Lesson 19 Overview

Welcome to Lesson 19. This lesson covers the Hurricane Wind Module overview.

At the end of this lesson you will be able to:

  • Explain key hurricane wind hazard concepts
  • Explain Hurricane Wind Module basic concepts and theory
  • Describe hurricane wind mitigation activities
Hurricane Wind Hazard Overview

A hurricane is an intense tropical weather system of strong thunderstorms with a well-defined surface circulation and maximum sustained winds of 74 mph or higher. Hurricane season in the Atlantic lasts from June 1st to November 30th; hurricane activity generally ramps up in August and peaks in early September.

Forecasting hurricanes and predicting their movement has become much more accurate as a result of technological advances such as increased meteorological surveillance using satellites and high-speed computers.

Table 1: Saffir-Simpson Hurricane Wind Scale

Hurricanes with sustained winds of at least 74 mph are assigned a category using the Saffir-Simpson Hurricane Wind Scale. The scale separates hurricanes into five categories based on wind speed and is used to estimate potential property damage.

Hurricanes of Category 3 and higher are classified as "major" hurricanes. Although not classified as major hurricanes, Category 1 and 2 hurricanes are still extremely dangerous.

The National Hurricane Center website: http://www.nhc.noaa.gov/aboutsshws.php provides a conceptual animation of wind damage associated with increasing hurricane intensity.

Category

Sustained Winds (mph)

Major

Category 174 - 95No
Category 296 - 110No
Category 3111 - 129Yes
Category 4130 - 156Yes
Category 5>157Yes
Hurricane Wind Classifications: Category 1

Category 1 hurricanes have sustained wind speeds of 74 to 95 miles per hour.

Damage could include the following:

  • Well-constructed frame homes could have damage to roof, shingles, vinyl siding, and gutters.
  • Large branches of trees may snap, and shallowly rooted trees may be toppled.
  • Extensive damage to power lines and poles could result in power outages that could last from a few to several days.
Hurricane Wind Classifications: Category 2

Category 2 hurricanes have sustained wind speeds of 96 to 110 miles per hour.

Damage could include the following:

  • Well-constructed frame homes could sustain major roof and siding damage.
  • Shallowly rooted trees could be snapped or uprooted and block numerous roads.
  • Near-total power loss is expected with outages that could last from several days to weeks.
Hurricane Wind Classifications: Category 3

Category 3 hurricanes have sustained wind speeds of 111 to 129 miles per hour.

Damage could include the following:

  • Well-built framed homes may incur major damage or removal of roof decking and gable ends.
  • Many trees will be snapped or uprooted, blocking numerous roads.
  • Electricity and water will be unavailable for several days or weeks after the storm passes.
Hurricane Wind Classifications: Category 4

Category 4 hurricanes have sustained wind speeds of 130 to 156 miles per hour.

Damage could include the following:

  • Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls.
  • Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas.
  • Power outages will last for several weeks or possibly months.
  • Most of the area will be uninhabitable for weeks or months.
Hurricane Wind Classifications: Category 5

Category 5 hurricanes have sustained wind speeds of >157 miles per hour.

Damage could include the following:

  • A high percentage of framed homes will be destroyed, with total roof failure and wall collapse.
  • Fallen trees and power poles will isolate residential areas.
  • Power outages will last for several weeks or possibly months. Most of the area will be uninhabitable for weeks or months.
Transcript: Hurricane Wind Module Basic Concepts and Theory

This video explains the basic concepts and theory of the Hurricane Wind Module of the BCA Tool.

The Hurricane Wind module analyzes the building performance of the structure being mitigated, specifically, its performance against a strong wind hazard associated with a hurricane.

Once the roof is blown off or damaged, or windows are shattered, wind can enter the structure. With the building envelope compromised, hurricane-force winds entering the structure will cause additional physical damage to the building and its contents.

To prevent these types of damages, the basic goal of hurricane wind mitigation projects is to harden the structure so that it performs better against strong winds. Hardening can be accomplished with project types such as installing hurricane straps that will better keep the roof attached to the structure, or hurricane shutters that will help prevent wind-borne debris from being blown through windows and doors.

To calculate project benefits, the hurricane wind module requires the following key data inputs. First is the windspeed data for the structure’s location. The windspeed velocity and frequency is critical to determining the calculated damages.

Next, you need to enter data about the structure that allows the tool to calculate an economic damage value, for example the:

  • Structure size in square feet,
  • Replacement cost per square foot, and
  • Whether the structure is residential or non-residential.

You will also need to provide more specific information about the building’s properties that the tool uses to determine building performance. These include:

  • The type of construction, which could be masonry, wood, steel, or concrete;
  • The roof cover type, which could be a gable or hip roof for residential buildings, or built-up roof or single-ply membrane roof for non-residential buildings; and
  • Whether the building has shutters.

The value of contents and displacement costs are also calculated as project benefits because the mitigation project will reduce or eliminate these losses. Finally, loss of function benefits can also be calculated as a project benefit for non-residential buildings.

With these BCA inputs known, it is possible for the tool to calculate the impact of the project on the structure’s wind risk. The dollar value of the reduced wind risk are the project benefits.

This concludes the explanation of the basic concepts and theory of the Hurricane Wind Module of the BCA Tool.

Hurricane Wind Mitigation Types Overview

As explained in the video on the previous page, the best way to mitigate the potential for losses due to hurricane wind is to “harden” the property and make it less susceptible to damage.

Mitigation project types that can be analyzed using the BCA Tool include:

  • Building Performance-related projects such as:
    • Shutters and impact-resistant glazing
    • Load path activities
    • Roof activities
    • Code plus activities
  • Non-Building Performance-related projects such as Acquisition

The following pages explain each project type.

Mitigation Type: Shutters

Project Description: Equip windows and doors with shutters, laminations, or other systems that meet the debris impact and wind pressure design requirements of the International Residential Code (IRC)/International Building Code (IBC).

This mitigation project assumes all openings of a building will be protected.

Purpose: To keep wind and rain out of the structure in order to reduce structural damage and damage to contents.

Mitigation Type: Load Path Activities

Project Description: Improve roof-wall connections using methods such as installing metal hurricane clips or hurricane straps.

Purpose: To improve the structural system of a building by providing a continuous load path from the roof to the foundation, which helps to prevent catastrophic roof uplift failures.

Mitigation Type: Roof Activities

Project Description: Improved Roof Sheathing Attachment is an example of a roof activity. This activity provides a better attachment of the plywood or oriented strand board (OSB) roof sheathing to the roof structure through appropriate fasteners. Closer fastener spacing helps to prevent sections of a roof deck from being lifted off by the wind. This reduces progressive failures and the penetration of wind and water into the building envelope.

Purpose: To secure the building envelope and building integrity during a wind event.

Mitigation Type: Code Plus Activities

Project Description: Typically refers to buildings that have been designed and constructed to withstand a higher wind speed than what is required in the code. If you select Code Plus as the project’s mitigation type, you cannot select additional mitigation types like roof improvements because those are included in Code Plus design.

Purpose: To exceed the local building codes and standards to achieve a greater level of protection.

Mitigation Type: Acquisition
Project Description: Acquiring and demolishing a structure and turning the property into open space in perpetuity. As with Code Plus activities, if you select Acquisition as the project's mitigation type, you cannot select additional mitigation options since the structure will be demolished.
Lesson 19 Summary

Lesson 19 covered the Hurricane Wind Module overview, including:

  • Key hurricane wind hazard concepts
  • Hurricane Wind Module basic concepts and theory
  • Hurricane Wind mitigation activities