Bracing of Roofs for Hurricane, High Wind, and Seismic Resistance

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Roof dormer is braced with steel connectors and strapping to increase its resistance to uplift
Roof dormer is braced with steel connectors and strapping to increase its resistance to uplift
Scope

Roofs, roof projections, and dormers in new and retrofit construction can be strengthened by bracing with steel connectors and strapping to increase their resistance to uplift caused by high winds, hurricanes, and seismic conditions. Builders should consider installing the following:

  • Install steel connectors, strapping, or screws at roof-to-wall connections to increase the uplift resistance along the load path.
  • Secure roof sheathing to rafters or trusses using dense screw patterns, clips, and straps to increase the uplift resistance. 

This guide will focus on the products and techniques relevant to new construction. Please refer to the Solution Center guide Retrofit of Existing Roofs for Hurricane, High Wind, and Seismic Resistance for products and techniques that are more relevant to retrofitting existing homes.

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and EPA Indoor airPLUS.

Description

For homes located in areas that experience high winds, hurricanes, and high levels of seismic activity, roofs, and dormers, skylights, and other elements that project above the roof profile are vulnerable to damage. To protect a roof from the uplift forces, builders should consider installing the following: 1) metal structural connectors at framing joints, 2) sufficient bracing of walls and roof trusses, 3) increased fastening of roof sheathing, and 4) impact-rated glazing.

This guide will focus on the products and techniques relevant to new construction. Please refer to the Solution Center guide Retrofit of Existing Roofs for Hurricane, High Wind, and Seismic Resistance for products and techniques that are more relevant to retrofitting existing homes.

This guide will provide a discussion on dormer bracing because these structures are popular but they add many loads and stresses to the roof and structure of a home.

Metal Structural Connectors

For homes in high-wind areas, gone are the days when framing consisted simply of toe nailing and end nailing dimensional lumber together. Analyses of damaged buildings post-disaster have revealed that framing connections are usually the weak link causing a building to unravel during a storm or earthquake (FEMA 2010, 4.1). As a result, new standards have been developed requiring the use of steel structural connectors in the form of straps, ties, and screws to resist these extreme lateral, torsional, and uplift loads. In high-wind regions, special steel hardware connectors are used for most framing connections.

The use of steel connectors applies equally to the walls and roof of a dormer, which experiences extreme forces from wind pressures during a storm. An example of a dormer framed with steel connectors and strapping is shown in Figure 1 below. Additionally, dormers can add significant additional uplift and torsional loads to the main roof and the rest of the house. Turbulence and vortices from wind shedding off of a dormer can add additional forces to a building in addition to wind pressure (Cushman 2009).

The forces a structure is likely to experience are very region and location specific; therefore, it is imperative to research the building design conditions specific to the geographic location of the site and any special building codes that apply. Expected wind and earthquake loads impact the strength needed by the structural elements to withstand these loads and affect the required nail spacing patterns, wood sizing, and the number and types of structural connectors needed. The location also determines the level of corrosive weather exposure, such as salt spray, a connector will experience. This impacts the material and/or material coating selection.

There are hundreds of different steel connectors, brackets, ties, straps, and screws, each designed to resist forces from specific directions and magnitudes. While there are likely multiple connectors suitable for a specific connection, care should be taken to ensure an appropriate one is selected. The connectors in concert with the framing members must form a continuous load path, transferring the loads to the ground. Refer to this 2015 IBHS video for examples of the metal connectors used to form a continuous load path. A general illustration of the type of metal connector used for a particular situation can be found in FEMA P-499, Home Builder's Guide to Coastal Construction: Technical Fact Sheet Series. Specific diagrams and descriptions illustrating the correct connector for a particular situation can be found from manufacturer’s websites. The metal connectors must be installed according to the manufacturer’s or engineer’s specifications.

