Roof Deck Material

Plywood/OSB - The most common roof deck types in residential construction today are plywood and Oriented Strand Board (OSB) decks.

Dimensional Lumber - Prior to the introduction of plywood to the construction industry (in the 1950's), the most common roof decking material was dimensional lumber or tongue and groove (T&G) decking. Dimensional lumber or T&G are usually 4- to 8-inch wide boards that are nominally 1-inch thick (3/4-inch actual thickness) and are laid in a fashion that is parallel to the ridge or diagonal to the ridge. Dimensional Lumber roof decks are not typically used in today's construction because of the higher labor costs.

Concrete - Concrete decks are roof structures composed of cast-in-place or pre-cast structural concrete designed to be self-supporting and integrally attached to the wall/support system. These types of systems typically get the largest credits from insurance companies.

Roof Deck Attachment

Dimensional lumber decks are typically stronger than plywood/OSB roof decks because they are attached with more nails than plywood/ OSB decks. Thus, even older homes built before the introduction of high-wind criteria into the local building codes may qualify for wind insurance credits.

The roof deck connection type can be determined on existing buildings by using a metal detector to locate the nails or screws. The following is the type of deck connections for which insurance companies may give credits.

The determination of roof deck attachment generally requires verification by a construction professional or other inspector authorized by the insurance company. The following items describe the typical roof deck attachment methods used in residential construction. Each of the nail options refers to the size of the nail (commonly referred to as a penny size (d)) and the spacing of nails along the framing members. The two numbers refer to the spacing along the edges of the plywood and the spacing of nails along the interior members of the plywood.

8d Nails @ 6/6 - Roof deck is attached with 8d (2.5" long) nails spaced at 6 inches on the edge of the sheathing and the interior of the sheathing. This connection pattern is seen mostly in newer homes built to high wind standards.

Screws/Bolts - Instead of using nails to attach the deck, some manufacturers are now producing screw guns that can install screws almost as fast as nails. Screws typically have must greater pullout resistance than equivalent lengths of nails.

8d Nails @ 6/12 - Roof deck is attached with 8d (2.5" long) nails spaced at 6 inches along the edge of the sheathing and 12 inches in the interior of the sheathing.

6d Nails @ 6/12 - Roof deck is attached with shorter 6d (2" long) nails spaced at 6 inches along the edge of the sheathing and 12 inches in the interior of the sheathing.