BEST
DESIGN
PRACTICES
FOR
WOOD
CONSTRUCTION IN TORNADO PRONE AREAS
FRAME
Vijaya Gopu1 and Marc Levitan2
ABSTRACT: An estimated 1,564 tornadoes have ravaged the U.S. this year and caused over 500 fatalities and untold
destruction to homes and other light-frame buildings. Tornadoes in the strongest category – EF5 and EF4 on the
Enhanced Fujita Scale – caused 75 percent of the deaths. Given the extensive loss of lives and destruction caused by
tornadoes, which typically account for nearly 60% of the annual insurance losses, the question does arise about the
current design practices for extreme wind loads. This paper addresses the challenges involved in designing tornado
resistant homes and the implications of any mandates to make home tornado proof. The best design practices for wood
frame construction in tornado prone areas that ensure occupants safety and reduce potential damage are discussed.
Emerging technologies for enhancing the performance of residential buildings in these extreme events are also dealt
with.
KEYWORDS: Tornadoes, wood-frame construction, design standards
INTRODUCTION 12
The devastation caused by tornadoes raise an important
question about the design standards and practices used
for residential construction which is primarily lightframe wood construction. Given the extensive damage
and destruction caused to homes by tornadoes (Figure 1),
shouldn’t the obvious solution be to design these
structures to be tornado-proof. This solution is neither
practical nor worth the expense. In order for a building
to be considered tornado-proof, the key components of
the building – roof , walls, windows, and doors – will
have to be missile resistant, i.e. capable of stopping
projectiles travelling in excess of 200 mph. Achieving
this level of performance would greatly increase the
overall cost of construction, a cost-prohibitive approach.
Alternately, the building will have to be completely
underground – not very practical -- to withstand winds
over 200 miles per hour. Even in tornado-prone areas
the chances of a tornado striking a particular home
during a life span of 50 years is only about 1%t. It’s
obvious that the solution to designing light-frame wood
structures in tornado-prone areas lies in the design of
these structures with improved wind resistance and with
the ability to protect the life of the occupants.
1
Vijaya Gopu, Department of Civil and Environmental
Engineering, University of New Orleans, and Louisiana
Transportation Research Center, 4101 Gourrier Avenue, Baton
Rouge, LA 70810, USA, Email: [email protected]
2
Marc Levitan, National Institute of Standards and
Technology, 100 Bureau Drive, Gaithersburg, MD 20899,
Email: [email protected]
There has been a very significant amount of research
done in the area of testing, analysis and design of lightframe wood structures subject to extreme wind loads.
Numerous technical articles and reports by government
agencies, wood products industry and research
laboratories/institutes provide guidelines for construction
of light-frame wood structures for resisting a desired
wind speed. Some states in the U.S. -- Florida and North
Carolina for example -- have implemented strict building
code standards to ensure a certain minimum level of
resistance to wind loads. Data collected after the
implementation of the stricter building codes have
clearly shown the significant reduction or absence of
wind storm damage in the newer buildings.
Figure 1: Before and After a Tornado Strike
Based on an extensive review of the state–of-the-art in
this area of design of wood structures for extreme winds,
this paper discusses the best practices for design of lightframe wood structures that have significant level of wind
resistance, result in a modest increment in construction
costs, and ensure occupants safety through incorporation
of tornado shelter within the structure.
WOOD FRAME CONSTRUCTION
DETAILS CRITICAL TO IMPROVED
WIND RESISTANCE
The impracticality of building tornado-proof light-frame
wood structures requires that design of these structures
focus on providing adequate resistance to withstand high
wind loads occurring at the fringes of a tornado. The
following details in wood frame are important to
ensuring the structural integrity of the building and will
be discussed in the full paper.
The design
recommendation for providing satisfactory vertical and
lateral load path for the structure and for achieving a
desired level of wind resistance will be discussed in
context of the construction details.

Roof sheathing attachment

Anchorage of roofs to wall and wall to foundation.

Nailing and anchorage of shear walls.

Anchorage of roofing material

Anchorage of gable ends

Impact resistant glazing

Anchorage of brick veneer to wood framing and
reinforced masonry walls.
The benefits of properly designed details and the
associated incremental cost for achieving a desired level
of wind resistance will be presented.
Overview of the engineered and prescriptive
requirements for wood frame construction recommended
by code bodies in the U.S. is presented. It is pertinent to
point out that while this design approach does not ensure
survivability when in the direct path of a tornado, it does
ensure a critical level of performance under extreme
wind loads.
TORNADO SHELTER
As mentioned earlier, the absence of tornado-proof
construction necessitates the incorporation of a tornado
shelter to ensure the survivability of the occupants.
Though it is well known that tornado shelters are critical
for survival when the building is in the path of a tornado,
they are not integrated into the structure in vast majority
of buildings built in the Tornado Alley of the U.S. It is
this absence of shelters that has caused the large number
of deaths this year. The breach of the building envelope
due to a missile or loss of a key component of the
building in a tornado results in an increase in the internal
pressure which coupled with the external suction forces
contribute to an immediate loss of the non-tornado-proof
structure. In such an occurrence, the occupants' survival
can be ensured only with the presence of a tornado
shelter within the building. The use of tornado shelters
away from the building is not desirable since use of these
shelters require exposure to potential flying missiles.
In this paper, the various shelters recommended in wood
frame structures will be discussed and their relative
merits are discussed. The shelters will include those
recommended by the Federal Emergency Management
Agency
(FEMA)
and
other
research
institutes/organization.
NEW TECHNOLOGIES FOR TORNADO
PROTECTION
Tornado-proof construction is a challenge with the
traditional wood frame construction used in the U.S. The
integration of new materials such as carbon fiber, metal
mesh and Kevlar in the building envelope hold the
promise of providing the protecting needed against
missiles flying in the air during a tornado event. These
new technologies will require radically new construction
concepts that provide improved tornado shelters or
possibly completely tornado proof buildings. These
technologies will be discussed in the paper.
REFERENCES
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"Testing a high-set house designed for 42 m/s
winds, Part I—Preliminary Results." Technical
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Testing Station.
[2] American Forest & Paper Association (2001)
Guide to Wood Construction in High Wind
Areas for One- and Two-Family Dwellings,
Washington, D.C.
[3] Federal Emergency Management Agency
(2008). Taking Shelter from the Storm:
Building a Safe Room for Your Home or Small
Business, FEMA 320, Washington, D.C.
[4] Federal Emergency Management Agency
(2000). Design and Construction Guidance for
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D.C.
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