Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 23 - Wood
Section 2308 - CONVENTIONAL LIGHT-FRAME CONSTRUCTION
Subsection 2308.8 - Floor joists

Universal Citation: 780 CMR MA Code of Regs 2308.8

Current through Register 1531, September 27, 2024

Spans for floor joists shall be in accordance with Table 2308.8(1) or 2308.8(2). For other grades and or species, refer to the AF & PA Span Tables for Joists and Rafters.

2308.8.1 Bearing. Except where supported on a 1-inch by 4-inch (25.4 mm by 102 mm) ribbon strip and nailed to the adjoining stud, the ends of each joist shall not have less than 11/2 inches (38 mm) of bearing on wood or metal, or less than 3 inches (76 mm) on masonry.

TABLE 2308.8(1) FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential Sleeping Areas, Live Load = 30 pounds per square foot, L/[Delta] = 360)

JOIST SPACING (inches) SPECIES AND GRADE DEAD LOAD = 10 psf DEAD LOAD = 20 psf
2 x 6 2 x 8 2 x 10 2 x 12 2 x 6 2 x 8 2 x 10 2 x 12
Maximum floor joist spans
(ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.)
12 Douglas Fir-Larch SS 12-6 16-6 21-0 25-7 12-6 16-6 21-0 25-7
Douglas Fir-Larch #1 12-0 15-10 20-3 24-8 12-0 15-7 19-0 22-0
Douglas Fir-Larch #2 11-10 15-7 19-10 23-0 11-6 14-7 17-9 20-7
Douglas Fir-Larch #3 9-8 12-4 15-0 17-5 8-8 11-0 13-5 15-7
Hem-Fir SS 11-10 15-7 19-10 24-2 11-10 15-7 19-10 24-2
Hem-Fir #1 11-7 15-3 19-5 23-7 11-7 15-2 18-6 21-6
Hem-Fir #2 11-0 14-6 18-6 22-6 11-0 14-4 17-6 20-4
Hem-Fir #3 9-8 12-4 15-0 17-5 8-8 11-0 13-5 15-7
Southern Pine SS 12-3 16-2 20-8 25-1 12-3 16-2 20-8 25-1
Southern Pine #1 12-0 15-10 20-3 24-8 12-0 15-10 20-3 24-8
Southern Pine #2 11-10 15-7 19-10 24-2 11-10 15-7 18-7 21-9
Southern Pine #3 10-5 13-3 15-8 18-8 9-4 11-11 14-0 16-8
Spruce-Pine-Fir SS 11-7 15-3 19-5 23-7 11-7 15-3 19-5 23-7
Spruce-Pine-Fir #1 11-3 14-11 19-0 23-0 11-3 14-7 17-9 20-7
Spruce-Pine-Fir #2 11-3 14-11 19-0 23-0 11-3 14-7 17-9 20-7
Spruce-Pine-Fir #3 9-8 12-4 15-0 17-5 8-8 11-0 13-5 15-7
16 Douglas Fir-Larch SS 11-4 15-0 19-1 23-3 11-4 15-0 19-1 23-0
Douglas Fir-Larch #1 10-11 14-5 18-5 21-4 10-8 13-6 16-5 19-1
Douglas Fir-Larch #2 10-9 14-1 17-2 19-11 9-11 12-7 15-5 17-10
Douglas Fir-Larch #3 8-5 10-8 13-0 15-1 7-6 9-6 11-8 13-6
Hem-Fir SS 10-9 14-2 18-0 21-11 10-9 14-2 18-0 21-11
Hem-Fir #1 10-6 13-10 17-8 20-9 10-4 13-1 16-0 18-7
Hem-Fir #2 10-0 13-2 16-10 19-8 9-10 12-5 15-2 17-7
Hem-Fir #3 8-5 10-8 13-0 15-1 7-6 9-6 11-8 13-6
Southern Pine SS 11-2 14-8 18-9 22-10 11-2 14-8 18-9 22-10
Southern Pine #1 10-11 14-5 18-5 22-5 10-11 14-5 17-11 21-4
Southern Pine #2 10-9 14-2 18-0 21-1 10-5 13-6 16-1 18-10
Southern Pine #3 9-0 11-6 13-7 16-2 8-1 10-3 12-2 14-6
Spruce-Pine-Fir SS 10-6 13-10 17-8 21-6 10-6 13-10 17-8 21-4
Spruce-Pine-Fir #1 10-3 13-6 17-2 19-11 9-11 12-7 15-5 17-10
Spruce-Pine-Fir #2 10-3 13-6 17-2 19-11 9-11 12-7 15-5 17-10
Spruce-Pine-Fir #3 8-5 10-8 13-0 15-1 7-6 9-6 11-8 13-6

