Code of Massachusetts Regulations › 780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS › Chapter 6 - Types of Construction › Section 602 - CONSTRUCTION CLASSIFICATION › Subsection 602.4 - Type IV

Current through Register 1525, July 5, 2024
Type IV construction (Heavy Timber, HT) is that type of
				  construction in which the exterior walls are of noncombustible materials and
				  the interior building elements are of solid or laminated wood without concealed
				  spaces. The details of Type IV construction shall comply with the provisions of
				  this section.
Fire-retardant-treated wood
framing complying
				  with Section 2303.2 shall be permitted within exterior wall assemblies with a
				  2-hour rating or less. Minimum solid sawn nominal dimensions are required for
				  structures built using Type IV construction (HT). For glued-laminated members
				  the equivalent net finished width and depths corresponding to the minimum
				  nominal width and depths of solid sawn lumber are required as specified in
				  Table 602.4.
TABLE 602.4 WOOD MEMBER SIZE
MINIMUM NOMINAL SOLID SAWN
							 SIZE
MINIMUM GLUED-LAMINATED NET
							 SIZE
Width, inch
Depth, inch
Width, inch
Depth, inch
8
8
6 3/4
8 1/4
6
10
5
10 1/2
6
8
5
8 1/4
6
6
5
6
4
6
3
6 7/8
For SI: 1 inch = 25.4 mm.
602.4.1
Columns.
Wood columns shall be sawn or glued laminated and shall
				not be less than 8 inches (203 mm), nominal, in any dimension where supporting
				floor loads and not less than 6 inches (152 mm) nominal in width and not less
				than 8 inches (203 mm) nominal in depth where supporting roof and ceiling loads
				only. Columns shall be continuous or superimposed and connected in an
approved
manner.
602.4.2
Floor framing.
Wood
				beams and girders shall be of sawn or glued-laminated timber and shall be not
				less than 6 inches (152 mm) nominal in width and not less than 10 inches (254
				mm) nominal in depth. Framed sawn or glued-laminated timber arches, which
				spring from the floor line and support floor loads, shall be not less than 8
				inches (203 mm) nominal in any dimension. Framed timber trusses supporting
				floor loads shall have members of not less than 8 inches (203 mm) nominal in
				any dimension.
602.4.3
Roof
				framing.
Wood-frame or glued-laminated arches for roof construction,
				which spring from the floor line or from grade and do not support floor loads,
				shall have members not less than 6 inches (152 mm) nominal in width and have
				not less than 8 inches (203 mm) nominal in depth for the lower half of the
				height and not less than 6 inches (152 mm) nominal in depth for the upper half.
				Framed or glued-laminated arches for roof construction that spring from the top
				of walls or wall abutments, framed timber trusses and other roof framing, which
				do not support floor loads, shall have members not less than 4 inches (102 mm)
				nominal in width and not less than 6 inches (152 mm) nominal in depth. Spaced
				members shall be permitted to be composed of two or more pieces not less than 3
				inches (76 mm) nominal in thickness where blocked solidly throughout their
				intervening spaces or where spaces are tightly closed by a continuous wood
				cover plate of not less than 2 inches (51 mm) nominal in thickness secured to
				the underside of the members. Splice plates shall be not less than 3 inches (76
				mm) nominal in thickness. Where protected by
approved
automatic sprinklers under the roof deck, framing members shall be not less
				than 3 inches (76 mm) nominal in width.
602.4.4
Floors.
Floors shall be
				without concealed spaces. Wood floors shall be of sawn or glued-laminated
				planks, splined or tongue-and-groove, of not less than 3 inches (76 mm) nominal
				in thickness covered with 1-inch (25 mm) nominal dimension tongue-and-groove
				flooring, laid crosswise or diagonally, or 0.5-inch (12.7 mm) particleboard or
				planks not less than 4 inches (102 mm) nominal in width set on edge close
				together and well spiked and covered with 1-inch (25 mm) nominal dimension
				flooring or 15/32-inch (12
				mm) wood structural panel or 0.5-inch (12.7 mm) particleboard. The lumber shall
				be laid so that no continuous line of joints will occur except at points of
				support. Floors shall not extend closer than 0.5 inch (12.7 mm) to walls. Such
				0.5-inch (12.7 mm) space shall be covered by a molding fastened to the wall and
				so arranged that it will not obstruct the swelling or shrinkage movements of
				the floor. Corbeling of masonry walls under the floor shall be permitted to be
				used in place of molding.
602.4.5
Roofs.
Roofs shall be without concealed spaces and wood roof
				decks shall be sawn or glued laminated, splined or tongue-and-groove plank, not
				less than 2 inches (51 mm) nominal in thickness,
				11/8-inch-thick (32 mm) wood
				structural panel (exterior glue), or of planks not less than 3 inches (76 mm)
				nominal in width, set on edge close together and laid as required for floors.
				Other types of decking shall be permitted to be used if providing equivalent
fire resistance
and structural properties.
602.4.6
Partitions.
Partitions
				shall be of solid wood construction formed by not less than two layers of
				1-inch (25 mm) matched boards or laminated construction 4 inches (102 mm)
				thick, or of 1-hour fire-resistance-rated construction.
602.4.7
Exterior structural
				members.
Where a horizontal separation of 20 feet (6096 mm) or more is
				provided, wood columns and arches conforming to heavy timber sizes shall be
				permitted to be used externally.