WHAT IS THE FIRE PERFORMANCE OF XPS INSULATION IN GROUND FLOOR CONSTRUCTIONS?

As one of the two main areas of building design and construction where extruded polystyrene (XPS) insulation is commonly specified, it’s useful to understand how ground floor constructions are viewed by national building regulations when it comes to fire safety.

A separate blog post deals with the difference between reaction to fire and fire resistance generally, while we have also looked in some depth at the fire performance of XPS insulation in flat roof build-ups. For information about the impact of the December 2018 revisions to the Building Regulations in England, check out this blog post.

Are ground floors classed as an ‘element of structure’ in regulations?

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 isn’t subject to these requirements.

What about internal fire spread and floor finishes?

Similarly, 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.

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 – but even where a combustible insulation material is installed above a concrete slab, it will not make the performance of the floor any worse in terms of fire.

Conclusions about ground floor fire performance

Discussions around the combustibility of building materials tend to focus on walls and floors – 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 compelling reason for them to.

However, it’s common to encounter a lack of confidence, awareness and understanding about how individual materials work together in complete build-ups. We therefore think it’s important to address the performance of ground and basement floors to allay any potential concerns at an early stage.

For more on the use of Polyfoam XPS products in different types of floor construction, visit our floor application pages. If those don’t answer your question, then contact us with any questions and we will get back to you.

Published in June 2019.

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