TABLE 2308.8(1)-continued FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential Sleeping Areas, Live Load = 30 pounds per square foot, L/[Delta] = 360)

JOIST SPACING (inches) SPECIES AND GRADE DEAD LOAD = 10 psf DEAD LOAD = 20 psf
2 x 6 2 x 8 2 x 10 2 x 12 2 x 6 2 x 8 2 x 10 2 x 12
Maximum floor joist spans
(ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.)
19.2 Douglas Fir-Larch SS 10-8 14-1 18-0 21-10 10-8 14-1 18-0 21-0
Douglas Fir-Larch #1 10-4 13-7 16-9 19-6 9-8 12-4 15-0 17-5
Douglas Fir-Larch #2 10-1 12-10 15-8 18-3 9-1 11-6 14-1 16-3
Douglas Fir-Larch #3 7-8 9-9 11-10 13-9 6-10 8-8 10-7 12-4
Hem-Fir SS 10-1 13-4 17-0 20-8 10-1 13-4 17-0 20-7
Hem-Fir #1 9-10 13-0 16-4 19-0 9-6 12-0 14-8 17-0
Hem-Fir #2 9-5 12-5 15-6 17-1 8-11 11-4 13-10 16-1
Hem-Fir #3 7-8 9-9 11-10 13-9 6-10 8-8 10-7 12-4
Southern Pine SS 10-6 13-10 17-8 21-6 10-6 13-10 17-8 21-6
Southern Pine #1 10-4 13-7 17-4 21-1 10-4 13-7 16-4 19-6
Southern Pine #2 10-1 13-4 16-5 19-3 9-6 12-4 14-8 17-2
Southern Pine #3 8-3 10-6 12-5 14-9 7-4 9-5 11-1 13-2
Spruce-Pine-Fir SS 9-10 13-0 16-7 20-2 9-10 13-0 16-7 19-6
Spruce-Pine-Fir #1 9-8 12-9 15-8 18-3 9-1 11-6 14-1 16-3
Spruce-Pine-Fir #2 9-8 12-9 15-8 18-3 9-1 11-6 14-1 16-3
Spruce-Pine-Fir #3 7-8 9-9 11-10 13-9 6-10 8-8 10-7 12-4
24 Douglas Fir-Larch SS 9-11 13-1 16-8 20-3 9-11 13-1 16-2 18-9
Douglas Fir-Larch #1 9-7 12-4 15-0 17-5 8-8 11-0 13-5 15-7
Douglas Fir-Larch #2 9-1 11-6 14-1 16-3 8-1 10-3 12-7 14-7
Douglas Fir-Larch #3 6-10 8-8 10-7 12-4 6-2 7-9 9-6 11-0
Hem-Fir SS 9-4 12-4 15-9 19-2 9-4 12-4 15-9 18-5
Hem-Fir #1 9-2 12-0 14-8 17-0 8-6 10-9 13-1 15-2
Hem-Fir #2 8-9 11-4 13-10 16-1 8-0 10-2 12-5 14-4
Hem-Fir #3 6-10 8-8 10-7 12-4 6-2 7-9 9-6 11-0
Southern Pine SS 9-9 12-10 16-5 19-11 9-9 12-10 16-5 19-11
Southern Pine #1 9-7 12-7 16-1 19-6 9-7 12-4 14-7 17-5
Southern Pine #2 9-4 12-4 14-8 17-2 8-6 11-0 13-1 15-5
Southern Pine #3 7-4 9-5 11-1 13-2 6-7 8-5 9-11 11-10
Spruce-Pine-Fir SS 9-2 12-1 15-5 18-9 9-2 12-1 15-0 17-5
Spruce-Pine-Fir #1 8-11 11-6 14-1 16-3 8-1 10-3 12-7 14-7
Spruce-Pine-Fir #2 8-11 11-6 14-1 16-3 8-1 10-3 12-7 14-7
Spruce-Pine-Fir #3 6-10 8-8 10-7 12-4 6-2 7-9 9-6 11-0

