Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 23 - Wood
Section 2304 - GENERAL CONSTRUCTION REQUIREMENTS
Subsection 2304.7 - Floor and roof sheathing
Current through Register 1531, September 27, 2024
TABLE 2304.7(1) ALLOWABLE SPANS FOR LUMBER FLOOR AND ROOF SHEATHINGa, b
| SPAN (inches) | MINIMUM NET THICKNESS (inches) OF LUMBER PLACED | |||
| Perpendicular to supports | Diagonally to supports | |||
| Surfaced dryc | Surfaced unseasoned | Surfaced dryc | Surfaced unseasoned | |
| Floors | ||||
| 24 | 3/4 | 25/32 | 3/4 | 25/32 |
| 16 | 5/8 | 11/16 | 5/8 | 11/16 |
| Roofs | ||||
| 24 | 5/8 | 11/16 | 3/4 | 25/32 |
| For SI: 1 inch = 25.4 mm. a. Installation details shall conform to Sections 2304.7.1 and 2304.7.2 for floor and roof sheathing, respectively. b. Floor or roof sheathing conforming with this table shall be deemed to meet the design criteria of Section 2304.7. c. Maximum 19-percent moisture content. |
TABLE 2304.7(2) SHEATHING LUMBER, MINIMUM GRADE REQUIREMENTS: BOARD GRADE
| SOLID FLOOR OR ROOF SHEATHING | SPACED ROOF SHEATHING | GRADING RULES |
| Utility | Standard | NLGA, WCLIB, WWPA |
| 4 common or utility | 3 common or standard | NLGA, WCLIB, WWPA, NSLB or NELMA |
| No. 3 | No. 2 | SPIB |
| Merchantable | Construction common | RIS |
TABLE 2304.7(3) ALLOWABLE SPANS AND LOADS FOR WOOD STRUCTURAL PANEL SHEATHING AND SINGLE-FLOOR GRADES CONTINUOUS OVER TWO OR MORE SPANS WITH STRENGTH AXIS PERPENDICULAR TO SUPPORTSa, b
| SHEATHING GRADES | ROOFc | FLOORd | ||||
| Panel span rating roof/floor span | Panel thickness (inches) | Maximum span (inches) | Loade (psf) | Maximum span (inches) | ||
| With edge supportf | Without edge support | Total load | Live load | |||
| 16/0 | 3/8 | 16 | 16 | 40 | 30 | 0 |
| 20/0 | 3/8 | 20 | 20 | 40 | 30 | 0 |
| 24/0 | 3/8,7/16,1/ 2 | 24 | 20g | 40 | 30 | 0 |
| 24/16 | 7/16, 1/2 | 24 | 24 | 50 | 40 | 16 |
| 32/16 | 15/32,1/2,5/ 8 | 32 | 28 | 40 | 30 | 16h |
| 40/20 | 19/32,5/8,3/ 4,7/8 | 40 | 32 | 40 | 30 | 20h,i |
| 48/24 | 23/32,3/4,7/ 8 | 48 | 36 | 45 | 35 | 24 |
| 54/32 | 7/8, 1 | 54 | 40 | 45 | 35 | 32 |
| 60/32 | 7/8, 11/8 | 60 | 48 | 45 | 35 | 32 |
| SINGLE FLOOR GRADES | ROOFc | FLOORd | ||||
| Panel span rating | Panel thickness (inches) | Maximum span (inches) | Loade(psf) | Maximum span (inches) | ||
| With edge supportf | Without edge support | Total load | Live load | |||
| 16 o.c. | 1/2,19/32,5/ 8 | 24 | 24 | 50 | 40 | 16h |
| 20 o.c. | 19/32,5/8,3/ 4 | 32 | 32 | 40 | 30 | 20h,i |
| 24 o.c. | 23/32,3/4 | 48 | 36 | 35 | 25 | 24 |
| 32 o.c. | 7/8, 1 | 48 | 40 | 50 | 40 | 32 |
| 48 o.c. | 13/32, 11/8 | 60 | 48 | 50 | 40 | 48 |
| For SI: 1 inch = 25.4 mm, 1 pound per square foot =
0.0479 kN/m2. a. Applies to panels 24 inches or wider. b. Floor and roof sheathing conforming with this table shall be deemed to meet the design criteria of Section 2304.7. c. Uniform load deflection limitations 1/180 of span under live load plus dead load, 1/240 under live load only. d. Panel edges shall have approved tongue-and-groove joints or shall be supported with blocking unless 1/4-inch minimum thickness underlayment or 11/2 inches of approved cellular or lightweight concrete is placed over the subfloor, or finish floor is 3/4-inch wood strip. Allowable uniform load based on deflection of 1/360 of span is 100 pounds per square foot except the span rating of 48 inches on center is based on a total load of 65 pounds per square foot. e. Allowable load at maximum span. f. Tongue-and-groove edges, panel edge clips (one midway between each support, except two equally spaced between supports 48 inches on center), lumber blocking or other. Only lumber blocking shall satisfy blocked diaphragm requirements. g. For 1/2-inch panel, maximum span shall be 24 inches. h. Span is permitted to be 24 inches on center where 3/4-inch wood strip flooring is installed at right angles to joist. i. Span is permitted to be 24 inches on center for floors where 11/2 inches of cellular or lightweight concrete is applied over the panels. |
