referred to as integrity.
• Resistance to the transfer of excessive heat (I), otherwise known as insulation.

A construction element may need to meet all three aspects, in which case the performance would be written REI 30 (or 60, 90 or 120, depending on the period of resistance achieved/required). EI relates to an element that is not loadbearing, and sometimes E alone is required – again, both followed by the number of minutes. Classifications are determined from test data, in accordance with EN 13501-2 (construction products and building elements excluding ventilation services).

[edit] Is there a fire test for ground and basement floors?

As far as we are aware, there is no standardised fire test for the lowest floor of a building – not even an historical one. This is because of the lack of regulatory requirements concerning the fire performance of ground and basement floors.

There are only fire tests for separating floor constructions that contribute to a building’s compartmentation.

[edit] Conclusion

Discussions around the combustibility of building materials focus on walls and roofs as the main ‘elements of structure’ to which fire performance regulations relate. Ground and basement floor constructions have not become part of the debate, and there is no reason for them to do so.

Concrete slabs and screeds are, by their nature, non-combustible. For anybody concerned about the use of combustible materials in a building, an insulation layer covered by concrete poses no risk. Even where a combustible insulation material is installed above a concrete slab, it will not make the performance of the ground or basement floor any worse in terms of fire.

This article appears in the AT Journal issue 149 as 'Ground floors and ground floor insulation – what are the fire performance requirements?' dated Spring 2024 and Rob Firman, Technical and Specification Manager, PolyFoam XPS.

--CIAT

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