Check sources for availability of lumber in lengths greater than 20 feet.
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 47.8 N/m2.

TABLE 2308.8(2) FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential Living Areas, Live Load = 40 pounds per square foot, L/[Delta] = 360)

JOIST SPACING (inches) SPECIES AND GRADE DEAD LOAD = 10 psf DEAD LOAD = 20 psf
2 x 6 2 x 8 2 x 10 2 x 12 2 x 6 2 x 8 2 x 10 2 x 12
Maximum floor joist spans
(ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.)
12 Douglas Fir-Larch SS 11-4 15-0 19-1 23-3 11-4 15-0 19-1 23-3
Douglas Fir-Larch #1 10-11 14-5 18-5 22-0 10-11 14-2 17-4 20-1
Douglas Fir-Larch #2 10-9 14-2 17-9 20-7 10-6 13-3 16-3 18-10
Douglas Fir-Larch #3 8-8 11-0 13-5 15-7 7-11 10-0 12-3 14-3
Hem-Fir SS 10-9 14-2 18-0 21-11 10-9 14-2 18-0 21-11
Hem-Fir #1 10-6 13-10 17-8 21-6 10-6 13-10 16-11 19-7
Hem-Fir #2 10-0 13-2 16-10 20-4 10-0 13-1 16-0 18-6
Hem-Fir #3 8-8 11-0 13-5 15-7 7-11 10-0 12-3 14-3
Southern Pine SS 11-2 14-8 18-9 22-10 11-2 14-8 18-9 22-10
Southern Pine #1 10-11 14-5 18-5 22-5 10-11 14-5 18-5 22-5
Southern Pine #2 10-9 14-2 18-0 21-9 10-9 14-2 16-11 19-10
Southern Pine #3 9-4 11-11 14-0 16-8 8-6 10-10 12-10 15-3
Spruce-Pine-Fir SS 10-6 13-10 17-8 21-6 10-6 13-10 17-8 21-6
Spruce-Pine-Fir #1 10-3 13-6 17-3 20-7 10-3 13-3 16-3 18-10
Spruce-Pine-Fir #2 10-3 13-6 17-3 20-7 10-3 13-3 16-3 18-10
Spruce-Pine-Fir #3 8-8 11-0 13-5 15-7 7-11 10-0 12-3 14-3
16 Douglas Fir-Larch SS 10-4 13-7 17-4 21-1 10-4 13-7 17-4 21-0
Douglas Fir-Larch #1 9-11 13-1 16-5 19-1 9-8 12-4 15-0 17-5
Douglas Fir-Larch #2 9-9 12-7 15-5 17-10 9-1 11-6 14-1 16-3
Douglas Fir-Larch #3 7-6 9-6 11-8 13-6 6-10 8-8 10-7 12-4
Hem-Fir SS 9-9 12-10 16-5 19-11 9-9 12-10 16-5 19-11
Hem-Fir #1 9-6 12-7 16-0 18-7 9-6 12-0 14-8 17-0
Hem-Fir #2 9-1 12-0 15-2 17-7 8-11 11-4 13-10 16-1
Hem-Fir #3 7-6 9-6 11-8 13-6 6-10 8-8 10-7 12-4
Southern Pine SS 10-2 13-4 17-0 20-9 10-2 13-4 17-0 20-9
Southern Pine #1 9-11 13-1 16-9 20-4 9-11 13-1 16-4 19-6
Southern Pine #2 9-9 12-10 16-1 18-10 9-6 12-4 14-8 17-2
Southern Pine #3 8-1 10-3 12-2 14-6 7-4 9-5 11-1 13-2
Spruce-Pine-Fir SS 9-6 12-7 16-0 19-6 9-6 12-7 16-0 19-6
Spruce-Pine-Fir #1 9-4 12-3 15-5 17-10 9-1 11-6 14-1 16-3
Spruce-Pine-Fir #2 9-4 12-3 15-5 17-10 9-1 11-6 14-1 16-3
Spruce-Pine-Fir #3 7-6 9-6 11-8 13-6 6-10 8-8 10-7 12-4