New connections are continuously being developed to strengthen connections that have been under-attended in the past. An example is the transition between the dormer roof and the main roof, which is framed with short jack rafters to create a valley. The compound miter angles of these rafters in the roof transition area necessitate a different kind of connector than straight rafters; thus, traditional rafter hangers cannot be used. Often there aren’t engineering specifications for the connection in this area or attention to ensure it is as strong and robust as all other roof connections. Because these rafters don’t have bearing/seat support, the lower nail fastener must provide that bearing. As a result, it is not uncommon to see split wood at this connection. Steel connectors have now been developed to address this connection and planning ahead can ensure a dormer is framed utilizing these connectors (Simpson Strong-Tie 2016). In high wind and hurricane regions, it is especially important to ensure that all parts of the roof are sufficiently strong since a partially damaged roof can result in significant water damage.

Since dormers add significant additional uplift and torsional loads to the main roof, care must be taken to ensure the roof framing around the dormer opening has sufficient strength to resist these loads. The 2015 International Residential Code (IRC 2015) provides framing guidelines for a roof or ceiling opening. It allows openings up to 4 ft to be created without needing extra framing members; thus, the header joist is permitted to be a single member the same size as the ceiling joist or rafter. A single header joist can be carried by a single trimmer joist if the header is located within 3 feet of the trimmer joist bearing. However, when the header joist span exceeds 4 feet, the trimmer joists and the header joist need to be doubled and of sufficient cross section to support the ceiling joists or rafter framing into the header. When the header joist span exceeds 6 feet, approved hangers are required for the header joist-to-trimmer joist connections. Tail joists over 12 feet long need to be supported at the header by framing anchors or on a ledger strip no less than 2 inches by 2 inches in cross-sectional area (IRC 2015 Section R802.9).

These guidelines should be treated as the minimum guidelines. For homes in locations with high wind, hurricane, and seismic conditions, adding additional bracing such as doubling the trimmer and/or headers may be required even for a small opening. The use of adhesives and metal strappings may be required to add strength and stiffness to framing. An engineer and local building codes should be consulted for location-specific guidance.

Roof dormer is braced with steel connectors and strapping to increase its resistance to uplift
Figure 1. Dormer is braced with steel connectors and strapping to increase resistance to uplift. (Home Innovation Research Labs 2012).

 

Roof and Wall Bracing

An increasing number of roofs are constructed using manufactured engineered trusses. These trusses can be designed with high heels to allow full insulation depth to be achieved along the eaves. However, raised heel trusses have been found in laboratory testing to experience high top cord and rotational displacement compared to a low heel trusses during lab-simulated seismic events (NAHB Research Center 2011). The installation of blocking and continuous sheathing around the raised heel mitigated these effects, pointing to the need to ensure that these measures to brace raised heel trusses are implemented in the field.

Trusses also need to be properly braced during installation to ensure safety and to ensure the trusses are installed straight and vertical. Trusses that are bowed or out of plum beyond the tolerances allowed by the manufacturer will fail to provide their designed strength because a truss is only strong when loads are applied in the directions it is designed for. To prevent trusses from buckling due to wind pressures, trusses need to be braced at the top and web cord with diagonal bracing. This bracing is especially important for securing the truss at the ends of a gable style roof. Every truss package will include specifications and installation guides on where to place the required bracing.

Wall bracing keeps a rectangular wall from shearing into a parallelogram shape when subjected to high winds and seismic loads. The amount of wall bracing needed, and the bracing method used is highly dependent on the location and shape of the building. Although a dormer only has to resist the forces imparted on its walls and roof, due to its height above the ground, it is subjected to higher wind speeds. The minimum length of qualifying braced wall is calculated based on seismic loads and then calculated again based on wind loads. The greater of the two values is selected. For a dormer with large window openings, there may be scenarios where there is not enough qualifying braced wall to satisfy the minimum requirements. If that is the case, an engineered design method is required. An engineer can specify specific steel connectors and braces that would result in the wall satisfying the required shear strength. The choice of wall bracing method is highly dependent on local codes. The International Residential Code (IRC) for example offers over a dozen choices, while the Wood Frame Construction Manual Guide to Wood Construction in High Wind Areas restricts the choice down to 3/8 in. or thicker OSB or plywood (IRC 2015; AWC 2015).

