Tornadoes: Roof - Protecting Your Roof Deck
Material provided by Federal Alliance for Safe Homes http://www.flash.org/
The roof deck forms one of your home's critical shields of protection from high winds and rain. Unfortunately, if this shield is not fastened properly it may be lost during high winds.
While the loss of roof coverings can make your home vulnerable to water infiltration, loss of the roof's sheathing, often referred to as decking, can result in excessive damage to the structure of your home and your possessions.
As wind blows over the roof, uplift forces pull at the roof. These uplift forces try to pull off the roof covering and the roof deck. When the roof decking is blown off, the inside of your home becomes exposed to the elements. Trusses or rafters may become unstable and the entire roof may collapse.
The following techniques can be used during roof installation on both new and existing homes, and are best performed by a licensed, professional contractor:
- Install a roof deck of 5/8” thick solid plywood to maximize wind and windborne debris resistance with 10d or 8d ring shank nails spaced at 6 inches along the panel edges and every 6 inches in the field of the plywood panel. Make sure that the nails penetrate the decking directly into the roof framing.
- When re-roofing your existing home, be sure at the attachment of the roof deck to the roof framing and make sure the nails are spaced at 6” on center. If it’s not, add fasteners as described above to strengthen the attachment.
- Create a "sealed roof deck" secondary water barrier by installing self-adhering flashing tape or modified polymer bitumen strips, commonly called peel and seal, over the joints in your roof deck. This will help keep out the rain if the roof covering is damaged or destroyed by severe weather.
- Install one layer of #30 underlayment, sometimes called felt paper, over the roof decking and sealed roof deck. The felt helps with drainage in the event water gets under the roof covering.
- All nails used to attach the roof sheathing must penetrate the underlying roof trusses or rafters otherwise the sheathing will not be securely attached and can be more easily torn away by high winds. Inadequate attachment of roof sheathing, resulting from poor workmanship, has been a common cause of roof failures during tornadoes and other storms with high winds.
Finally, you can significantly increase the roof's sheathing resistance to uplift from the wind by applying a bead of construction adhesive using a caulking gun along both sides of the intersection of the roof decking and the rafters or trusses. Be sure to look for a premium, APA AFG-01 rated adhesive.
Benefits of Using This Mitigation Strategy
- Helps to prevent damage to a structure and its contents
- Helps to prevent injuries to occupants
Technical Information Provided by FEMA