TABLE 2308.8(2)-continued FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential Living Areas, Live Load = 40 pounds per square foot, L/[Delta] = 360)

JOIST SPACING (inches) SPECIES AND GRADE DEAD LOAD = 10 psf DEAD LOAD = 20 psf
2 x 6 2 x 8 2 x 10 2 x 12 2 x 6 2 x 8 2 x 10 2 x 12
Maximum floor joist spans
(ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.) (ft. - in.)
19.2 Douglas Fir-Larch SS 9-8 12-10 16-4 19-10 9-8 12-10 16-4 19-2
Douglas Fir-Larch #1 9-4 12-4 15-0 17-5 8-10 11-3 13-8 15-11
Douglas Fir-Larch #2 9-1 11-6 14-1 16-3 8-3 10-6 12-10 14-10
Douglas Fir-Larch #3 6-10 8-8 10-7 12-4 6-3 7-11 9-8 11-3
Hem-Fir SS 9-2 12-1 15-5 18-9 9-2 12-1 15-5 18-9
Hem-Fir #1 9-0 11-10 14-8 17-0 8-8 10-11 13-4 15-6
Hem-Fir #2 8-7 11-3 13-10 16-1 8-2 10-4 12-8 14-8
Hem-Fir #3 6-10 8-8 10-7 12-4 6-3 7-11 9-8 11-3
Southern Pine SS 9-6 12-7 16-0 19-6 9-6 12-7 16-0 19-6
Southern Pine #1 9-4 12-4 15-9 19-2 9-4 12-4 14-11 17-9
Southern Pine #2 9-2 12 -1 14-8 17-2 8-8 11-3 13-5 15-8
Southern Pine #3 7-4 9-5 11-1 13-2 6-9 8-7 10-1 12-1
Spruce-Pine-Fir SS 9-0 11-10 15-1 18-4 9-0 11-10 15-1 17-9
Spruce-Pine-Fir #1 8-9 11-6 14-1 16-3 8-3 10-6 12-10 14-10
Spruce-Pine-Fir #2 8-9 11-6 14-1 16-3 8-3 10-6 12-10 14-10
Spruce-Pine-Fir #3 6-10 8-8 10-7 12-4 6-3 7-11 9-8 11-3
24 Douglas Fir-Larch SS 9-0 11-11 15-2 18-5 9-0 11-11 14-9 17-1
Douglas Fir-Larch #1 8-8 11-0 13-5 15-7 7-11 10-0 12-3 14-3
Douglas Fir-Larch #2 8-1 10-3 12-7 14-7 7-5 9-5 11-6 13-4
Douglas Fir-Larch #3 6-2 7-9 9-6 11-0 5-7 7-1 8-8 10-1
Hem-Fir SS 8-6 11-3 14-4 17-5 8-6 11-3 14-4 16-10a
Hem-Fir #1 8-4 10-9 13-1 15-2 7-9 9-9 11-11 13-10
Hem-Fir #2 7-11 10-2 12-5 14-4 7-4 9-3 11-4 13-1
Hem-Fir #3 6-2 7-9 9-6 11-0 5-7 7-1 8-8 10-1
Southern Pine SS 8-10 11-8 14-11 18-1 8-10 11-8 14-11 18-1
Southern Pine #1 8-8 11-5 14-7 17-5 8-8 11-3 13-4 15-11
Southern Pine #2 8-6 11-0 13-1 15-5 7-9 10-0 12-0 14-0
Southern Pine #3 6-7 8-5 9-11 11-10 6-0 7-8 9-1 10-9
Spruce-Pine-Fir SS 8-4 11-0 14-0 17-0 8-4 11-0 13-8 15-11
Spruce-Pine-Fir #1 8-1 10-3 12-7 14-7 7-5 9-5 11-6 13-4
Spruce-Pine-Fir #2 8-1 10-3 12-7 14-7 7-5 9-5 11-6 13-4
Spruce-Pine-Fir #3 6-2 7-9 9-6 11-0 5-7 7-1 8-8 10-1