Secure Roof Sheathing

High winds lift a roof upward. This uplift force is transferred from the roofing material to the roof sheathing, then from the roof sheathing to the roof truss/rafters. Sheathing loss is one of the most common structural failures in hurricanes (FEMA 7 2010). To mitigate this problem, roofs in high wind locations typically use thicker sheathing panel and a tighter fastener spacing and ring shank nails. It is extremely important to use the level of sheathing quality and fastener spacing specified for the design conditions for small roof sections such as dormer and porch roofs.

Generic building code specifications for roof assemblies in high wind regions that factor in shear and uplift forces can be found in Chapter 7, Roof Assemblies, of the Standard for Residential Construction in High-Wind Regions (ICC 2014).

Impact-Rated Skylights and Windows

Hurricane-force winds can easily lift large heavy objects and turn them into high-velocity projectiles that can strike windows and skylights. A breach in the building envelope can not only cause severe water damage, it can significantly increase the wind loads on a structure. A breach in the building envelope on the windward side of the building will result in a significant positive internal pressure increase, which contributes to the uplift force on the roof. Homes are normally not designed to withstand these pressurization loads, which can cause a roof to blow off. This progressive failure can be prevented by protecting the glazing in the building envelope from being breached.

To protect against these flying projectiles, glazed openings (windows and skylights) should be protected by shutters or impact-resistant glass. The state of Florida for example requires storm shutters or impact-rated glass for homes located

  • Within the “wind-borne debris region” where design speeds are greater than 120 MPH or
  • Greater than 110 MPH if within one mile of the coast,
  • Except the Florida panhandle where the region lies within 1 mile of the coast, and
  • The “high velocity hurricane zone” of Miami-Dade and Broward counties.

The wind-borne debris region is defined as the “portions of hurricane-prone regions that are within 1 mile of the coastal mean high-water line where the basic wind speed is 110 mph (49 m/s) or greater; or portions of the hurricane-prone region where the basic wind speed is equal to or greater than 120 mph (54 m/s); or Hawaii” (FEMA P-762 2009).

However, even if a building is outside the required zone, it may be a good idea to have impact-resistant glass windows if it is located in a region that experiences high winds or hurricanes.

Glazed openings in buildings located in the windborne debris regions must be protected from windborne debris and that protection must meet the requirements of the Large Missile Test of an approved impact-resisting standard such as ASTM E1996 and ASTM E1886.

Impact-resistant glazing provides protection through the use of laminated glass or polycarbonate glazing systems. The use of physical-opening protection systems such as shutters, screens, or structural wood panels (as allowed by the IBC and IRC in certain hazard areas) is also a common means of achieving protection for glazing. Laminated glazing systems typically consist of assemblies fabricated with two (or more) panes of glass and an interlayer of a polyvinyl butyral (or equivalent) film laminated into a glazing assembly. After impact testing, the laminated glazing systems must resist the cyclic pressure tests of ASTM E1886 (FEMA P-762 2009).

How to Design and Specify Roof Connections in Locations Subject to High Winds, Hurricanes, and Earthquakes

Proper preconstruction design and specification is an essential step to success in designing a roof and roof projections that can withstand hurricane-force winds and seismic loads. This step includes:

  1. Ensure proper load path analysis and specification of framing and hardware capable of resisting those loads. Load paths must successfully transfer the uplift, torsional, and shear loads created by high winds from the roof to the foundation. Each connection and structural member can be thought of as a link in a chain; the chain must be continuous and is only as strong as the weakest link. See the Climate tab and the Compliance tab for more explanation on determining wind loads for your location per the IRC.
  2. Ensure adequate qualifying braced/shear wall paneling to keep rectangular walls from turning into parallelograms. Refer to the Wall Bracing guide for more details on wall bracing.
  3. Mark up the plans to specify the sheathing nail patterns and connectors to control uplift forces in the load path.
  4. Ensure all metal connectors used are fit for purpose and the correct fasteners are used for each metal connector. Fasteners specifically designed to be used with metal connectors are colored coded or have numbers stamped into the nail head to allow post-installation verification. The fasteners must go into the designed locations in the metal connectors. If a pneumatic nailer is used, it must be fit for purpose such as a positive placement metal connector nailer that has a probe/guide tip to ensure the nails are placed in the designed locations.

