The fire classification and the fire performance of external roofs are complex and often misunderstood issues, especially following the increase in legislation related to photovoltaic systems. The difficulties stem not only from the very nature of the materials and systems involved, but also from an unclear reference standard and a confusing approach to the performance statement.
Fundamental Concepts: Reaction to Fire and Fire Resistance
Before dealing specifically with the fire classification of roofs, it is necessary to clarify two key concepts: the reaction to fire of products and the fire resistance of building elements.
Reaction to fire: This is the classification of a product, once exposed to a fire source, to participate or not participate in the spread of flames. This performance derives largely (about 70%, if we want to place an educated estimate) from the material itself, but also, in part, from the type of installation and the surrounding elements (about 30%). The reaction to fire, therefore, is an intrinsic characteristic of the product, but it can be influenced by gluing, cavities or the presence of other combustible materials nearby. Under the Construction Products Regulation (CPR), this performance is usually declared in the Declaration of Performance (DOP), with a field of application that varies depending on the type of installation and interactions with other components.
Fire resistance: This classification concerns the ability of a partition element (e.g., a wall, floors and roofs, or a ceiling) to guarantee, for a given period, the stability and safety necessary to also allow the evacuation of occupants in the event of a fire. Fire Resistance classes are expressed by letters, e.g., "EI" followed by the number of minutes of resistance (e.g., EI 30, EI 60). This characteristic typically belongs to the entire separator system. It can also be declared for specific products only if they perform a separation function, such as doors or sandwich panels.
It is therefore essential to distinguish between reaction and resistance to fire:
Figure 1: Reaction to Fire of a material or product (LEFT); Fire Resistance of a separating element (RIGHT)
The first is primarily a property of the individual product, typically required for CPR
certification performance standards.The second relates to the whole system or separating element, typically associated with national fire safety regulations. Generally, CPR certification is not applicable when handling systems or product combinations, unless specified by a technical standard.
The Specificity of Roofs: A Basic Misunderstanding
In the case of external roofs, the required performance represents a mix of reaction to fire and fire resistance, thus creating significant confusion among manufacturers and other stakeholders in the sector. In particular, there remains uncertainty as to whether the performance is attributable to the individual product, e.g., the waterproofing element, or to the entire roof system, consisting of the insulation, vapour barrier and the deck.
This misconception arises from the fact that, while the CPR regulation requires that performance be declared for construction products, reality shows that fire behaviour often depends mainly on the overall system, not just the product.
The Two Components of Roof Performance
The EU fire performance of an external roof, according to EN 13501-5 and CEN/TS 1187, is
based on two main aspects:
Surface flame propagation: This aspect is closer to the concept of reaction to fire and depends about 70%* on the external covering material. The underlying substrate can also play a role, but secondary to the surface product.
Fire Penetration: This parameter closely relates to fire resistance. It evaluates whether flames can breach the separating element (the entire roof), thereby posing a risk of spreading to other compartments of the building. In this case, the external waterproofing element has little impact, while other components, such as the insulation and the deck structure, are decisive. In this case, we are in the opposite situation, with only 30%* of responsibility to be allocated to the surfacing product, with 70%* attributable to the overall roofing system.
*Note: The values of 70% and 30% are not exact figures; they are approximate numbers intended to illustrate the concept and provide a sense of scale.
This duality generates a constant debate between manufacturers and technicians, undecided on which area the performance of roofs should be declared and evaluated.
Figure 2: Surface flame propagation of a material or product (LEFT); Fire penetration through a
separating element, the roof (RIGHT)
Test Methods and Additional Complexity
The situation is further complicated by the presence of one test method, the CEN/TS 1187,
divided into four different sub-test methods for the fire classification of roofs, which evaluate different aspects. These include, in particular:
The T2 method, which focuses only on flame propagation and is more akin to reaction to fire and product certification according to CPR
The T4 method, on the other hand, mainly tests the penetration of the flame,
attributing more importance to the roof system rather than to the individual surface product, as normally done for Fire Resistance.
Therefore, it is not surprising if a roof rated Broof T2 exhibits fire penetration in practice, or if another with a Broof T4 rating shows significant surface spread during a real fire. On the contrary, this is completely normal.
In summary, with T2, 70% of the performance depends on the roof covering product, whereas with T4, the situation is reversed: only 30% is attributable to that type of product, and 70% to the system.
Note: The values 70% and 30% are not exact figures; they are approximate numbers meant to illustrate the concept and provide a sense of scale.
This confusion is also reflected in the photovoltaic sector, where the installation of panels
significantly changes the dynamics of the fire on the roof, especially regarding the surface spread of the flame.
