In Smart-Timber™, the timber load-bearing structure is located within a multi-layer structural assembly and does not come into direct contact with fire.

Before fire can reach the structural timber, it must first pass through the layers that surround and protect it. This delays the direct exposure of the load-bearing structure to fire and high temperatures.

This protection represents the first stage of Smart-Timber™ performance in the event of fire. The next critical question is what happens if fire eventually manages to reach the structural timber itself.

From inside the home, before fire can reach the timber load-bearing structure, it must first pass through the fire-resistant gypsum board and then the OSB3.

The fire-resistant gypsum board used in Smart-Timber™ is 12.5 mm thick, manufactured in accordance with EN 520 and designed for applications with increased fire-protection requirements. Together with the other layers of the structural assembly, it is positioned between a potential internal fire and the structural timber, delaying direct exposure of the load-bearing structure to fire and high temperatures.

In a real fire, this delay is significant, as time is a critical factor for the safe evacuation of occupants and for timely intervention to contain and extinguish the fire.

From the exterior of the home, the structural timber in Smart-Timber™ is likewise not directly exposed to fire. Before an external fire can reach the timber load-bearing structure, the successive layers of the external building envelope are positioned in its path.

The external cementitious and acrylic layers, the certified expanded polystyrene (EPS) with a declared reaction-to-fire classification of Euroclass E according to EN 13501-1, and the OSB3 in accordance with EN 300 are all positioned before the structural timber.

Therefore, from the exterior as well, the structural timber is not the first surface encountered by the fire. This protection forms the first stage of Smart-Timber™ performance in the event of an external fire.

In Smart-Timber™, C24 structural timber is protected within the multi-layer structural assembly. If, after sufficient exposure, fire eventually manages to pass through the protective layers and reach the structural timber, a different stage of the system’s behaviour begins.

The surface of the timber begins to char progressively, from the outside inwards. Behind the charred layer, timber that has not yet charred remains and continues to contribute to the structural performance of the load-bearing structure.

This is what matters in practice: even once fire has reached the structural timber, its effect develops progressively rather than instantaneously. Charring and the remaining effective cross-section of the timber are parameters taken into account in structural fire design in accordance with EN 1995-1-2 (Eurocode 5).

In a real fire, this has direct practical significance: the period during which the load-bearing structure maintains the required structural performance is critical for the safe evacuation of occupants and for timely intervention to contain and extinguish the fire.

Whether a material is combustible or non-combustible is not, by itself, sufficient to determine the safety of a home in the event of fire. The essential question is how the complete construction behaves when exposed to fire and for how long it can maintain the critical functions for which it was designed.

This is why two different concepts must be distinguished. Reaction to fire concerns the behaviour of a particular material or product when exposed to fire and the extent to which it may contribute to fire development. Fire resistance, by contrast, concerns the ability of a complete building element to maintain its required functions for a specified period under fire conditions.

Neither “timber burns” nor “steel and concrete do not burn” is sufficient to assess the fire safety of a home. The relevant question is how the complete structural system behaves as the fire develops.

In ÖKOHAUS GER Smart-Timber™, we therefore consider two successive stages: first, how the structural timber is protected before it is directly exposed to fire and, second, how it behaves if fire eventually reaches it.

The fact that a structural material does not burn does not mean that it cannot suffer serious, even potentially devastating, damage in a fire. High temperatures affect structural timber, steel and reinforced concrete in different ways. The meaningful comparison should therefore not be limited to “which material burns?”, but should examine what happens to the load-bearing structure when the effects of fire and high temperatures eventually reach it.

In ÖKOHAUS GER Smart-Timber™, the C24 structural timber is initially protected by the layers surrounding it. If fire eventually penetrates these layers and reaches the timber, its effect develops progressively, from the surface inwards, through charring. This progression can be taken into account in structural fire design.

In steel structures, the steel may likewise be located behind appropriate protective layers. The difference, therefore, is not that Smart-Timber™ protects its load-bearing structure while a steel system necessarily does not. The critical issue is what happens when, despite this protection, the temperature of the load-bearing structure begins to rise.

Steel has high thermal conductivity and, as its temperature increases, its mechanical properties change and its strength and stiffness decrease. The temperature of the steel member and its effect on load-bearing capacity are therefore key parameters in the structural fire design of steel structures.

In reinforced concrete, the steel reinforcement is protected within the surrounding concrete. A severe fire, however, can affect both the concrete and its reinforcement, altering their mechanical properties and potentially affecting the load-bearing performance of the structural element.

The key conclusion for the homeowner is therefore different from the familiar “timber versus non-combustible materials” argument. All structural systems require appropriate structural fire design. In Smart-Timber™, the key lies in the combination of protecting the structural timber before direct exposure and its progressive, calculable behaviour through charring if fire eventually reaches it.