How to Construct a Dormer in High Wind and Hurricane Regions:

  1. Frame the roof opening for the dormer such that it has sufficient strength. Refer to engineering design specifications and local building codes for guidance. In the absence of these specifications, refer to the local adopted version of the IRC.
  2. Ensure the dormer walls are sufficiently connected to the main roof using metal straps to reinforce the studs in a dormer wall to the roof framing. Refer to engineering design specifications and local building codes for guidance.
  3. Ensure the dormer roof-to-wall connections are sufficiently strong using hurricane ties or other suitable metal connectors. Refer to engineering design specifications, local building codes, and the manufacturer’s specifications for details on the installation spacing. In the absence of further restrictions refer to IRC Table R802.11, Rafter or Truss Uplift Connection Forces from Wind (allowable stress design) (pounds per connection).
  4. Ensure the roof sheathing is sufficiently secured to the rafters through the use of adhesives, metal clips, and a dense nailing pattern that is in conformance to engineering design specifications or local building codes.
  5. Install skylights and windows that are impact-rated.

 

 

 

Ensuring Success

Generic residential building plans often lack specifications on sheathing nail patterns and connectors to control uplift forces in a load path. This is because the plans are designed to be applicable for a wide variety of geographic locations. Care must be taken to mark up the plans to specify these elements for a home built at a location susceptible to high winds, hurricanes, and earthquakes. Many building codes offices have spreadsheets on their websites available for download for calculating wall bracing requirements for seismic and wind conditions. Since the 2012 version, the IRC has included Table R802.11, which details the pounds of uplift force a roof truss or rafter connector must withstand for a given design wind speed, roof pitch, and rafter/truss spacing.

During construction, it is essential that there is adequate inspection and supervision for work quality. Site supervisors should inspect the construction to ensure that the fastener schedule and materials specified are adhered to and that all fasteners connect with framing members.

Climate

Generic residential building plans often lack specifications on sheathing nail patterns and connectors to control uplift forces in a load path. This is because the plans are designed to be applicable for a wide variety of geographic locations. Care must be taken to mark up the plans to specify these elements for a home built at a location susceptible to high winds, hurricanes, and earthquakes. Many building codes offices have spreadsheets on their websites available for download for calculating wall bracing requirements for seismic and wind conditions. Since the 2012 version, the IRC has included Table R802.11, which details the pounds of uplift force a roof truss or rafter connector must withstand for a given design wind speed, roof pitch, and rafter/truss spacing.

During construction, it is essential that there is adequate inspection and supervision for work quality. Site supervisors should inspect the construction to ensure that the fastener schedule and materials specified are adhered to and that all fasteners connect with framing members.

Wind Speed Maps

Wind speed maps contain contours specifying the wind speed a building must be designed to withstand for a specific location. Homes located within the wind-borne debris region have special design requirements. These maps occasionally change due to new data stemming from lessons learned from storms. For example, the wind speed map of Florida shown in Figure 1 shows the expanded region of homes that are subject to the design requirements of the wind-borne debris region shaded in green; buildings located in the area shaded in red were removed from being subjected to the designs requirements of the wind-borne debris region.

Florida Wind-Borne Debris Region, Category II and III Buildings and Structures except health care facilities.
Figure 1. Florida Wind-Borne Debris Region, Category II and III Buildings and Structures except health care facilities. (Florida Building Code).
 

Expanding the range of the wind speed map to the entire United States shows many regions that have special design requirements due to high winds as shown in Figure 2. 

Hurricane-prone and special wind regions of the United States.
Figure 2. Hurricane-prone and special wind regions of the United States. (FEMA P-804 2010).
 

To give some background to Figure 2, ASCE 7-05 defines windborne debris regions as hurricane-prone regions located within 1 mile of the coastal mean high water line where the basic wind speed is equal to or greater than 110 mph (and in Hawaii) and inland in hurricane-prone regions where the basic wind speed is equal to or greater than 120 mph. In ASCE 7-10, the windborne region is defined as locations where the wind speed is greater than 130 mph within 1 mile of the coast or any location inland where the wind speed is 140 mph or greater. Beginning in the 2012 International Building Code and International Residential Code, ASCE 7-10 is required for calculating the wind uplift pressures on buildings and other structures. Rather than using one design wind speed for all buildings, ASCE 7-10 assigns one of three design wind speeds for a location depending on the building's importance classification. Although ASCE 7-10 is more precise, the result is an actual reduction in geographic area that is subject to the building requirements of the hurricane-prone zone as shown in Figure 2.

