Resilient Design: Forest Fire and houses

Humans always love to live with nature. Only when we share our space with it, the natural world will be regarded as having a host of benefits for mankind. But when we try to intrude into the world, it leads to disasters. Such a disaster is the Forest Fire. At any given time, forest fires are raging around the world, from California to the Amazon to Australia. But unlike other disasters, it remains widely intact in the design of the built environment.

What is a Forest fire?

Wildfires or forest fires are uncontrolled, rapidly raging huge flames enhanced by wind or firebrands that can destroy a forest or a land area of vegetation within minutes. The estimate shows that the past decade has been most prone to this disaster.

The regions such as Taigan, African Savannahs, and dry forests of South Asia are integral to forest fires as to sunshine and rain. These regions are the Fire dependent ecosystems. When fires occur naturally in a forest, they are favorable in the way of making it fertile due to the neutralization of acidic soils and they recover quickly from the burns. Areas, where frequent and large fires occur, and cannot recover quickly, are known as Fire-sensitive ecosystems. Examples are tropical wet rainforests in the Amazon and Congo basins and Southeast Asia. 

House ignition: Causes and Effects

Human error is a major cause of forest fires, and their effects are devastating. According to the National Fire Protection Association, wildfires have destroyed thousands of houses annually in recent years. One of the misconceptions of home loss during forest fires is that the loss occurs when the main body of the fire passes. But houses do not ignite immediately by large flames. House ignition is the result of the growth of smaller fires, either in and around the home or a building. Some of the factors that cause home ignition are:

• Embers

Embers are the most important cause of house ignition. Embers, also known as firebrands, are light, but they can be blown through the air and result in the rapid spread of wildfire (known as spotting). Smoking a cigarette and not properly putting it out may seem to be habitual carelessness. But the embers of cigarettes are the leading cause of forest fires in many countries. These embers can spread and blow through the vents and windows and spread through the ignition of the vegetation or debris nearby.

• Direct exposure and Radiant Exposure

Near-home ignition will sometimes lead to the direct exposure of flames (the direct contact of flames to a building) or radiant heat exposure (the heat radiated by burning nearby). For instance, campfires that are unattended nearby homes may lead to radiant heat resulting in the ignition of homes, leading to forest fires. Similarly, when the houses are exposed directly to the heat produced by the burning debris (somewhere near houses), it leads to forest fires. Sometimes, irrigation fields nearby can also spread fire to the houses.

The effects of wildfires on homes are much more drastic. During fires, many homes are lost because the wildfire turns to urban fire, where the wildland to the home spread of fire, transforms to home to home spread, especially with decreasing separation between homes. The after-effects of wildfire include the change in the microclimate of the region and economic losses of people. The effects of smoke and dust also cause intense breathing discomfort, allergies, and respiratory disorders.

Resilient Design Strategies

Efforts to promote fire resilience in houses are lacking, because they are limited in scope and scale. Understanding the biophysical and social context of the fire-prone regions is an important part of identifying specific resilient strategies to forest fires. For example, homes densely packed within the matrix of flammable vegetation increase the exposure changing fire regimes (the pattern of fire), thus leading to a different treatment of resilience. Further, the soil and vegetation type, availability of water resources, and labor also determine the resilient strategies. 

The context level resilience strategies include:

1. Basic Resilience: Protect fires/ facilitate post-recovery.

Basic resilience includes allowing fire and vegetation succession to occur in settings where the exposure of valued resources is low and addressing the direct and indirect impacts of wildfires.

2. Adaptive resilience: Influence fire behavior/ characteristics of the built environment

To implement intensive vegetation management to reduce fire risk where human exposure to wildfire is high and changing climate and fuel conditions are moderate and to facilitate climate adaptation.

3. Transformative resilience: Transform ecological conditions to mediate the impacts of wildfires.

To implement a network of adaptive-resilience goals across multiple communities, redesign the character, location, and flammability of the built environment in regions with high exposure of valued resources to repeated severe wildfires, and accept and manage fire-catalyzed transitions.

The site-level strategies include:

• Climate and Vegetation

During the site selection for houses, consider prevalent vegetation types, climate, prevailing winds during the dry season, and the risk of accumulated vegetation that results in a fire. For example, planting oak trees upwind of a house and fencing around the house are effective defensive measures.

