Wildfires have occurred with increasing frequency and intensity in locations that pose a risk to human life and habitation, with further escalation expected as climate change worsens. As such, designing bushfire-resistant buildings and even landscapes as a whole may become an urgent priority in some regions. This article will discuss some of the aspects that determine a building’s survivability during bushfires and how buildings and communities can be made more fire resistant.
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What factors affect building survival?
Vegetation
Ornamental plants and foliage in streets and around homes are major causes of wildfire spread into residential areas, especially where large trees overhang the property and there is no clear, non-combustible boundary, such as a wall. However, despite the availability of more fuel, forested areas are not particularly more vulnerable than areas with only low shrubs, as wind speeds are generally higher in these locations, promoting fire spread.
Post-wildfire analysis suggests that reduced vegetation within a 30-meter perimeter around a home improves the odds of survival, although some locations in California or Portugal, for example, require 60 and 50 meters of space in which Defend them, respectively. This includes making sure your gutters and vents are clear of leaves and other debris that could serve as a flashpoint from just a small ember or even just radiant heat.
Landscaping can also have a big impact on a home’s survivability, particularly its placement on a slope, and especially if there are plants underneath the building, as fire spreads more easily up a hill than in a flat landscape.
Construction arrangement
It has been found that the arrangement of houses and other buildings has an impact on the probability of destruction, and the worst cases are small, isolated groups of buildings that each have a significant peripheral connection to wild vegetation and are thus more vulnerable to wildfire.
Rural buildings are more likely to have less road access for emergency services and to be constructed of more flammable materials.
Building materials
Even the most densely populated areas remain at risk of property destruction caused by wildfires, particularly where flammable building materials such as wood are predominantly used, although larger building materials, cement, or other non-combustible materials act as a barrier to the spread. The fire. The structures at the heart of such developments are generally safe.
Among common building materials, stucco has proven to be superior to other materials such as masonry (brick), metal, and especially wood, while tile has proven to be a superior roofing material to shingles, metal, shake (wood), or composite (usually fiber glass/asphalt). During the Pedrogão Grande wildfires in Portugal, where construction was typically ceramic, 61.8% of the ignition points in missing homes were on the roof, and another 16% were on the windows. In this context, double-paned windows improve the home’s survivability, in addition to glass specifically designed to block radiant heat.
Study by Siffard et al. of wildfires in San Diego County, California, USA lists the factors most contributing to building destruction due to wildfires: building density, age of construction, location on a slope, presence of vegetation, overhanging vegetation, distance to major roads, and building materials. price et al. A similar conclusion was reached, although emphasizing defensible actions taken by residents, such as clearing vegetation or building walls, as homes that were defended during bushfires in eastern Australia were almost three times more likely to survive than those that were not. It is prepared in advance.
What steps can be taken to mitigate the risk of wildfires?
Homes specifically designed with bushfire resistance in mind can be made nearly impervious to direct fire damage, focusing first on the primary risk factors discussed above, namely clearing vegetation and creating a defensible area.
Roofs are classified in fire resistance from Class A to Class C, with the former being the most protective and typically constructed of materials such as clay, concrete and some types of asphalt. Roofs can be further fire-resistant with fiberglass or other chemical retardant coatings, while windows can be upgraded with double or triple-pane tempered glass, and walls with triple-coated plaster for maximum fire resistance.
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Covering vents with fine wire mesh that is too tight for embers to get through also blocks one of the most common ignition points, after the roof and windows. In a more extreme example of bushfire defense, specialized sprinkler systems can be installed on the roofs and perimeters of buildings that continuously flood the area when triggered.
More broadly, towns, cities and communities may need to be designed with bushfire defense in mind, as their severity and frequency are expected to increase in the coming years. Specifically, there is a need to focus on building larger communities with good defensible territories, minimal peripheral connectivity to wild lands, and excellent road access for emergency services.
Naturally, it is not desirable to remove large portions of vegetation surrounding populated areas, therefore, landscaping and tree planting decisions that cause potential wildfires can mitigate the risk of significant losses. For example, European pines have shown excellent fire resistance compared to many tree species, and they slow wind speeds and slow the spread of wildfires in low-shrub areas where they are grown.
Pine forests are commonly planted in areas affected by wildfires where they can grow successfully for these reasons and also provide the potential for future recovery of the area if further wildfires occur, due to the serotinous cones of many pine species. These cones are “glued” with a resin and can remain attached to the tree for many years as the seeds inside mature.
When a wildfire occurs, this resin melts, releasing mature seeds, which grow quickly in the nutritious soil. Many plant species depend on forest fires to release their seeds, and thus may be at risk due to excessive efforts to eliminate forest fires. However, the value of permitting and containing natural wildfires or engaging in controlled fires, i.e. removing brush and other flammable materials, in wildfire-prone areas has become increasingly recognised.
These types of strategies are likely to play the most contributing factor in defending populated areas from future wildfires, as their increasing incidence and impact on unprepared areas is unavoidable.
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References and further reading
Samora-Arvela, A., Aranha, J., Correia, F., Pinto, D. M., Magalhäes, C., & Tedim, F.. (2023). Understanding the construct of wildfire resilience: a multifactorial approach. fire, 6(1), 32. https://doi.org/10.3390/fire6010032
Fernandez, P.M., Vega, J.A., Jimenez, E. and Rigolot, E. (2008). Fire resistance of European pines. Forest ecology and management256, 3. https://doi.org/10.1016/j.foreco.2008.04.032
Siffard, A. D., Brennan, T. J., and Kelly, J. E. (2017). The importance of building materials compared to other factors that affect structure survival during wildfires. International Journal of Disaster Risk Reduction21. https://doi.org/10.1016/j.ijdrr.2016.11.011