Seismic Map

In addition to designing a building that can withstand high winds, the prescriptive design guidelines in the International Residential Code also take a building’s seismic risk into account as shown in Figure 3. The International Code Council assigns the seismic design category designation for a location based on research by the U.S. Geological Survey, which is summarized into probabilistic maps of the expected number of damaging earthquakes around the United States as shown in Figure 3. The IRC contours the U.S. into seismic design categories, from low risk to high risk as shown in Figure 4, which designates the categories by letter: A, B, C, D0, D1, D2, and E, with A designating the lowest risk and E designating areas with the highest risk. The IRC has design guidelines for categories A through D2 as well as scenarios for when a building in design category E can be reassigned to category D2. If a building located in design category E cannot be reassigned to category D2 then it must be designed using the IBC and not the IRC.

Probabilistic Map of Expected Number of Damaging Earthquakes around the U.S.
Figure 3. Probabilistic Map of Expected Number of Damaging Earthquakes around the U.S. (USGS 2014).
 
IRC Seismic Design Category Map
Figure 4. IRC Seismic Design Category Map. (IRC 2015).

 

Videos
Publication Date
Description
Video demonstrating and discussing continuous load path framing techniques from Remodeling Magazine.
Publication Date
Description
Video interview explaining the use of Simpson Strong Tie connectors for making walls and roofs more disaster resistant at a price of under $10,000. Recommendations from FLASH Strong Homes program.
CAD

Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

2018 International Residential Code

The IRC provides guidance on how strong a roof and wall needs to be to resist the positive and negative pressures induced by strong winds in Table 301.2(2) Component and Cladding Loads for a Building with a Mean Roof Height of 30 Feet Located in Exposure B(ASD). This table is used in concert with Figure 301.2(7) Component and Cladding Pressure Zones, to specify the minimum positive and negative pressures forces these different zones in a building need to be able to resist. For the roof decking, this resistance is provided by nails and screws. For the wall this resistance is provided though the combination of the studs, shear/brace wall technique employed, the wall sheathing if there is one, and the building’s siding material.

IRC on Roof to Wall Uplift Resistance Requirements:

Once you have the ultimate design wind speed, VULT, from looking it up on the ASCE 7 Hazard Tool, you can look up the rafter or truss uplift connection forces from wind in IRC Table R802.11 Rafter or Truss Uplift Connection Forces from Wind (Allowable Stress Design) (Pounds Per Connection) which has been included in the International Residential Code since the 2012 version. The IRC specifies when metal connectors are required in Section R602.3.5. However, for homes in hurricane and high wind regions, there are very few instances of a roof being small enough with rafters/trusses close enough together to not need metal connectors.

This table is useful for finding the uplift force a metal connector must resist to hold down a roof rafter or truss at a given ultimate design wind speed, roof span, spacing, and building exposure category. Once the uplift forces a metal connector must resist are known, one can look through a metal connector manufacturer’s catalog for products that meet or exceed the requirements.

IRC on Nail and Screw Fastener Requirements:

Fastener spacing and patterns are a very important component in a building assembly’s ability to withstand high winds and seismic loads. The IRC has specified the nail or screw size, length, and spacing for a specific building assembly across a few different locations in the document. The IRC specifies only screws to be used to fasten wood structural panels for walls located in the windborne debris area and the spacing of those screws is specified in Table R301.2.1.2. For exterior walls located outside of the windborne debris area, if they are sheathed with wood structural panels, the nailing pattern is specified in Table R602.3(3). The nailing pattern for roof sheathing can be found in Table R602.3(1).

