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2308.7.3.1 Ceiling Joist and Rafter Connections

Building Code 2018 of Illinois > 23 Wood > 2308 Conventional Light-Frame Construction > 2308.7 Roof and Ceiling Framing > 2308.7.3 Ceiling Joist and Rafter Framing > 2308.7.3.1 Ceiling Joist and Rafter Connections

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Ceiling joists and rafters shall be nailed to each other and the assembly shall be nailed to the top wall plate in accordance with Tables 2304.10.1 and 2308.7.5. Ceiling joists shall be continuous or securely joined where they meet over interior partitions and be fastened to adjacent rafters in accordance with Tables 2304.10.1 and 2308.7.3.1 to provide a continuous rafter tie across the building where such joists are parallel to the rafters. Ceiling joists shall have a bearing surface of not less than 1¹/₂ inches (38 mm) on the top plate at each end.

Where ceiling joists are not parallel to rafters, an equivalent rafter tie shall be installed in a manner to provide a continuous tie across the building, at a spacing of not more than 4 feet (1219 mm) on center. The connections shall be in accordance with Tables 2308.7.3.1 and 2304.10.1, or connections of equivalent capacities shall be provided. Where ceiling joists or rafter ties are not provided at the top of the rafter support walls, the ridge formed by these rafters shall be supported by a girder conforming to Section 2308.8. Rafter ties shall be spaced not more than 4 feet (1219 mm) on center.

Rafter tie connections shall be based on the equivalent rafter spacing in Table 2308.7.3.1. Rafter-to-ceiling joist connections and rafter tie connections shall be of sufficient size and number to prevent splitting from nailing.

Roof framing member connection to braced wall lines shall be in accordance with Section 2308.6.7.2.

TABLE 2308.7.3.1

RAFTER TIE CONNECTIONS^g

RAFTER SLOPE	TIE SPACING (inches)	NO SNOW LOAD					GROUND SNOW LOAD (pound per square foot)
		NO SNOW LOAD					30 pounds per square foot				50 pounds per square foot
		Roof span (feet)
		12	20	28	36		12	20	28	36	12	20	28	36
		Required number of 16d common (3¹/₂^" x 0.162") nails^{a, b} per connection^{c, d, e, f}
3:12	12	4	6	8		10	4	6	8	11	5	8	12	15
	16	5	7	10		13	5	8	11	14	6	11	15	20
	24	7	11	15		19	7	11	16	21	9	16	23	30
	32	10	14	19		25	10	16	22	28	12	27	30	40
	48	14	21	29		37	14	32	36	42	18	32	46	60
4:12	12	3	4	5		6	3	5	6	8	4	6	9	11
	16	3	5	7		8	4	6	8	11	5	8	12	15
	24	4	7	10		12	5	9	12	16	7	12	17	22
	32	6	9	13		16	8	12	16	22	10	16	24	30
	48	8	14	19		24	10	18	24	32	14	24	34	44
5:12	12	3	3	4		5	3	4	5	7	3	5	7	9
	16	3	4	5		7	3	5	7	9	4	7	9	12
	24	4	6	8		10	4	7	10	13	6	10	14	18
	32	5	8	10		13	6	10	14	18	8	14	18	24
	48	7	11	15		20	8	14	20	26	12	20	28	36
7:12	12	3	3	3		4	3	3	4	5	3	4	5	7
	16	3	3	4		5	3	4	5	6	3	5	7	9
	24	3	4	6		7	3	5	7	9	4	7	10	13
	32	4	6	8		10	4	8	10	12	6	10	14	18
	48	5	8	11		14	6	10	14	18	9	14	20	26
9:12	12	3	3	3		3	3	3	3	4	3	3	4	5
	16	3	3	3		4	3	3	4	5	3	4	5	7
	24	3	3	5		6	3	4	6	7	3	6	8	10
	32	3	4	6		8	4	6	8	10	5	8	10	14
	48	4	6	9		11	5	8	12	14	7	12	16	20
12:12	12	3	3	3		3	3	3	3	3	3	3	3	4
	16	3	3	3		3	3	3	3	4	3	3	4	5
	24	3	3	3		4	3	3	4	6	3	4	6	8
	32	3	3	4		5	3	5	6	8	4	6	8	10
	48	3	4	6		7	4	7	8	12	6	8	12	16

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 47.8 N/m².

40d box (5" × 0.162") or 16d sinker (3¹/₄" × 0.148") nails are permitted to be substituted for 16d common (3¹/₂" × 0.16") nails.
Nailing requirements are permitted to be reduced 25 percent if nails are clinched.
Rafter tie heel joint connections are not required where the ridge is supported by a load-bearing wall, header or ridge beam.
Where intermediate support of the rafter is provided by vertical struts or purlins to a load-bearing wall, the tabulated heel joint connection requirements are permitted to be reduced proportionally to the reduction in span.
Equivalent nailing patterns are required for ceiling joist to ceiling joist lap splices.
Connected members shall be of sufficient size to prevent splitting due to nailing.
For snow loads less than 30 pounds per square foot, the required number of nails is permitted to be reduced by multiplying by the ratio of actual snow load plus 10 divided by 40, but not less than the number required for no snow load.

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