Publication #ABE 377

Topics: Agricultural and Biological Engineering� |� Ruppert, Kathleen Carlton� |� Knowles, Harold S III� |� Lenfesty, Karla A� |�Haldeman, Barbara M� |�Education + Action = Wind Damage Mitigation series�

Reinforcing Your Roof¹

Hal S. Knowles, III, Kathleen C. Ruppert, Karla A. Lenfesty, and Barbara Haldeman²

The roof helps keep your home comfortable and dry. But during the high winds of a hurricane, poorly designed or maintained roofs can fail. Here are a few tips to reinforce your roof.

Figure 1.

Source: Institute for Business & Home Safety

Why Does Roof Design Matter?

Roofs with very steep slopes perform poorly against horizontal winds. Roofs with very shallow slopes allow increased vertical uplift. Slopes between 3:12 and 6:12 (horizontal run : vertical rise) are often considered the safest.

Both hip roofs and gable roofs are common throughout Florida. Because of their design, hip roofs are more resistant to high wind loads.

Gable roofs can be made safer with a few minor improvements.

Figure 2.

Cross (“X”) Brace the Gable (“A” Frame)

First, install diagonal cross bracing between the gable truss and the fourth truss back. Be safe, remember to “X” the “A”. (See the diagram at the bottom of the left-hand column.)

Brace to Avoid the Domino Effect

Second, install horizontal truss bracing to prevent the trusses from getting pushed together from extreme winds. This is shown in the photo on the left. Be safe, remember to “avoid the domino effect”.

Figure 3.

Third, install a shutter over any vents on the gable end wall. If you are building a new house with a gable roof, consider using continuous wall construction or balloon framing. This creates a solid unit of wall framing from the ground through to the roof on the gabled end of the house.

Create a Continuous Load Path

A house is a system of connected parts. If there is one weak link in the system, the whole house can be damaged. This is why it is important to create a continuous load path between the ground and the top of your house. This unifies the vertical structure of your house and resists the uplift forces of hurricane winds.

A continuous load path requires that you anchor the house roof to the walls, the second floor to the first floor, and the walls to the foundation. This can be done using hurricane straps for the roof-to-wall and floor-to-floor connections, and anchor bolts for the wall-to-foundation connections.

Figure 4.

There are many hurricane straps and other anchoring devices available. Be sure to choose a product approved for use by the Miami-Dade County Building Code. Always use the manufacturer’s specifications for installation.

Proper Sheathing & Shingle Attachment

When installed improperly or with substandard materials, roof shingles, siding, and other exterior materials can be torn from a house. This allows wind and water inside, damaging the house. Also, these materials can become dangerous flying—or “wind-borne”—debris during a storm. Proper fastening techniques can prevent materials from being torn off a home during severe storms.

Connect roof sheathing to the roof framing with ten-penny weight common or eight-penny weight ring shank nails. Space them four inches apart along the edges, and six inches apart in the middle, of the plywood sheathing. Use wood adhesive underneath the sheathing along the connecting joint with the roof trusses.

Ring shank nails provide increased holding power as a result of their threaded rings. These rings bite into the sheathing and framing and resist higher uplift forces.

Figure 5.

Other Resources

Federal Alliance for Safe Homes

http://www.flash.org

Federal Emergency Management Agency | Disaster Prevention & Preparation Library

http://www.fema.gov/library

Florida Division of Emergency Management | Information Page

http://www.floridadisaster.org

Institute for Business and Home Safety

http://www.ibhs.org

University of Florida | Disaster Handbook

http://disaster.ifas.ufl.edu/

Footnotes

This document ABE 377 is Part 4 of 5 in the Education + Action = Wind Damage Mitigation series. Publication date: November 2005.

Hal S. Knowles, III, Coordinator, Program for Resource Efficient Communities; Kathleen C. Ruppert, Associate Extension Scientist, Florida Energy Extension Service; Karla A. Lenfesty, Windstorm Damage Mitigation Program Specialist, St. Lucie County Cooperative Extension, Institute of Food and Agricultural Sciences, University of Florida; Barbara Haldeman, Editorial Assistant, Florida Energy Extension Service.

Publication partially funded from a Florida Department of Community Affairs Residential Construction Mitigation Program Grant.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

Reinforcing Your Roof1