IRC on Seismic Resistance Requirements:

The measures taken to strengthen a home to resist the uplift and bending/shear stresses induced by wind will also strengthen a home’s resistance to earthquakes. However, the strengthening measures and prioritizations will change depending on the location risk levels to earthquakes versus high winds. A home that is located in a high earthquake risk zone but one that has a relatively low risk of experiencing high winds will need to prioritize strengthening the foundation to resist shear forces and then working up the building as the budget allows. This can mean adding anchors, bracing posts, and foundation walls.

The IRC has a lot of guidance on building the different elements of a home so that they can resist seismic forces. This guidance is based on the seismic design category the home is located in. The categories are A, B, C, D0, D1, D2, and E, with E being the highest earthquake hazard risk. There are no special design requirements for seismic design categories A and B. The IRC has design guidance for categories C and D. Homes located in seismic design category E which cannot be recategorized into D2 via constraining provisions are also outside the design guidance scope of the IRC and must be designed according to the IBC. Details on the foundation can be found in IRC Chapter 4, floors in Chapter 5, and walls in Chapter 6. There are no seismic design prescriptions for the roof assembly because at the roof level, the controlling factor is wind forces.

IRC on Shear Resistance Requirements:

Shear and racking in buildings can be caused by wind and earthquakes. Braced walls are walls framed such that they are able to resist shear forces in a building. Section R602.10 of the IRC contains information about the minimum total length of qualifying braced wall panels along each braced wall line. There are tables to determine the minimum total length with respect to wind speed as well as seismic design category based on a home’s geometry. The IRC also contains information about the many different methods of wall bracing and what counts as a qualifying braced wall length.

Please reference your State or local adopted version of the International Residential Code for details on the current structural requirements. Local building code divisions are allowed to add requirements that make the building code stricter than the IRC.

Florida Building Code

Florida is notable for having the most stringent building codes in the U.S. with regards to building in high wind speed locations. The IRC contours Florida into a series of wind zones. The strength requirements for a building depend on the wind zone it is located in. The strictest wind zone, located in South Florida, requires buildings to be built to withstand 180 MPH winds.

Although wind zone standards were implemented in 1995, as many as 75% of the homes in Florida were built before such standards, leaving them vulnerable unless retrofitted (Powell et al. 2019). The Florida Building Code has special provisions for homes built in the wind-borne debris zone and the high-velocity hurricane zone.

For homes in the wind-borne debris zone but not in the high-velocity hurricane zone, the Florida Building Code has two options. 1. Design and build the home as “enclosed” with glazed openings protected by shutters or impact resistant glass. Or, 2. Design and build the home so it can withstand the combined external and internal wind pressures if the glazed openings fail (Florida Building Commission 2004).

The Florida Residential Building Code contains even stricter codes for buildings in the High-Velocity Hurricane Zone (HVHZ). All buildings in Miami-Dade and Broward counties, and those on the coast of Palm Beach county, are in the HVHZ and thus they are governed by even stricter codes. These include requirements for wall and roof cladding, surfacing, and glazing to be strong enough to resist a large missile impact. The large missile consists of a piece of 2x4 timber weighing 9 pounds impacting the test surface at 50 feet per second. The codes regarding residential construction in the high-velocity hurricane zone are detailed in Chapter 44 of the Florida Residential Building Code.

In the HVHZ, exterior stud wall sheathing must be thicker in order to resist not only racking/shear loads from wind but also the concentrated loads of a large missile impact from hurricane-generated wind-borne debris. As a result, the walls must be continuously sheathed by either diagonally placed boards not less than 5/8-inch in thickness, or plywood, or product approved structural panel rated for Exposure 1 with a minimum thickness of 19/32-inch. By comparison the IRC only requires a minimum of a 3/8-inch wood structural panel, which means it doesn’t need to be plywood. All products used in the HVHZ must be tested and approved. If glazing is replaced, the new replacement must be impact-rated. Additional details about the HVHZ product test procedures can be found in Section 1626 of the 2017 Florida Building Code.

