In a fire situation, the roof is a vulnerable building component depending on the type of material used
Whereas 2024 was generally a relatively good year in terms of the lower number of wildfires, this changed dramatically in September with the high level and intensity of fires that occurred in just a few days in that month.
Between September 15 and 19, 2024, Portugal faced an alert situation due to extremely adverse weather conditions, marked by high temperatures and dry weather, which increased the risk and number of rural fires in mainland Portugal.
During this period, 1,615 ignitions were recorded, with a peak of 451 ignitions on October 17, 2024. Prime Minister Luís Montenegro declared a state of calamity for the hardest-hit areas, mobilizing additional firefighters and other resources.
The total burned area exceeded 121,000 hectares, with over 100,000 hectares in the north and centre accounting for 83% of the total area burned in mainland Portugal up to that time.
The fires caused nine deaths (including three firefighters) and widespread disruption, including road closures, the destruction of dozens of homes, and school closures in several of the affected areas. The extreme weather conditions, including dry air and high temperatures, exacerbated the situation, making it difficult for firefighters to control the flames.
This illustrates that we can never be complacent or let our guard down when it comes to preparedness, in particularly the protection of our family or property. We do not know precisely when or where fires will occur, but those living in rural areas, particularly high-risk areas, should be prepared. Now is the time to start taking action to protect your property.
However, when we talk about preparedness, we instantly think about fuel management (namely land cleaning), but there is more to it than that, as this article shows.
ADAI (Association for the Development of Industrial Aerodynamics), at the University of Coimbra, is a private non-profit organization, and is the coordinator of the “House-Refuge” Project. Its purpose is to create guidelines for best practices in the field of construction. Aiming at the mitigation of the wildfire risk combining two components of the system – construction and the immediate surrounding area. This feature covers construction.
The impact of fires on buildings
The ignition of a building, resulting of a fire coming from outside, occurs primarily in two infrastructural components – the roof and the façades. In a fire situation, the roof is a vulnerable building component depending on the type of material used and the cladding itself.
Wooden structures and ceramic roof tile cladding are more susceptible to fire damage than concrete structures and metal tile cladding. However, in rural areas, almost a third of buildings have wooden/bamboo roofs covered in ceramic tiles. In fact, during the 2017 Pedrógão Grande fire, over 60% of the buildings burned were a result of flames entering through roofs, primarily between gaps in tiles.
Roofs and gutters – Commonly, new fires break out on the roofs of buildings, as burning leaves or embers carried by the wind tend to be deposited on them. To reduce the vulnerability of the roof in fire situations, it is crucial to choose fire-proof materials and carry out regular maintenance and cleaning of debris. This includes gutters as well, which should be regularly checked and leaves debris removed.
Walls/façade – The façade of a building can be itself a fuel provider in case of a wildfire. If the façade system, including cladding and/or insulation, is made of flammable materials such as wood, PVC panels or wood-plastic composites, it can increase the fire risk by contributing to the spread of flames and an increase in temperature, quickly endangering the building, its vicinity and its occupants.
Moreover, in buildings with façades which are less combustible, the burning environment will be less intense, and less smoke is produced – a slower and less intense fire spread allows for safer evacuation and more effective actions. This is especially important in rural buildings, where the residents are mostly elderly and have greater difficulty reacting to a fire situation.
Doors and windows – The high temperatures experienced in a fire situation affect the structural capacity of exterior doors and windows, causing them to degrade or even collapse, especially if they are made of wood or wooden frames, which are easily flammable in the event of a fire.
It is important to use fire-resistant materials in the construction of these elements. In addition, keeping doors and windows closed during a fire can prevent burning leaves or embers from entering the house and will reduce the intensity of any eventual indoor ignition.
Glass – The type of glass in doors and windows greatly affects the building’s vulnerability. The high temperature reached during a fire can cause the glass to fracture, creating openings that allow smoke, firebrands and heat to enter the home, facilitating the development of the fire inside. The action of the wind, which tends to be more intense during a fire due to the convective effects caused by the fire, can cause these fractures to break the glass. Although most buildings in Portugal have double-glazed windows, single-glazed windows are still common, especially in older buildings.
Shutters – Install shutters to prevent glass breakage: the use of shutters on the outside of doors and windows protects the glass. Shutters can be effective, but they have the disadvantage of being an active system because they require people to close them.
Blinds – Blinds are intended to provide shade when the weather is hot and retain heat on cold weather days. Blinds made of non-combustible material, such as steel or aluminium, whether hinged, sliding or roller shutter type, are suitable alternatives.
Screens – Use metal mesh screens to prevent glass breakage: The use of screens on the outside of doors and shutters to protect against insects is something that can be suitable for protecting doors and windows against the action of forest fires. One solution is for these screens to have metal mesh in good condition, without corrosion, with a mesh opening of less than 2 mm.
Garages – Flammable chemicals and materials are often stored in garages. In many cases, these garages are not completely enclosed and may have small air vents where sparks from a wildfire can enter.
Research presented so far indicates that during forest fires, most fires in buildings start through small ignitions. Ignitions progress slowly at first but can find conditions to progressively evolve throughout the building. If these small ignitions are prevented, fire damage to the home can be reduced and, therefore, controlling ignition sources is one of the basic premises when it comes to the preventive nature of fire safety.
More about the House Refuge Project here: https://houserefuge.adai.pt