Building stronger buildings

The insurance industry gives homeowners and building owners incentives to fortify their structures

The International Hurricane Research Center, Miami, names the following 10 U.S. mainland areas as the most vulnerable to hurricanes:

  • New Orleans
  • Lake Okeechobee, Fla.
  • Florida Keys
  • Coastal Mississippi
  • Miami/Fort Lauderdale, Fla.
  • Galveston/Houston, Texas
  • Cape Hatteras, N.C.
  • Eastern Long Island, New York
  • Wilmington, N.C.
  • Tampa/St. Petersburg, Fla.

Recognizing the risks these areas face, the Insurance Institute for Business & Home Safety (IBHS) has focused its efforts toward increasing the resiliency of single-family homes. Founded in 1977 by U.S. property insurers, IBHS conducts research into and promotes effective measures for reducing losses associated with natural and man-made hazards to homes and commercial buildings.

To that end, the IBHS Research Center in Richburg, S.C., opened in October 2010. The test facility has been used to subject full-scale buildings to hurricane-strength wind and rain, fire and hailstorm simulations.


The research facility helped IBHS collect data to support its FORTIFIED Home™ program, which launched in 2000. FORTIFIED Home is a cost-effective means for homeowners to significantly improve their homes' resistances to damage from specific regional natural hazards. FORTIFIED Home is a third-party verification program that provides hazard-specific retrofit standards and protocols for documenting an initial evaluation and retrofit verification to obtain a FORTIFIED Home designation for an existing single family-home.

"IBHS positions FORTIFIED Home Hurricane and FORTIFIED Home High Wind & Hail for geographically different markets," says Tim Reinhold, Ph.D., IBHS's senior vice president of research and chief engineer. "FORTIFIED Home Hurricane is intended for Atlantic and Gulf coast states; FORTIFIED Home High Wind & Hail is intended for U.S. areas outside hurricane coast states."

IBHS states the program provides uniform, voluntary sets of standards that will help bring elements of existing homes up to current code requirements or, in some cases, where costs are low and benefits are high exceed code requirements. It further states a FORTIFIED designation is proof a home includes the key hazard protection features associated with the chosen level of protection.

FORTIFIED Home Hurricane and FORTIFIED Home High Wind & Hail provide prescriptive methods for incremental upgrades to home construction components. The upgrades are based on best engineering and construction practices developed from more than 20 years of storm damage investigations.

In addition to FORTIFIED Home programs for existing homes, IBHS established FORTIFIED for Safer Living® for new residential construction and FORTIFIED for Safer Business™ intended for new commercial construction.

Insurance industry regulations in some hurricane coast states require homeowner insurance policies provide premium discounts or credits to owners of one- and two-family dwellings that have received FORTIFIED designations.

In other hurricane coast areas, jurisdictions are enforcing building codes containing state or local modifications including upgrades similar to or based on FORTIFIED Home requirements.

A tiered approach

Field investigations of single-family homes have found a roof assembly typically is the most vulnerable portion of a home's construction during a hurricane or storm. Accordingly, FORTIFIED Home prioritizes upgrades that enhance roof assembly resilience. The roof assembly upgrades are prerequisites for further upgrades that address bracing for gables, protection for windows and doors, and structural connections for house-attached structures such as porches and carports.

The combined upgrades are necessary to reach the final tier of enhancements that address chimney securement; structural connections between the foundation, walls and roof; and additional requirements for skylights, windows and doors. A tiered approach allows homeowners the opportunity to gauge retrofit goals against their budgets and decide on the desired upgrade level.

FORTIFIED Home Hurricane and FORTIFIED Home Wind & Hail retrofit requirements overlap to a large extent, but there are differences related to the specific hazards each program is designed to address. Both program categories offer three levels of upgrade designations: Bronze, Silver and Gold. This discussion of FORTIFIED Home will focus on Bronze designations, which is the most common designation sought by homeowners.

New roof systems

FORTIFIED Home Hurricane Bronze Designation provides upgrades intended to minimize damage and loss resulting from a Category 1 hurricane. A Category 1 hurricane has maximum sustained wind speeds of 74 to 95 mph, according to the Saffir-Simpson hurricane scale.