2017 Florida Building Code, Section 2322.3 Storm Sheathing

Exterior stud walls shall be sheathed to resist the racking load of wind as set forth in Section 1620 and the concentrated loads that result from hurricane-generated wind-borne debris as set forth in Section 1626 of this code and shall be, at a minimum, any of the following types:

  1. Tightly fitted, diagonally placed boards not less than 5/8- inch (17 mm) thickness, nailed with three 8d common nails to each support for 1-inch by 6-inch (25 mm by 152 mm) boards and four 8d common nails for 1-inch by 8-inch (25 mm by 203 mm) boards.
  2. Wall sheathing shall be plywood, or product-approved structural panel, rated Exposure 1 with a minimum thickness of 19/32 inch (15 mm) and shall be applied to studs spaced not more than 16-inches (406 mm) on center. Wall sheathing shall be continuous over three or more supports and shall be nailed to such supports with 8d common nails. Nail spacing shall not exceed 6-inches (152 mm) on center at panel edges and all intermediate supports. Nail spacing shall be 4-inches (102 mm) on center at corner studs, in all cases.
  3. When plywood panel, or product approved structural panel sheathing is used, building paper and diagonal wall bracing can be omitted.
  4. When siding such as shingles nailed only to plywood or product approved structural panel sheathing, the panel shall be applied with face grain across studs.

Florida Building Code Window Glazing Impact Testing Standards

Glazing that is impact-resistant must pass tests detailed in the following standards:

If a product passes the three Testing Application Standard (TAS) standards below then it is approved for use in the High-Velocity Hurricane Zone (Miami-Dade and Broward counties).

  1. Florida Building Code: TAS 201 Large and Small Missile Test Standards
  2. Florida Building Code: TAS 202 Uniform Structural Load Standards
  3. Florida Building Code: TAS 203 Uniform Cyclic Pressure Test Standards

Products that pass the ASTM E1886 and ASTM E 1996 standards are approved for use in the Windborne Debris Regions (ICC 2017 FBC).

  • ASTM E 1886 Standard Test Method for Performance of Exterior Windows, Curtain Walls, Doors, and Storm Shutters Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials
  • ASTM E 1996 Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Storm Shutters Impacted by Windborne Debris in Hurricanes. The ASTM E 1996 indicates what missile size shall be used depending upon application and wind speed, location of impact, pass/fail criteria, and substitution limitations.

The Miami-Dade County TAS Standard is more stringent in that it does not allow the test missile (9-pound 2x4 at 34 mph) to penetrate the unit or protective system and does not allow it to break the glass behind the protective system. The other standards allow the test missile to penetrate the protective system provided the opening does not increase in size as it is subjected to wind pressures and so long as after all the testing is completed, the hole is small enough so that a 3-inch diameter sphere will not pass through the hole. Videos of these test being conducted on skylights can be found on the YouTube channel of Kingspan Light & Air LLC, a manufacturer of skylights.

IBHS FORTIFIED Home

The Insurance Institute for Business & Home Safety created an above-code program called FORTIFIED Home. Fortified Home contains a long list of above-code requirements pertaining to load paths, wall impact resistance, window impact resistance, roof strength, and more. The program has tiers for whole house certifications and a certification for just the roof. Thus, a home could be built with just a roof that meets the FORTIFIED Roof requirements. Once inspected, the home would receive a certification that it has a FORTIFIED Roof. The FORTIFIED Home program also has tiered whole house certifications for the Fortified Roof, Silver, and Gold levels. The program has requirements for new homes and existing home retrofits and the certifications are valid for 5 years. Certifications can be renewed for another 5-year term after an inspection.

The FORTIFIED Roof criteria requires the roof decking to be attached with a minimum of 8d smooth-shank nails spaced nominally at 4 in. o.c. along all framing members or 8d ring-shank nails at 6 in. o.c. along all framing members. This is an improvement over the IRC, which only requires 8d smooth-shank nails at 6 in. o.c. along the edges and 12 in. o.c. on the intermediate supports (IRC Table 602.3(1)). The roof covering must be high wind rated. For existing roofs where the roof deck nail pattern cannot be adequately verified, attic access is required to apply a 2-part spray-applied polyurethane foam adhesive to the underside of the roof at all joints between sheathing and at all intersections between roof sheathing and roof framing members, and at all valleys to secure the roof sheathing. For new roofs, the FORTIFIED Roof program requires the roof deck to be sealed to keep water out in the event the roof covering is damaged during high winds. Additional information about FORTIFIED Roof and the FORTIFIED Home requirements can be found at the FORTIFIED HOME website. As of June 2020, there are 18,000 homes in the U.S. that have received a FORTIFIED certification (IBHS 2020). While this is a commendable achievement, this still leaves many homes without these above-code fortification features. For comparison, more than 2 million homes in the U.S. have been certified to ENERGY STAR.