TABLE 2304.7(4) ALLOWABLE SPAN FOR WOOD STRUCTURAL PANEL COMBINATION SUBFLOOR-UNDERLAYMENT (SINGLE FLOOR)a, b (Panels Continuous Over Two or More Spans and Strength Axis Perpendicular to Supports)
| IDENTIFICATION | MAXIMUM SPACING OF JOISTS (inches) | ||||
| 16 | 20 | 24 | 32 | 48 | |
| Species groupc | Thickness (inches) | ||||
| 1 | 1/2 | 5/8 | 3/4 | - | - |
| 2, 3 | 5/8 | 3/4 | 7/8 | - | - |
| 4 | 3/4 | 7/8 | 1 | - | - |
| Single floor span ratingd | 16 o.c. | 20 o.c. | 24 o.c. | 32 o.c. | 48 o.c. |
| For SI: 1 inch = 25.4 mm, 1 pound per square foot =
0.0479 kN/m2. a. Spans limited to value shown because of possible effects of concentrated loads. Allowable uniform loads based on deflection of 1/360 of span is 100 pounds per square foot except allowable total uniform load for 11/8-inch wood structural panels over joists spaced 48 inches on center is 65 pounds per square foot. Panel edges shall have approved tongue-and-groove joints or shall be supported with blocking, unless 1/4-inch minimum thickness underlayment or 11/2 inches of approved cellular or lightweight concrete is placed over the subfloor, or finish floor is 3/4-inch wood strip. b. Floor panels conforming with this table shall be deemed to meet the design criteria of Section 2304.7. c. Applicable to all grades of sanded exterior-type plywood. See DOC PS 1 for plywood species groups. d. Applicable to Underlayment grade, C-C (Plugged) plywood, and Single Floor grade wood structural panels. |
TABLE 2304.7(5) ALLOWABLE LOAD (PSF) FOR WOOD STRUCTURAL PANEL ROOF SHEATHING CONTINUOUS OVER TWO OR MORE SPANS AND STRENGTH AXIS PARALLEL TO SUPPORTS (Plywood Structural Panels Are Five-Ply, Five-Layer Unless Otherwise Noted)a, b
| PANEL GRADE | THICKNESS (inch) | MAXIMUM SPAN (inches) | LOAD AT MAXIMUM SPAN (psf) | |
| Live | Total | |||
| Structural I sheathing | 7/16 | 24 | 20 | 30 |
| 15/32 | 24 | 35c | 45c | |
| 1/2 | 24 | 40c | 50c | |
| 19/32,5/8 | 24 | 70 | 80 | |
| 23/32,3/4 | 24 | 90 | 100 | |
| Sheathing, other grades covered in DOC PS 1 or DOC PS 2 | 7/16 | 16 | 40 | 50 |
| 15/32 | 24 | 20 | 25 | |
| 1/2 | 24 | 25 | 30 | |
| 19/32 | 24 | 40c | 50c | |
| 5/8 | 24 | 45c | 55c | |
| 23/32,3/4 | 24 | 60c | 65c | |
| For SI: 1 inch = 25.4 mm, 1 pound per square foot =
0.0479 kN/m2. a. Roof sheathing conforming with this table shall be deemed to meet the design criteria of Section 2304.7. b. Uniform load deflection limitations 1/180 of span under live load plus dead load, 1/240 under live load only. Edges shall be blocked with lumber or other approved type of edge supports. c. For composite and four-ply plywood structural panel, load shall be reduced by 15 pounds per square foot. |
2304.7.1 Structural floor sheathing. Structural floor sheathing shall be designed in accordance with the general provisions of this code and the special provisions in this section.
Floor sheathing conforming to the provisions of Table 2304.7(1), 2304.7(2), 2304.7(3) or 2304.7(4) shall be deemed to meet the requirements of this section.
2304.7.2 Structural roof sheathing. Structural roof sheathing shall be designed in accordance with the general provisions of this code and the special provisions in this section.
Roof sheathing conforming to the provisions of Table 2304.7(1), 2304.7(2), 2304.7(3) or 2304.7(5) shall be deemed to meet the requirements of this section. Wood structural panel roof sheathing shall be bonded by exterior glue.
