Thunderstorms: 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, this shield is often the second to 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 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 shack common nails spaced at 4 inches along the panel edges and every six inches in the field of the plywood panel. Make sure that the nails penetrate the decking directly into the roof framing.
- In your existing home, be sure to look in the attic to confirm that the roof decking is properly nailed to the roof framing. If you can see nails along the sides of rafters or trusses where the nail penetrates the decking, your roof deck may not be securely attached.
- Create a 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 in the event 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 secondary water barrier. 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, 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 hurricanes and other storms with high winds.
Finally, you can significantly increase the roofs 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