question: Why can't homes in tornado prone areas be built under ground?
comment: It is extremely expensive to build underground and a lot of the areas that are prone to tornadoes are also prone to flooding. It is not easy to build and maintain an underground house.
passages: Depending on location, various safe-haven areas have been prepared. The goal has been to avoid outer walls which might collapse when a roof section becomes airborne and the walls below lose their upper support: many interior rooms resist collapse longer, due to smaller walls interconnected to each other, while outer walls deflect the force of the winds. Because mobile homes typically lack foundation anchors and present a large surface-area sail (to catch wind), the advice has been to seek a safe haven elsewhere, such as in a stronger nearby building. When a mobile home begins to roll, people have been injured by hitting objects inside, or being crushed when a trailer suddenly hits the ground and begins to collapse around them.
   In a multi-story building, an internal stairway (away from broken windows) often acts as a safe haven, due to the stairs reinforcing the walls and blocking any major debris falling from above. If a stairway is lined with windows, then there would be the danger of flying glass, so an interior stairway, or small inner room, would be preferable.
   Many financial institutions outright exclude financing on earth-sheltered homes, or require this type of property to be common for the area.
  
  Section::::Comparison with standard housing.:Advantages.
  
  Section::::Comparison with standard housing.:Advantages.:Passive heating and cooling.
   It is recommended that people in the path of a large and violent tornado, whether referenced in a tornado warning or a tornado emergency, seek shelter in a basement, cellar or safe room, as stronger tornadoes (particularly those significant enough to warrant the inclusion of a tornado emergency declaration within a tornado warning) pose a significant risk of major injury or death for people above ground level. Those who do not have below-ground shelter are still advised to take cover in a room in the center of the home on the lowest floor, and cover themselves with some type of thick padding (such as mattresses or blankets), to protect against falling debris in the event that the roof and ceiling collapse.
   Wind engineering specialists from Texas Tech University's National Wind Institute have done extensive research that concludes that sheltering in an above ground storm shelter that meets the engineering criteria outlined in FEMA Pub. 320 and 361 and ICC/NSSA Standard for the Design and Construction of Storm Shelters is as safe as seeking below ground shelter during massive EF4 and EF5 tornadoes. TTU engineer Joseph Dannemiller presented the research findings at a TEDxTexasTechUniversity symposium in February 2014.
  
  Section::::Average storm shelter.:Below-ground shelters.
   In most instances rock bolting can replace the need for surface steel supports and the accompanying over-excavation to accommodate them, and it can avoid the need for separate concrete support of underground excavations.
   Section::::Drilled piles.
   Earthquakes happen when two blocks of the Earth's crust move relative to one another. The place where the blocks meet is called a fault, and faults tend to show up as relatively straight lines on maps. Any structure built directly on top of the fault will be torn in two when the blocks move. Constructing a building to withstand this sort of movement (often several feet in a matter of seconds) is not practical, so it is best to avoid building directly on top of an active fault.
   However, zoning restrictions may not deny an owner "any" economically viable use of his land. Suppose a "low density residential" zone requires that a house have a setback (the distance from the edge of the property to the edge of the building) of no less than 100 feet (30 m). If a particular property were only 100 feet (30 m) deep, it would be impossible to build a house on the property.
   The U.S. Federal Emergency Management Agency has spent tens millions of dollars subsidizing the construction of shelters and safe rooms in both private and public buildings. Many buildings in Tornado Alley do not have basements, because unlike in more northern areas, there is no need for a deep foundation to get below the frost line, in some places the water table is high, and expansion and contraction of clay-heavy soils can produce additional pressure on buildings that can cause leaks if not reinforced.
  
  Section::::Medical preparations.
   For comparison to NZS 4299 the following risk levels are based roughly on 0.2 second spectral acceleration (Ss) from 2% probability of exceedance in 50 years. Builders may refer to the Unified Facilities Handbook online for these values for some cities worldwide. These risk levels are based on ultimate strength, but deformation limits may require stiffer detailing or lower risk levels.
  
  Medium strength soil: unconfined compressive strength
  
  BULLET::::- ±0.75 g risk if 2 separate pieces of rebar are inserted, overlapped
  
  BULLET::::- 1.6 g risk if an entire internal rebar extends from base to bond beam
  
  Strong soil: unconfined compressive strength
   The "Joplin Globe" reported that 54 percent of the people died in their residences, 32 percent died in non-residential areas and 14 percent died in vehicles or outdoors. Joplin officials after the tornado announced plans to require hurricane ties or other fasteners between the houses and their foundations (devices add about $600 US to the construction costs). Officials rejected a proposal to require concrete basements in new houses. Officials noted that only 28 percent of Joplin's new homes had basements as of 2009 compared with 38 percent two decades before.
   Various hazards, ranging from hail to lightning can affect outside technology facilities, such as antennas, satellite dishes, and towers. As a result, companies with outside facilities have begun installing such facilities underground, in order to reduce the risk of damage from storms.
   Slab-on-grade foundations are commonly used in areas with expansive clay soil. While elevated structural slabs actually perform better on expansive clays, it is generally accepted by the engineering community that slab-on-grade foundations offer the greatest cost-to-performance ratio for tract homes. Elevated structural slabs are generally only found on custom homes or homes with basements.
   Individual wells along the U.S. coastline may also be required to have BOPs with backup acoustic control. General requirements of other nations, including Brazil, were drawn to require this method. BOPs featuring this method may cost as much as US$500,000 more than those that omit the feature.
  
