Code of Massachusetts Regulations › 780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS › Chapter 23 - Wood › Section 2304 - GENERAL CONSTRUCTION REQUIREMENTS › Subsection 2304.8 - Lumber decking

Current through Register 1525, July 5, 2024
2304.8.1
General.
Lumber decking shall be designed and installed in accordance
				with the general provisions of this code and Section 2304.8. Each piece shall
				be square end trimmed. When random lengths are furnished, each piece shall be
				square end trimmed across the face so that at least 90 percent of the pieces
				are within 0.5 degrees (0.00873 rad) of square. The ends of the pieces shall be
				permitted to be beveled up to 2 degrees (0.0349 rad) from the vertical with the
				exposed face of the piece slightly longer than the opposite face of the piece.
				Tongue-and-groove decking shall be installed with the tongues up on sloped or
				pitched roofs with pattern faces down.
2304.8.2
Layup patterns.
Lumber
				decking is permitted to be laid up following one of five standard patterns as
				defined in Sections 2304.8.2.1 through 2304.8.2.5. Other patterns are permitted
				to be used provided they are substantiated through engineering analysis.
2304.8.2.1
Simple span pattern.
All pieces shall be supported on their ends (i.e., by two supports).
2304.8.2.2
Two-span continuous
				pattern.
All pieces shall be supported by three supports, and all end
				joints shall occur in line on alternating supports. Supporting members shall be
				designed to accommodate the load redistribution caused by this
				pattern.
2304.8.2.3
Combination simple and two-span continuous pattern.
Courses in end spans
				shall be alternating simple-span pattern and two-span continuous pattern. End
				joints shall be staggered in adjacent courses and shall bear on
				supports.
2304.8.2.4
Cantilevered pieces intermixed pattern.
The decking shall extend across
				a minimum of three spans. Pieces in each starter course and every third course
				shall be simple span pattern. Pieces in other courses shall be cantilevered
				over the supports with end joints at alternating quarter or third points of the
				spans. Each piece shall bear on at least one support.
2304.8.2.5
Controlled random
				pattern.
The decking shall extend across a minimum of three spans. End
				joints of pieces within 6 inches (152 mm) of the end joints of the adjacent
				pieces in either direction shall be separated by at least two intervening
				courses. In the end bays, each piece shall bear on at least one support. Where
				an end joint occurs in an end bay, the next piece in the same course shall
				continue over the first inner support for at least 24 inches (610 mm). The
				details of the controlled random pattern shall be as specified for each decking
				material in Section 2304.8.3.3, 2304.8.4.3 or 2304.8.5.3.
Decking that cantilevers beyond a support for a horizontal
				  distance greater than 18 inches (457 mm), 24 inches (610 mm) or 36 inches (914
				  mm) for 2-inch (51 mm), 3-inch (76 mm) and 4-inch (102 mm) nominal thickness
				  decking, respectively, shall comply with the following:
1. The maximum cantilevered length shall be
				30 percent of the length of the first adjacent interior span.
2. A structural fascia shall be fastened to
				each decking piece to maintain a continuous, straight line.
3. There shall be no end joints in the
				decking between the cantilevered end of the decking and the centerline of the
				first adjacent interior span.