A roof system replacement provides an opportunity to obtain a FORTIFIED Home Hurricane Bronze Designation. To qualify, the scope of work must meet specific program requirements in the following areas:

  • Roof deck attachment to the structural framing
  • Sealing the roof deck against water entry
  • Roof covering material and attachment classification for high-wind resistance
  • Attic ventilation material and installation classification for high-wind and water-intrusion resistances

Gable and gable overhang structural reinforcement and protection against water intrusion

The existing roof system has to be removed completely and the deck inspected for damage; any damaged roof sheathing must be replaced. Roof framing underneath damaged sheathing needs to be inspected and repaired if required. Guidelines for repairable damage and repair procedures are provided. Attachment of all roof sheathing is required to meet specific prescriptive requirements. For instance, any replacement plywood or oriented strand board panels need to be attached with 8d ring-shank nails spaced 6 inches on-center along all supports. Schedules for re-nailing existing roof sheathing are provided for common roof sheathing configurations.

Installing underlayment and sealing the roof deck against water entry into the attic are required. These tasks may be accomplished in one of several ways depending on the roof covering, available materials and local code requirements. A drip edge is required at eaves and rakes; at eaves, it may be installed over or under the underlayment.

If a roof has asphalt shingles, the entire deck may be covered with a self-adhering underlayment compliant with ASTM D1970, "Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection," and an application of Type I (15-pound) felt underlayment complying with ASTM D226, "Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing." The felt is intended to prevent shingles from bonding to the self-adhering underlayment, which could lead to damage of deck sheathing during a future tear-off.

Alternatively, all deck sheathing joints may be sealed with an application of a minimum 4-inch-wide self-adhering tape followed by an application of ASTM D226-compliant, Type II (30-pound) felt or synthetic underlayment fastened with capped ring-shank nails at prescribed spacing. Other approved methods are available for other roof system types. Underlayment must be sealed around penetrations and turned up a minimum of 6 inches at wall intersections and lapped by a wall weather barrier. Program requirements for asphalt shingle roof systems reference The NRCA Roofing Manual for flashing guidelines.

Roof covering material and attachment need to be classified for the nominal design wind speed for the location and site exposure. To meet this requirement, an asphalt shingle roof system with an appropriate high-wind resistance rating must be fastened according to the manufacturer's high-wind installation requirements. Asphalt shingle manufacturers include wind-resistance classification and installation instructions on shingle packaging. Also, starter strips and shingles along eaves and rakes must be adhered in a minimum 8-inch-wide application of flashing cement.

Exhaust attic vents (ridge vents, static vents, powered vents and turbine vents) are required to have passed Florida Building Code's TAS 100(A), "Test Procedure for Wind and Wind Driven Rain Resistance and/or Increased Windspeed Resistance of Soffit Ventilation Strip and Continuous or Intermittent Ventilation System Installed at the Ridge Area," and installed according to manufacturers' instructions. TAS 100(A) test information and installation instructions for qualified products commonly are provided in a Notice of Acceptance issued by Miami-Dade County Building Code Compliance Office, Product Control Division. This documentation may be found by searching a web-based registry at

Because gable vents are not designed to keep out water driven by hurricane-force winds, existing gable vents must be covered from the outside or inside. Structural wood sheathing cut to fit over the opening or nonporous shutters are fastened to the framing around gable vent openings and sealed around edges to meet this requirement.

Perforated soffit panels that provide intake air for attic ventilation have been found to fail during hurricanes because of inadequate attachment to roof framing and walls. These failures have led to additional substantial damage to interiors because water entered through the resulting openings. The program provides several prescriptive options for reinforcing or retrofitting soffit construction to minimize the risk of soffit panel blow-out during a hurricane.

Gables where roof sheathing overhangs the gable-end wall sufficiently that it requires support framing needs further reinforcing to meet program requirements. This gable configuration is associated with some of the highest wind pressures expected when a home experiences high winds. The prescriptive requirements provide for overhang framing (also known as outlookers) attachment to the gable-end wall and roof structure and reinforcing the gable-end wall with structural sheathing.

Existing roof systems

Depending on an existing roof covering's condition, it is possible to obtain a FORTIFIED Home Hurricane Bronze Designation without replacing the roof covering. The program requires an inspection to provide IBHS with information it requires to determine whether a retrofit is feasible. The general criteria for an existing roof covering are no visible signs of damage or deterioration and at least five years of useful life remaining.

If a roof assembly meets these criteria, spray polyurethane foam adhesive is applied within the attic to seal the roof deck and reinforce sheathing attachment. The adhesive is sprayed over all roof sheathing joints and along all framing edges where roof sheathing bears on the framing. The adhesive and installation are required to meet specific criteria. For instance, the adhesive, when used in these types of applications, is required to have demonstrated resistance to a design uplift pressure of at least 110 psf. Documentation of testing in accordance with TAS 202-94, "Criteria for Testing Impact & Nonimpact Resistant Building Envelope Components Using Uniform Static Pressure," is required to substantiate this performance.