  Section::::Deepwater Horizon blowout.
   BULLET::::- Possible resettlement - if concrete poured on top of poorly compacted soils it can still sink further. However, this is also possible with new concrete.
  
  Slabjacking can typically be broken down into three main process types:
  
  Section::::Slabjacking.:Mudjacking.
   The tornado continued a short stretch through the northwest corner of Morgan County, crossing Wheeler Lake, and into Limestone County, coming within approximately of Browns Ferry Nuclear Power Plant and toppling nearly a dozen high voltage power lines in Limestone County, snapping concrete power poles at their bases. These power lines delivered electricity from Browns Ferry Nuclear Power Plant, and without the outlet, the plant had to be shut down. The tornado continued towards the small community of Tanner.
   BULLET::::7. "Lack of Truss" - In this episode, which was also featured on "Marketplace" six months before it first aired, Mike and his crew visit homeowners who had asked for an additional bedroom, and were convinced by the original contractor that it could be done within the space of their attic. Yet, to do so, the original contractor had removed much of the structural support in the attic, forcing Mike and crew to remove the roof entirely to rebuild the bedroom, raising the height of the house in the process.
   One large undeveloped resource of wind in Ohio is Lake Erie. Its shallow depth and shelter from hurricanes provide advantages in terms of both ease of construction as well as safety of investment. Although land based wind farms frequently have lower siting costs, offshore wind farms usually have better wind, as open water lacks obstructions such as forests, buildings, and hills.
   Section::::Limitations, impediments and challenges affecting the development of Supportive Housing.:Lack of expertise in development and operations.
   Because some preparations vary, depending on location, people have been advised to consult their local area preparedness plans, rather than assume the plans are similar for all areas, such as which local buildings have been designated as storm shelters.
   In a later service assessment done by the NWS, it was determined that the school had taken the appropriate safety precautions to minimize and prevent potential loss of life with the tornado approaching, and the students were indeed in the safest part of the building. However, it was recommended in the assessment that hardened "safe rooms" with enhanced construction should exist, to prevent future disasters in the event of large and violent tornadoes impacting large buildings. A similar tornado on July 13, 2004 in Roanoke, Illinois, destroyed an industrial building, yet such rooms were used and no one there was seriously injured.
   Soldier piles are most suitable in conditions where well constructed walls will not result in subsidence such as over-consolidated clays, soils above the water table if they have some cohesion, and free draining soils which can be effectively dewatered, like sands.
  
  Unsuitable soils include soft clays and weak running soils that allow large movements such as loose sands. It is also not possible to extend the wall beyond the bottom of the excavation, and dewatering is often required.
  
  Section::::Specialty piles.:Screw piles.
   After Dan and Arthur escape from the basement of the leveled house through the collapsing floor beams where the first floor once stood, and look in awe of the rubble that was once the Hatch family's home, Arthur runs into Stacey and Ronnie Vae, who both survived the twister themselves in the Darlington's home (their parents were out of town on a trip back home to California at the time the storm hit). As Dan struggles to find his own family, Laura and Jenny are trapped inside the Salty Dawg (as they were taking cover inside, due to Jenny's 1992 Buick Skylark Gran Sport coupe malfunctioning), which also was destroyed by one of the tornadoes. Dan and Stacey then go save Dan's grandmother, Belle, at her farm; the two teenagers find Belle underneath wooden boards blown onto her from off of the partially damaged barn near her house (which itself survived intact).
   Historically, timber has been a plentiful, locally available resource in many areas. Today, timber piles are still more affordable than concrete or steel. Compared to other types of piles (steel or concrete), and depending on the source/type of timber, timber piles may not be suitable for heavier loads.
  
presuppositions: Homes in tornado prone areas can't be built under ground
corrections: Homes in tornado prone areas can be built under ground, however it is very expensive and difficult to maintain.
raw_presuppositions: Homes in tornado prone areas can't be built under ground Homes in tornado prone areas can't be built under ground
raw_corrections: Homes in tornado prone areas can be built under ground, however it is very expensive and difficult to maintain. Homes in tornado prone areas can be built under ground.