Check sources for availability of lumber in lengths greater than 20 feet.
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 47.8 N/m2.
a. End bearing length shall be increased to 2 inches.

2308.8.2 Framing details. Joists shall be supported laterally at the ends and at each support by solid blocking except where the ends of the joists are nailed to a header, band or rim joist or to an adjoining stud or by other means. Solid blocking shall not be less than 2 inches (51mm) in thickness and the full depth of the joist. Notches on the ends of joists shall not exceed one-fourth the joist depth. Holes bored in joists shall not be within 2 inches (51 mm) of the top or bottom of the joist, and the diameter of any such hole shall not exceed one-third the depth of the joist. Notches in the top or bottom of joists shall not exceed one-sixth the depth and shall not be located in the middle third of the span.

Joist framing from opposite sides of a beam, girder or partition shall be lapped at least 3 inches (76 mm) or the opposing joists shall be tied together in an approved manner.

Joists framing into the side of a wood girder shall be supported by framing anchors or on ledger strips not less than 2 inches by 2 inches (51 mm by 51 mm).

2308.8.2.1 Engineered wood products. Cuts, notches and holes bored in trusses, structural composite lumber, structural glue-laminated members or I-joists are not permitted except where permitted by the manufacturer's recommendations or where the effects of such alterations are specifically considered in the design of the member by a registered design professional.

2308.8.3 Framing around openings. Trimmer and header joists shall be doubled, or of lumber of equivalent cross section, where the span of the header exceeds 4 feet (1219 mm). The ends of header joists more than 6 feet (1829 mm) long shall be supported by framing anchors or joist hangers unless bearing on a beam, partition or wall. Tail joists over 12 feet (3658 mm) long shall be supported at the header by framing anchors or on ledger strips not less than 2 inches by 2 inches (51 mm by 51 mm).

2308.8.4 Supporting bearing partitions. Bearing partitions parallel to joists shall be supported on beams, girders, doubled joists, walls or other bearing partitions. Bearing partitions perpendicular to joists shall not be offset from supporting girders, walls or partitions more than the joist depth unless such joists are of sufficient size to carry the additional load.

2308.8.5 Lateral support. Floor, attic and roof framing with a nominal depth-to-thickness ratio greater than or equal to 5:1 shall have one edge held in line for the entire span. Where the nominal depth-to-thickness ratio of the framing member exceeds 6:1, there shall be one line of bridging for each 8 feet (2438 mm) of span, unless both edges of the member are held in line. The bridging shall consist of not less than 1-inch by 3-inch (25 mm by 76 mm) lumber, double nailed at each end, of equivalent metal bracing of equal rigidity, full-depth solid blocking or other approved means. A line of bridging shall also be required at supports where equivalent lateral support is not otherwise provided.

2308.8.6 Structural floor sheathing. Structural floor sheathing shall comply with the provisions of Section 2304.7.1.

2308.8.7 Under-floor ventilation. For under-floor ventilation, see Section 1203.3.

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