The supporting construction, otherwise known as the fire-separating element or substrate, is simply the wall or floor that supports the service penetration seal.
When it comes to understanding the limitations of your supporting construction, it is important to note that the firestop is only ever as good as the wall system (and vice versa!). If a plasterboard wall has a 30-minute fire rating and the services penetrating are firestopped using a fire collar with a four-hour fire rating, this does not mean the overall fire resistance will be four hours. It simply means that the wall would fail before the fire collar.
Therefore, you need to know at the early stages of the project what it is you want to achieve, and after collaborating with all the relevant, competent parties, how it is going to be achieved. The compatibility of the service penetration seal and the supporting construction, whilst understanding that it works as a system, will ensure the effective compartmentation of the building.
Furthermore, there are limitations when it comes to test standards for walls and floors. Onsite there are common wall and floor types that have been successfully fire tested, such as plasterboard walls and concrete floors. However, there are equally as many that may seem like the ideal solution for the project but may not have a tested application for service penetrations, for instance, CLT walls, plasterboard ceilings, and profile decks.
BS EN test standards define what needs to be tested, but also what is covered within the scope of application when that particular application is tested. Just like test standards have their limitations, so do supporting constructions. In very simple terms, testing an application is effectively a worst-case scenario which may cover a better-case scenario. Similarly, when we test flexible walls by one manufacturer that are classified to EN 13501-2, this covers other manufacturers’ wall systems that are also classified to this standard. In the same way, when you test plasterboard walls, the scope of application also covers rigid walls of the same thickness or greater, but not the other way around.
When choosing your supporting construction, it is recommended to take a system approach. This is where early engagement in firestopping is crucial as it ensures there is a level of flexibility in the design and allows the relevant manufacturer to understand your requirements more. It is better to change your plans at the design stage, rather than having to rectify mistakes during the construction of the building.
