City of Lawrence
Neighborhood Resources Department
MEMORANDUM
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TO: |
Mike Wildgen, City Manager
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THRU: |
Victor Torres, Neighborhood Resources Director
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FROM: |
Barry Walthall, Codes Enforcement Manager
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Date: |
April 13, 2005
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The purpose of this memorandum is to respond to an information request from the Commission regarding low cost alternatives for storm shelters, community shelters for multi-family structures, and public education. Text in underlined blue font indicates an attachment to this memorandum.
FEMA provides design guidelines for the construction and manufacture of stand-alone shelters and internal shelters. Stand-alone shelters are separate structures; internal shelters are areas within or part of a larger building. The advantages of internal shelters (FEMA preferred alternative) are occupants don’t risk exposure to the elements to reach the shelter and can reach shelter more quickly and easily than having to go to a stand-alone shelter. In existing buildings, where retrofitting the structure to accommodate an internal shelter may be costly and/or technically infeasible, stand-alone shelters may be a reasonable alternative. FEMA provides construction details for storm shelters for construction or installation in single-family dwellings with capacity for up to 10 people, and for community shelters with capacities up to 90 people. Professional engineers can also use FEMA guidelines to design shelters with even greater capacity, and for multi-use functions, for instance a combination community recreation facility/shelter. FEMA design guidelines are intended to provide “near absolute protection” of shelter occupants, meaning that occupants will be protected from injury and death.
Several types of prefabricated shelters are manufactured for installation in newly constructed buildings, retrofit into existing buildings, or for stand-alone or in-ground applications. Prefabricated shelters are constructed of various materials, including pre-cast concrete, steel, fiberglass, and polyethylene depending on the application. Prices for pre-fabricated storm shelters range from $3,000 to $6,500 for small shelters with occupant loads of 4 to 10. The largest prefabricated shelter available was 8’ X 40’ X 7’, with an occupant load up to 60. The cost of this shelter, installed but not including shipping costs, was quoted as $34,000.
Safe rooms are a specific type of storm shelter constructed of steel reinforced concrete in existing or newly constructed above ground structures, typically one- and two-family dwellings. The State of Oklahoma and FEMA partnered to develop a program providing rebates to Oklahomans who construct above ground safe rooms or below ground storm shelters.
More than $3 million in rebates were made available to Oklahomans for the construction of safe rooms and storm shelters. FEMA delivered the funding, the Oklahoma Department of Emergency Management manages the program, and the employees of the Oklahoma City General Motors plant staff the Safe Room registration phone lines. The program provides a 75-percent rebate -- up to $2,000 -- to eligible Oklahomans who install above-ground safe rooms or underground storm shelters.
Funding is prioritized in four phases:
After Oklahoma's outbreak of tornadoes on May 3, 1999, the nation's first Safe Room rebate program was implemented. Through a partnership with FEMA, the 1999 program helped pay for more than 6,000 safe rooms, many of which are credited with saving lives in the May 8-9, 2003 tornadoes. In fact, there were numerous cases where a safe room was the only portion of a structure left standing after the May 2003 tornadoes and storms moved through Oklahoma.
As with private shelters, community shelters may be designed for single- or multi-function use. Single function shelters are designed and constructed solely for use as shelters, and may be stand alone or internal, and may be underground. The advantages of single function shelters are simplicity of design and building systems such as HVAC and electrical, and no space is lost to furnishings, storage, or contents unrelated to the shelter function. The advantages of multi function shelters include efficient use of building space and lower additional cost for a shelter because the space is used for other purposes. Examples of building spaces that may be utilized for shelter space include gymnasiums, cafeterias, exercise rooms, restrooms, and hallways.
FEMA’s “Community Wind Shelters Background and Research” is a ten page document summarizing the positive and negative aspects of various types of community shelters and also discusses required preparedness and maintenance issues, as well as containing information about hazard risk factors and determining the need for shelters.
According to data obtained from the National Weather Service, there have been 29 tornados recorded in Douglas County since January 1, 1950. These storms caused one death, 47 injuries, and 38.765 million dollars in property damage. Two of the tornados, June 19, 1981 and May 8, 2003, account for the one death, 82.9% (39) of the injuries, and 81% (31.4 million dollars) of the total property damage. Both of these tornados struck within the City. Most of the tornados, 23 of 29, resulted in no reported injuries or deaths.
FEMA developed Benefit Cost Analysis Software for tornado and hurricane shelters. The reports generated by this software contain a disclaimer that the results produced by the analysis are not conclusive evidence that the proposed project is cost-effective. The model was released in 2000, and is based on tornado data for Douglas County from 1950 through 1996. A benefit-cost analysis report is attached for a scenario in which a community shelter is constructed for a 100-unit apartment complex. The scenario assumes fluctuating occupancy rate depending on the time of day and maximum occupancy of 400; design wind speed 250 mph; shelter life of 30 years; average cost per square foot for shelter space $110.
A stand-alone single function community shelter constructed to accommodate the above scenario would require 2,000 square feet minimum shelter area and would cost approximately $220,000 to construct. The structure would also occupy space and would require appropriate site elements to serve the structure, such as accessible routes of entry, sidewalks and landscaping. The FEMA model projects the community shelter provided in this scenario would result in 2.27 lives saved and 6.76 injuries avoided in 30 years.
The model also provides projected financial benefits during the life of the shelter. The model projects injury costs to be $12,500 per occurrence, and death costs to be $2,200,000 per occurrence. The expected tornado benefits are $169,379 per year. Tornado benefits are the savings in injury and death costs over the 30-year life of the project. The net benefits are $151,150 per year. The net benefits are the tornado benefits less the construction costs. The total cost per year, amortized over 30 years, is $18,229.
