2004 In-home-shelter-manual 26p.pdf

IN-HOME HURRICANE SHELTERING

PROTECT YOUR FAMILY

Building In-Home Retrofit Shelters

for Existing Houses

Introduction

Tornadoes and hurricanes are some of the most destructive natural disaster

causing phenomena. The state of Florida and other storm-prone areas have experienced a

considerable impact from storm damage due to the hazardous effects of high winds and

flooding from severe tropical storms and hurricanes. Table 1 and Table 2 list the

categories and associated damage levels of hurricanes and tornadoes, respectively,

provided by the National Hurricane Center (NHC). The tremendous increase in

population growth in recent years has resulted in the increased need for residential

construction, especially in coastal areas. Hurricanes such as Andrew and Opal have

illustrated the susceptibility of Florida structures to the damaging storm effects. The

growing concern for the state’s vulnerability to storm-induced damage has made

hurricane awareness and preparedness top priority for emergency management

organizations. Planning and preparing for hurricanes involves such strategies as knowing

risk areas, planning evacuation routes, preparing survival kits, protecting property and

observing hurricane advisories. In addition, emergency management suggests installing

in-house shelters with proper reinforcing

Who Needs a Shelter?

The state of Florida is located in a geographic area that experiences high storm

activity. The vast shoreline extending several thousand miles increases the storm damage

potential and vulnerability of residential structures along the coast. In recent years,

residents have suffered tremendous property damage and even loss of life due to

hurricane hazards. Most residential houses are constructed in accordance with

Table 1: Hurricane Categories and Typical Damage (NHC)

Category

Wind Velocity

Range

Typical Damage

74-95 mph

Minimal : No real damage to buildings. Some damage to

unanchored mobile homes and poorly constructed signs.

96-110 mph

Moderate : Some damage to building roofs, doors and

windows. Some toppled trees. Major damage to mobile

h omes.

111-130 mph

E xtensive : Some structural damage to small homes and

utility buildings. Large trees are toppled. Mobile homes are

destroyed.

131-155 mph

E xtreme : Extensive damage to roofs, windows and doors.

Complete roof structure failure on small homes. Some

curtain wall failure

156 mph and up

Catastrophic : Complete roof failure on many homes and

industrial buildings. Some complete buildings fail.

Evacuation may be required

Table 2: Tornado Categories and Typical Damage (NHC)

Category Wind Velocity Range

Typical Damage

40-72 mph

Minimal : Some damage to chimneys. Tree branches broken off.

S hallow rooted trees uprooted.

73-112 mph

Moderate : Peels surface off roofs. Mobile homes overturned.

Moving autos pushed off roads.

113-157 mph

S ignificant : Considerable damage. Roofs torn off frame houses.

Large trees snapped or uprooted. Light-object missiles

generated.

158-206 mph

E xtreme : Severe damage. Roofs and some walls torn off well-

constructed homes. Trains overturned. Most trees in forests

uprooted. Heavy cars lifted off ground.

207-260 mph

C atastrophic : Well-constructed houses leveled. Structures with

weak foundations blown off some distance. Cars thrown and

large missiles generated.

261-318 mph

I ncredible: Strong framed houses lifted off foundations and

disintegrated Automobile-sized missiles fly through the air in

excess of 100 mph. Trees debarked.

local building codes that may not take into account the effects of extreme winds

associated with hurricanes. For this reason it is imperative to take the necessary

precautions to secure your home and family from harm.

The objective of this manual is to provide design and construction guidelines for a

Retrofit Room, which is an in-residence shelter alternative geared towards existing

houses. Such a room will be able to withstand wind speeds up to 140 mph. Certainly, it

will be more preferable to have in-house protection than none at all. The in-house shelter

will offer significant occupant protection and reduce the demand on public shelters

during the events of hurricanes and tropical storms. The design criteria and construction

specifications for the retrofit room developed are based on the known performance and

strengths of existing materials and technology. Retrofit techniques make use of external

reinforcement for wall and roof sections of existing interior rooms to provide a

convenient and readily accessible shelter for residents. Its basis comes from post-storm

observations that show the tendency of interior rooms to remain intact even when the rest

of the house is damaged or destroyed.

Retrofit Room Design

The design of the Retrofit Room is specifically geared towards “typical” existing

houses in the state of Florida. Single-family residential houses with wood-framed or

concrete masonry structures on slab-on-grade foundations were chosen as model

buildings for the design. Shelter size and location of the retrofitted room depend on the

layout of the house. Feasibility and cost efficiency were the key factors in developing the

Retrofit Room technique for existing houses. Strengthening structural components with

external sheathing, extra members, additional anchorage and better connections were

some of the retrofit strategies selected to reinforce interior rooms. The materials most

capable of resisting the effects of debris impact, overturning and uplift were utilized to

provide adequate protection during the event of a storm. The primary criteria for

performance required that the entire room envelope stay intact throughout exposure to

extreme wind and debris impact.

One of the leading causes in building failure during high-wind events is the

failure of connections between building elements. It is mandatory to provide adequate

roof-to-wall and wall-to-foundation connections to ensure a continuous load path to

maintain the integrity of the structural system. Hurricane straps, anchor bolts and nails

are some of the connections used to secure the Retrofit Room and provide resistance to

uplift, overturning, and sliding caused by extreme winds.

The Retrofit Room design is based on wind speeds reaching 140 mph, which

accounts for the majority of hurricanes making landfall in the United States. Such

extreme winds have the potential to generate windborne debris with forces to penetrate

walls and roof systems. Because of the danger associated with flying debris, structures

located in hurricane-prone areas (regions with 120+ mph basic wind speeds) are required

to undergo debris impact testing. Florida Building Code debris testing specifications for

materials require that structural components resist penetration of a standard 2 by 4 in.

wood stud weighing 9 lbs striking on end at a speed of 34 mph. The Retrofit Room

design utilizes material combinations that will withstand missile impact.

Modifications to Existing Frame

In smaller houses that may not have exclusively interior rooms, it is necessary to

use at most two exterior walls in the design of the shelter. The exterior walls will

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