Existing exhaust attic vents must be inspected to determine whether they are TAS 100(A)-tested and installed as recommended by the manufacturer. Vents that do not meet these requirements need to be replaced with TAS 100(A)-tested units and/or reattached.

Also, an application of adhesive is required behind the bottom flange of drip edge metal to improve its securement to fascia or roof edge trim. Typically, it is possible to install the adhesive without disturbing the existing roof covering.

High wind and hail

FORTIFIED Home High Wind & Hail Bronze Designation provides for upgrades intended to minimize damage and loss resulting from severe thunderstorms with wind gusts approaching 80 mph, Enhanced Fujita Scale Zero (EF-0) tornado winds and hail. The EF scale provides indirect wind speed estimates based on the degree of damage observed post-event.

This designation requires the same roof sheathing attachment and roof deck sealing enhancements for roof system replacement and retrofit as FORTIFIED Home Hurricane Bronze Designation. Roof system replacement is not required when there only is one layer of existing roof covering that shows no visible signs of damage or deterioration; has at least five years of useful life remaining; and is classified for impact resistance and the nominal design wind speed for the location and site exposure. Specific requirements for documentation are provided.

If a roof covering does not meet these requirements, the roof system must be removed and replaced using a new roof covering classified for impact resistance and appropriate high-wind resistance. In addition, regardless of whether the roof system is being replaced, all tree branches overhanging a roof need to be removed.

Administering the program

Homeowners can apply for a FORTIFIED Home designation on IBHS's website, Applicants are directed to a list of IBHS-accredited evaluators in their area to schedule a paid evaluation. A FORTIFIED Home evaluator is tasked with completing an inspection checklist and transmitting the information to IBHS, which will provide the applicant with a written report. The report includes an analysis of the home's current condition and identifies improvements needed to achieve each of the three FORTIFIED Home designation levels for the specified natural hazard.

The report is intended to serve as the basis for developing a scope of work required for the desired level of FORTIFIED Home designation. The homeowner is responsible for engaging a contractor to perform the upgrades. Compliance of this work with program requirements must be verified, and compliance documents must be submitted to IBHS by a FORTIFIED Home evaluator.

Once all the steps in the process are completed, the homeowner receives a FORTIFIED Home designation certificate that may be submitted to his or her property insurance provider as proof of compliance. The designation is valid for five years. If at the end of that period there have been no substantial changes to the home or condition of its critical components, the designation may be reissued for another five years following an inspection by a FORTIFIED Home evaluator.

The FORTIFIED Home evaluator training and certification program is administered by Architectural Testing Inc., York, Pa. Candidates need to document they meet experience and insurance coverage criteria and participate in training followed by a certification exam.

FORTIFIED certifications are available for roofing contractors, window and door contractors, and general contractors. The Construction Estimating Institute administers the FORTIFIED Home Contractor Certification Program.

According to Reinhold, as of February 2014, FORTIFIED Home Hurricane had about 600 completed projects with Bronze designations accounting for about 60 percent, Silver designations accounting for 15 percent and Gold designations accounting for about 25 percent of that number.

FORTIFIED Home Hurricane Gold Designation requirements for structural connections between the foundation, walls and roof are challenging to meet with many existing homes.

"Homes built after 2006 are good candidates for Gold designation because they were built to the new code that requires documenting continuous load path," Reinhold says. "With older homes, it is difficult to substantiate the existence of a continuous load path and, consequently, they likely require costly retrofits, which make them less attractive candidates for Gold designation. On the other hand, in hurricane-prone regions where engineering-based design is required and a well-enforced code is in place, it doesn't cost that much more for a new home to attain a FORTIFIED Home Hurricane Gold designation."

Financial incentives

IBHS's FORTIFIED Home program is recognized by property insurers in some states. For example, Code of Alabama, Section 27-31D-2 requires Alabama-admitted insurance companies to provide insurance premium discounts for single-family residential properties that have received FORTIFIED Home designations in Baldwin and Mobile counties.

And in Mississippi, House Bill 1410, Section 2 has similar provisions applicable to single-family residential properties in Hancock, Harrison, Jackson, Pearl River and Stone counties. Also, the Coastal Retrofit Mississippi project funded by a $27 million Federal Emergency Management Agency grant will pay up to 90 percent of the cost to retrofit single-family detached homes in Hancock, Harrison and Jackson counties using IBHS's FORTIFIED Home guidelines.