• Soil and Topography

Wildfire risks are not often limited to fires themselves. Soils destabilized by the loss of vegetation are highly vulnerable to flooding and mudslides. So we must consider whether slopes are steep that the earth could become unstable or configured such that floodwater and debris flows could damage a house.

• Neighborhood

Apart from considering the site, it is also important to consider the neighborhood for any vegetable debris and fuel loading and the soil properties. We shall also ensure our streets have proper driveways and vertical clearance for the easy access of emergency vehicles.

At the house level, the do’s and don’ts are:

1. Roof

1. Use materials with a class A rating. A roof made of metal or clay instead of wood shingles is less likely to ignite. 
2.  Roofs should always be clean from debris. 
3. Plug gaps can occur at the ridge of the roof leading to the easy spread of fires.
4. The gutter should be designed to shed the debris otherwise, it could be ignited by the embers. The gutters can also be filled with water as a pre-evacuation measure.

2. Windows and Vents

1. Open windows or vents are more susceptible to the entry of embers. At a minimum, ⅛” mesh should be used to cover the vents or windows.
2. Maintaining adequate defensible space from the vents and windows and using shutters can protect the house from fires.
3. Glass is the most vulnerable part of the window. Multi-pane glass will provide the most protection. Window screens can help the glass protect from radiant exposures.

3. Decks and Eaves

1. We need to pay special attention to the undersides of a balcony, a deck or an overhang, and even an underfloor area in a fire-prone zone. These are the areas where flames will be trapped due to high temperature and can spread easily to the other houses in the neighborhood. For example, storing firewood or any non-fire-resistant materials leaves the house at stake.
2. Decks could use paving stones instead of wood to prevent ignition.
3. Patios are often preferable to decks in wildfire-prone regions.
4. Eaves or overhangs should be wider to protect houses from rain, sunshine, and fires.

References:

1. Wilson, A., 2019. Fundamentals of Resilient Design: Designing Homes for Wildfire Resilience. [online] Resilient Design Institute. Available at: <https://www.resilientdesign.org/fundamentals-of-resilient-design-designing-homes-for-wildfire-resilience/>
2. Chai, C., 2021. Fire-Resistant Building Materials: 9 Ways to Build the Most Fire-Resistant Home – NewHomeSource. [online] NewHomeSource. Available at: <https://blog.newhomesource.com/design-fire-resistant-house/> 
3. Bernard, M., 2020. Wildfire Resilience Design Strategies for Architects and Homeowners. [online] Architect. Available at: <https://www.architectmagazine.com/technology/wildfire-resilience-design-strategies-for-architects-and-homeowners_o>
4. Arduman, E., 2018. Resilient Housing against a Tougher Climate- California Wildfires. [online] Medium. Available at: <https://emrearduman.medium.com/resilient-housing-against-a-tougher-climate-california-wildfires-71235928c00b>
5. Peters, A., 2018. Can we design neighborhoods to survive wildfires?. [online] Fast Company. Available at: <https://www.fastcompany.com/90266666/can-we-design-neighborhoods-to-survive-wildfires>
6. Ucanr.edu. 2021. Preparing Your Home – Fire in California. [online] Available at: <https://ucanr.edu/sites/fire/Prepare/Building/> 
7. McWethy, D., Schoennagel, T., Higuera, P., Krawchuk, M., Harvey, B., Metcalf, E., Schultz, C., Miller, C., Metcalf, A., Buma, B., Virapongse, A., Kulig, J., Stedman, R., Ratajczak, Z., Nelson, C. and Kolden, C., 2019. Rethinking resilience to wildfire. Nature Sustainability, 2(9), pp.797-804.
8. Quarles, S., Valachovic, Y., Nakamura, G., Nader, G. and de Lasaux, M., 2010. Home Survival in Wildfire-Prone Areas: Building Materials and Design Considerations.
9. Hirschberger, P., 2016. [online] Wwf.de. Available at: <https://www.wwf.de/fileadmin/fm-wwf/Publikationen-PDF/WWF-Study-Forests-Ablaze.pdf>