There are numerous methods to provide storm shelters for multi-family structures. Ideally, shelter should be provided within the structure (internal type) to decrease the time it takes residents to reach shelter and eliminate exposure to the hazards associated with storms, such as high winds, flying debris, hail, rain, or lightning.
Internal shelters - Providing safe areas, such as bathrooms or hallways, or rooms within individual dwelling units, particularly when all dwelling units are constructed at least partially at or below ground level or when there are suitable common areas within the structure accessible to all residents. Such safe areas or rooms would be designed and constructed in accordance with the building code and FEMA design guidelines.
Single-function community storm shelters - Provide a stand-alone single purpose shelter, above or below ground. A single shelter could be provided for an entire apartment complex or multiple shelters could be provided depending on the circumstances. Advantages of this type of shelter are ease of design and economy of construction. Design and construction of building systems (electrical service, heating and air conditioning, and plumbing) are simpler and less expensive because only those features necessary for the operation of the shelter are provided. Disadvantages of this type of shelter are exposing residents to hazards associated with storms such as lightning, high winds, and hail, ensuring any residents with special needs or disabilities are accommodated, and ensuring the shelter is unlocked and accessible when needed. Also, these types of shelters have a tendency to be used for alternate purposes (such as storage) or not be properly maintained so when the necessity for shelter arises the shelter is not functional.
Multi-function community storm shelters - Provide multi-function community storm shelters. A community center or apartment complex office might be suitable for dual use as a shelter, if designed and constructed in accordance with the building code and FEMA design guidelines. Disadvantages of this option are exposing residents to hazards associated with storms, ensuring any residents with special needs or disabilities are accommodated, and ensuring residents are able to access the shelter or safe area after hours or any time staff is not on duty to unlock the doors.
Basements - Require basements with shelters or safe areas incorporated into the basement area for all multi-family structures. In order to provide “near absolute protection” as recommended by FEMA, providing a basement for shelter is not adequate. Although a basement, without a shelter or safe area meeting FEMA guidelines, may provide some level of protection, occupants sheltering in a basement are vulnerable to falling debris and risk being trapped under a collapsed structure. A properly constructed and equipped shelter in a basement would provide good protection.
Operations plans are an important component in assuring the functionality of community shelters when the need arises. Operations plans include plans to activate the shelter when appropriate, alert residents to take shelter, assuring the needs of people with special needs or disabilities are met, securing the shelter, monitoring the storm, and giving the all clear. Plans should also include provisions for year round maintenance of the shelter, public education, lists of emergency equipment and supplies to be on hand, and plans to restock or replace equipment and supplies as necessary. Any time a public or community shelter is required an operations plan should be required. There should also be provisions, such as annual inspections or readiness reports, to assure plans are being followed and shelters are properly maintained.
Habitat for Humanity “Strong Room” - Habitat for Humanity provides a “strong-room” for houses constructed in Lawrence. The walls of the room are constructed of doubled 2X4 wood studs spaced 16 inches on center and sheathed with two layers of ¾-inch plywood on the outer side of the wall and one layer of ½-inch gypsum board on the inner side of the wall. The wall is constructed with a double 2X4 top and bottom plates without joints except at corners, and is anchored to the floor with 7/8-inch diameter anchor bolts embedded 7-inches in concrete spaced 20-inches on center. The ceiling is constructed independently of the rest of the structure, with 2X6 wood joists spaced 16-inches on center. The joists are fastened with connectors to the wood stud walls, and the underside of the ceiling joists are sheathed with two layers of ¾-inch plywood. A solid core wood door with a deadbolt is provided for the door opening.
The construction for this room is modeled on FEMA design AG-5, Wood Frame Shelter Plan, Plywood and Steel Wall Sheathing. The FEMA drawing specifies the wall construction as constructed in the habitat homes, with the addition of 14 gauge steel sheathing between the two layers of plywood and the wood studs. The FEMA design also specifies the ceiling as constructed in the habitat homes, with the addition of 14-gauge steel sheathing covering the two layers of plywood sheathing on the underside of the ceiling joists. Rather than a solid core wood door, the FEMA design specifies a steel door, 20 gauge skin with honeycomb core, sheathed with 14 gauge steel attached with screws every 6 inches on center on the perimeter and 12 inches on center in field.
Habitat for Humanity modifies the design to eliminate the 14-gauge steel sheathing of the walls and ceiling; and uses a solid core wood door without sheathing in lieu of the steel door. This results in a room stronger than the rest of the structure, but does not meet FEMA guidelines and it is not assured inhabitants will be provided “near absolute protection”.
Wall Bracing Provisions of the Building Code - Another low cost construction method is provided within the building code. Braced wall panels are required by the code to improve the performance of light wood-frame constructed buildings in high wind conditions. Components of braced wall systems include anchor devices to fasten the wall panel to the foundation, bracing materials such as plywood sheathing or metal straps to strengthen the wall panel, and devices to fasten joists or rafters to walls. Locations and types of braced wall panels are prescribed by the code and must be denoted on plans received with building permit applications for new one- and two-family dwellings. Wind loading is factored into calculations for engineered structural designs for all occupancy types. Attached is an engineered garage portal bracing detail approved for general use on one- and two-family dwellings within the city. The Codes Enforcement Division began enforcement of these provisions in September 2002.
There are many avenues for public education available to the city including:
A thorough review of these avenues and the development of a comprehensive,
ongoing public education program could be accomplished with guidance from the
City’s Communication Coordinator.