After unreinforced garage doors and unprotected sliding glass patio doors, gable ends are probably the most likely part of the building envelope to fail during a hurricane. In fact, insurance companies give policy premium discounts to homes that have no gable ends in the roof design. Since the active hurricane seasons of 2004 and 2005, many building industry representatives, including lumber and component manufacturers, building science consultants, homebuilders, even do-it-yourself homeowners, have been searching for cost-effective methods to strengthen gable ends. The FL Department of Community Affairs, through its Division of Emergency Management, Bureau of Mitigation, has compiled a list of recommended steps to reinforce gable ends as part of its extensive Hurricane Retrofit Guide series. To view the entire Hurricane Retrofit Guide series of recommendations for improvements that make homes more hurricane-resistant, write down the following web site and visit it after you complete this course:
Gable ends often fail at the top where they connect to the roof sheathing. Less frequently, gable ends fail at the bottom where they connect to the supporting wall below. In the worst case, the sheathing is sucked completely off the wall, the fasteners holding the gable end studs in place can fail, or the studs themselves can fail under the battering of the tropical storm winds. This results in the destruction of this entire triangular portion of the wall, allowing wind and rain into the space below the roof sheathing placing the entire structure at risk.
The first picture shows the most common type of gable end failure in which the fasteners attaching the sheathing to the top of the gable end truss have failed and the top of the truss has been sucked out of the opening.
source: FL Division of Emergency Management
The second picture shows a failure at the joint between the bottom of the gable end truss and the supporting wall. Surprisingly in this instance, the top joint held.
Gable ends are like sails and, during storms, they are subjected to positive pressures when the wind is blowing directly against them and negative or “suction” pressures when the wind is blowing from the opposite side of the house or from an angle. The taller the gable end, the more wind force it will experience.
source: FL Division of Emergency Management
There are 2 basic types of roof assemblies:
Site-built (“stick-built”) composed of ridge, rafters, ceiling joists, etc., or
Trusses.
The basic approach for both types of roof assemblies is to reinforce the gable ends at 3 points:
• By strengthening the connection at the top of the wall
• By strengthening the connection at the bottom of the wall
• And by reinforcing the sheathing and the studs that make up the wall itself.
All of the techniques for gable end reinforcement described in this course will be much easier to accomplish if the roof covering is ready to be replaced. During the process of re-roofing, sheathing above the gable ends can be removed revealing the underlying roof structure. The recommended framing improvements can be made and new sheathing can be installed with adhesive and nailed to current code specifications.
If the roof is not being replaced, the following techniques have to be carried out in the access area above the ceiling and below the roof sheathing. This can be extremely problematic. Getting to the work area from existing access points alone can be a challenge, and any work has to be carried out without damaging the finished ceiling below. Often there are obstructions to work around such as electrical wires, water lines, HVAC ducts, and recessed light fixtures to name just a few. Furthermore, any attic space with less than 3 feet of headroom is, for all practical purposes, inaccessible. Fortunately, the wind forces acting on gable ends are not a major concern until the height of the gable end at the peak is greater than 4 feet. Vaulted and cathedral ceilings present problems of their own which are discussed at the end of this course.
To continue with Module 4, please click Section 2.
