Passive survivability refers to a building's ability to maintain critical life-support conditions in the event of extended loss of power, heating fuel, or water. This idea proposes that designers should incorporate ways for a building to continue sheltering inhabitants for an extended period of time during and after a disaster situation, whether it be a storm that causes a power outage, a drought which limits water supply, or any other possible event. The term was coined by BuildingGreen President and EBN Executive editor Alex Wilson in 2005 after the wake of Hurricane Katrina. Passive survivability is suggested to become a standard in the design criteria for houses, apartment buildings, and especially buildings used as emergency shelters. While many of the strategies considered to achieve the goals of passive survivability are not new concepts and have been widely used in green building over the decades, the distinction comes from the motivation for moving towards resilient and safe buildings.
Current issues The increase in duration, frequency, and intensity of extreme weather events due to climate change exacerbates the challenges that passive survivability tries to address. Climates that did not previously need cooling are now seeing warmer temperatures and a need for air conditioning. Sea level rise and storm surge increases the risk of flooding in coastal locations, while precipitation-based flooding is an issue in low-lying areas. In order for buildings to provide livable conditions at all times, potential threats must be realized.
Power outages In much of the developed world, there is a heavy reliance on a grid for power and gas. These grids are the main source of energy for many societies, and while they generally do not get interrupted, they are constantly prone to events that may cause disruption, such as natural disasters. In California, there have even been intentional power outages as a preventative measure in response to wildfires caused by power lines. When a power outage occurs, most mechanical heating and cooling can no longer operate. The aim of passive survivability is to be prepared for when such an event may occur, and maintain safe indoor temperatures. While back-up generators can provide some power during an outage, it is often not enough for heating and cooling needs or adequate lighting.
Extreme temperature Heat is the leading cause of weather-related death in the US. Heat waves coinciding with power outages puts many lives at risk due to the inability of a building to keep temperatures down. Even without a power outage, lack of access to air conditioning or lack of funds to pay for electricity also highlights the need for passive ways to maintain a livable thermal environment. One of the issues that passive survivability looks at is considering the many ways to keep thermal resistance of a building skin to prevent a room from becoming overbearing in the event of having a lack of access to standard temperature regulating systems. In the winter months, power outages or lack of a fuel source for heat pose a threat when there are cold fronts. Leaky construction and poor insulation result in rapid heat loss, causing indoor temperatures to fall.
Drought During a drought, the limited water supply means a community must get by using less, which may mean mandatory restrictions on water use. Extended dry spells can instigate wildfires, which add a heightened level of devastation. Drying clay soil can cause critical water mains to burst and damage homes and infrastructure. Droughts can also cause power-outages in areas where thermo-electric power plants are the main source of electricity. Water-efficient appliances and landscaping is crucial in water-scarce locations.
Natural disasters Natural disasters such as hurricanes, earthquakes, tornadoes, and other storm events can result in destruction of infrastructure that provides key electricity, water, and energy sources. Flooding after extreme precipitation is a major threat to buildings and utilities. The resulting electricity or water shortages can pose more of a threat than the event itself, often lasting longer than the initial disaster.
Terrorist threats Terrorist threats and cyberterrorism can also cause an interruption in power supply. Attacks on central plants or major distribution segments, or hacking of a utility grid's control system are possible threats that could cut off electricity, water, or fuel.
Passive design strategies There are many passive strategies that require no electricity but instead can provide heating, cooling, and lighting for a building through proper design. In envelope-dominated buildings, the climate and surroundings have a greater effect on the interior of the structure due to a high surface area to volume ratio and minimal internal heat sources. Internally dominated buildings, such as the typical office building, are more affected by internal heat sources like equipment and people, however the building envelope still plays an important role, especially during a power outage. While the distinction between the two types of buildings can sometimes be unclear, all buildings have a balance point temperature that is a result of building design and function. Balance point temperature is the outdoor temperature under which a building requires heating. An internally dominated structure will have a lower balance point temperature because of more internal heat sources, which means a longer overheated period and shorter under-heated period. Achieving a livable thermal environment during a power outage is dependent on the balance point temperature, as well as the interaction with the surrounding environment. A key aspect of all design for passive survivability is climate-responsive design. Passive strategies should be chosen based on climate and local conditions, in addition to building function.
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