Timber Decking

For glued-laminated decking, two or more pieces of lumber are laminated into a single decking member, usually with nominal thickness of 2, 3, or 4 in. Other thicknesses may also be available. There are no consensus standards for gluedlaminated decking. Decking manufacturers should be consulted for design information.
Solid-sawn decking usually is fabricated with edges tongued and grooved, shiplap, or groove cut for splines, to provide transfer of vertical load between pieces.
The decking may be end-matched, square end, or end-grooved for splines. As indicated in Fig. 10.22, the decking may be arranged in various patterns over supports.
In Type 1, the pieces are simply supported. Type 2 has a controlled random layup. Type 3 contains intermixed cantilevers. Type 4 consists of a combination of simple-span and two-span continuous pieces. Type 5 is two-span continuous.
In Types 1, 4, and 5, end joints bear on supports. For this reason, these types are recommended for thin decking, such as 2-in.
Type 3, with intermixed cantilevers, and Type 2, with controlled random layup, are used for deck continuous over three or more spans. These types permit some of the end joints to be located between supports. Hence, provision must be made for load transfer at those joints. Tongue-and-groove edges, wood splines on each edge of the course, horizontal spikes between courses, and end matching or metal end splines may be used to transfer shear and bending stresses.
In Type 2, the distance between end joints in adjacent courses should be at least 2 ft for 2-in deck and 4 ft for 3- and 4-in deck. Joints approximately lined up   (within 6 in of being in line) should be separated by at least two courses. All pieces should rest on at least one support, and not more than one end joint should fall between supports in each course.

In Type 3, every third course is simple span. Pieces in other courses cantilever over supports and end joints fall at alternate quarter or third points of the spans.

Each piece rests on at least one support.
To restrain laterally supporting members of 2-in deck in Types 2 and 3, the pieces in the first and second courses and in every seventh course should bear on at least two supports. End joints in the first course should not occur on the same supports as end joints in the second course unless some construction, such as plywood overlayment, provides continuity. Nail end distance should be sufficient to develop the lateral nail strength required.

Heavy-timber decking is laid with wide faces bearing on the supports. Each piece must be nailed to each support. For 2-in decking a 31⁄2-in (16d) toe and face nail should be used in each 6-in-wide piece at supports, with three nails for wider  pieces. Tongue-and-groove decking generally is also toenailed through the tongue.

For 3-in decking, each piece should be toenailed with one 4-in (20d) spike and face-nailed with one 5-in (40d) spike at each support. For 4-in decking, each piece should be toenailed at each support with one 5-in (40d) nail and face-nailed there with one 6-in (60d) spike.

Courses of 3- and 4-in double tongue-and-groove decking should be spiked to each other with 81⁄2-in spikes not more than 30 in apart. One spike should not be more than 10 in from each end of each piece. The spikes should be driven through predrilled holes. Two-inch decking is not fastened together horizontally with spikes.
Deck design usually is governed by maximum permissible deflection in end spans. But each design should be checked for bending stress. For load-span tables and more information on sawn lumber decking, refer to AITC 112, Standard for Heavy Timber Roof Decking, and AITC 118, Standard for 2-in Nominal Thickness Lumber Roof Decking for Structural Applications, American Institute of Timber Construction, Englewood, Colo.