In addition, the Georgia Underwriting Association, formed to provide property insurance to Georgia property owners unable to obtain insurance in the voluntary insurance market, provides insurance premium credits for FORTIFIED Home designated properties.

And in 2010, the North Carolina Commissioner of Insurance approved rules addressing insurance premium credits for hurricane mitigation features on residential dwellings introduced by the North Carolina Rate Bureau (NCRB). NCRB is a state bureau responsible for promulgating rates for residential real property, private motor vehicles and workers' compensation insurance. The rules apply to residential dwellings located in 18 coastal counties insured under the state's Homeowners and Dwelling Policy Programs. Under the rules, residential dwellings that have received FORTIFIED designations are eligible for premium credits.

IBHS advises homeowners to contact their local insurance agents for additional information.

Building codes

The FORITIFIED Home program guidelines for upgrading roof assemblies' resiliences are guided in part by long-standing Miami-area code requirements. The FORTIFIED guidelines now are influencing building codes elsewhere.

Roofing practices that are part of FORTIFIED Home guidelines have a history of successful roof system performance in hurricane regions. FORTIFIED Home program guidelines for roof deck reattachment and adhering shingles along eaves and rakes in 8-inch-wide applications of flashing cement are similar to roofing practices that have building code requirements in Florida's Broward and Miami-Dade counties for more than 20 years. Roof deck reattachment and sealing against water entry have become statewide reroofing requirements with the adoption of the 2007 Florida Building Code.

IBHS is taking an active role in model code development. Three code change proposals advanced by IBHS were accepted by the International Code Council®'s (ICC's) Code Development Committee during 2013 ICC code hearings. Provisions based on IBHS proposals will be included in the International Residential Code,® (IRC) 2015 Edition. One of the new provisions recognizes an alternative underlayment application that consists of a minimum 4-inch-wide strip of self-adhering polymer-modified bitumen membrane compliant with ASTM D1970 installed over all roof sheathing joints and covered with an application of an approved underlayment sheet.

Also, codes adopted during the past few years in two Alabama jurisdictions (Baldwin County and City of Orange Beach) contain reroofing provisions based on FORTIFIED Home Bronze requirements.

Putting it to the test

IBHS investigated the effectiveness of FORTIFIED Home Bronze upgrades at its Research Center in August 2011. A full-size residential duplex was constructed for testing use. Deck sheathing seams were sealed with self-adhering tape over half the duplex. The seams over the other half were not sealed. An asphalt shingle roof system was installed and then blown off, exposing the deck on both sides of the duplex.

A series of tests measured water entry rates through soffits, gable vents and the roof deck. Then, furniture and appliances were placed inside the living space. The building was subjected to wind-driven rain at wind speeds up to 70 mph. Finally, IBHS brought in an experienced property insurance claims adjustor to estimate the amount of damage to each duplex half. The loss estimate for the side without a sealed roof deck was three times the loss estimate on the sealed deck side.

Homes constructed in accordance with FORTIFIED for Safer Living requirements were in the path of Hurricane Ike when it passed over the Bolivar Peninsula in Texas in September 2008. Thirteen FORTIFIED homes were built there in October 2000 when the program first launched.

It is estimated Ike generated maximum 3-second gust wind speeds of 110 to 115 mph in the area, maximum storm surges of 15 to 16 feet and a maximum rainfall rate of about 1 inch per hour during two periods of the storm.

Ten of the 13 homes remained standing with minimal damage. Other homes in the surrounding area were completely destroyed. Debris from homes swept off their foundations by the storm surge was responsible for destroying three FORTIFIED homes.

Inspection of the surviving homes revealed poor and inconsistent performance of ASTM D7158, "Standard Test Method for Wind Resistance of Asphalt Shingles (Uplift Force/Uplift Resistance Method)," Class H-classified asphalt shingles that were used. ASTM D7158, Class H shingles are considered suitable for use in low-rise residential construction in areas with a 3-second gust design wind speed of 150 mph. ASTM D7158 is referenced in the 2009 and 2012 editions of IRC for self-sealing asphalt shingle wind-resistance classifications.

IBHS has committed to thoroughly evaluating wind-resistance performance of asphalt shingles classified in accordance with standards currently referenced in model building codes. Work in this area began soon after the IBHS Research Center opened and continues.

Maciek Rupar is an NRCA director of technical services.

For an article related to this topic, see:
"Man-made hurricanes," February 2013 issue



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