Metal Connector and Fastener Manufacturer’s Manuals

The steel structural connector used for the specific application must be fit for purpose. Documentation from an engineer or manufacturer’s literature should be available to demonstrate the steel structural connector used is fit for purpose. The strength of steel structural connectors is dependent on the fasteners used to secure them. As a result, each connector has specifications about the nail size it must be used with. Nails used for metal connectors often either have size information stamped on the nail head or color-coded nail heads to allow for post-installation inspection verification. Manufacturers such as Simpson Strong-Tie have extensive catalogs and documentation on the use and tested strengths of each of their structural connectors.

This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.

Existing Homes

Information regarding bracing roofs in existing homes can be found in the guide  Retrofit of Existing Roofs for Hurricane, High Wind, and Seismic Resistance.

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References and Resources*
Author(s)
International Code Council,
Florida Building Commission
Organization(s)
ICC,
FBC
Publication Date
Description
Florida building code including all the amendments and additions by Florida for the wind-borne debris regions and the high-velocity hurricane zone.
Author(s)
Home Innovation Research Labs
Organization(s)
Home Innovation Research Labs
Publication Date
Description
Fact sheet describing how to install bracing to retrofit roof dormers for increased wind resistance.
Author(s)
Cushman
Organization(s)
The Journal of Light Construction
Publication Date
Description
Article describing how adhesives can be used to make homes in high-wind locations stronger and how adhesives could be too effective resulting in overloading foundation anchors under earthquake loads.
Author(s)
Federal Emergency Management Agency
Organization(s)
FEMA
Publication Date
Description
Technical fact sheet highlighting important building connections and illustrating the proper use of various types of connection hardware; also published in FEMA P-499 “Home Builder’s Guide to Coastal Construction: Technical Fact Sheet Series.”
Author(s)
Federal Emergency Management Agency
Organization(s)
FEMA
Publication Date
Description
Fact sheet providing information about proper roof sheathing installation and illustrating fastening methods that will enhance the durability of a building in high-wind areas; also published in FEMA P-499 “Home Builder’s Guide to Coastal Construction: Technical Fact Sheet Series.”
Author(s)
Simpson Strong Tie
Organization(s)
Simpson Strong Tie Structural Engineering Blog
Publication Date
Description
Article describing a steel connector product for jack rafter connections.
Author(s)
Kapur,
Mahadevia,
Park,
Passman,
Perotin,
Reeder,
Seitz,
Sheldon,
Tezak
Organization(s)
FEMA
Publication Date
Description
Report providing guidance on how to improve the wind resistance of existing residential buildings in Mississippi and across the Gulf Coast.
Author(s)
University of Florida IFAS Extension
Organization(s)
University of Florida IFAS Extension
Publication Date
Description
Fact sheet describing impact-resistant window systems with specifics on Florida’s building codes.
Author(s)
U.S. Geological Survey
Organization(s)
USGS
Publication Date
Description
Website providing a probabilistic map of the expected number of damaging earthquakes around the U.S.
Author(s)
International Code Council,
Florida Building Commission
Organization(s)
ICC,
FBC
Publication Date
Description
Florida building code including all the amendments and additions by Florida for the wind-borne debris regions and the high-velocity hurricane zone.
Author(s)
Insurance Institute for Business & Home Safety
Organization(s)
IBHS
Publication Date
Description
Report summarizing the requirements for strenghtening and protecting the roof, openings in the house, and creating a continuous load path to strengthen walls and foundation per the IBHS Fortified Homes Hurricane Standard for New Homes.
*For non-dated media, such as websites, the date listed is the date accessed.
Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

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