R804.3.1 Ceiling Joists

Cold-formed steel ceiling joists shall be in accordance with this section.

Ceiling joist size and thickness shall be determined in accordance with the limits set forth in Tables R804.3.1.1(1) and R804.3.1.1(2). When determining the size of ceiling joists, the lateral support of the top flange shall be classified as unbraced, braced at midspan or braced at third points in accordance with Section R804.3.1.3. Where sheathing material is attached to the top flange of ceiling joists or where the bracing is spaced closer than third point of the joists, the "third point" values from Tables R804.3.1.1(1) and R804.3.1.1(2) shall be used.

Ceiling joists shall have a bearing support length of not less than 1¹/₂ inches (38 mm) and shall be connected to roof rafters (heel joint) with No. 10 screws in accordance with Figure R804.3.1.1 and Table 804.3.1.1(3).

Where continuous joists are framed across interior bearing supports, the interior bearing supports shall be located within 24 inches (610 mm) of midspan of the ceiling joist, and the individual spans shall not exceed the applicable spans in Tables R804.3.1.1(1) and R804.3.1.1(2).

Where the attic is to be used as an occupied space, the ceiling joists shall be designed in accordance with Section R505.

TABLE R804.3.1.1(1) CEILING JOIST SPANS 10 PSF LIVE LOAD (NO ATTIC STORAGE)^{a, b, c}

MEMBER DESIGNATION	ALLOWABLE SPAN (feet - inches)
	Lateral Support of Top (Compression) Flange
	Unbraced		Midspan Bracing		Third-point Bracing
	Ceiling Joist Spacing (inches)
	16	24	16	24	16	24
350S162-33	9'-5″	8'-6″	12'-2″	10'-4″	12'-2″	10'-7″
350S162-43	10'-3″	9'-12″	13'-2″	11'-6″	13'-2″	11'-6″
350S162-54	11'-1″	9'-11″	13'-9″	12'-0″	13'-9″	12'-0″
350S162-68	12'-1″	10'-9″	14'-8″	12'-10″	14'-8″	12'-10″
550S162-33	10'-7″	9'-6″	14'-10″	12'-10″	15'-11″	13'-4″
550S162-43	11'-8″	10'-6″	16'-4″	14'-3″	17'-10″	15'-3″
550S162-54	12'-6″	11'-2″	17'-7″	15'-7″	19'-5″	16'-10″
550S162-68	13'-6″	12'-1″	19'-2″	17'-0″	21'-0″	18'-4″
800S162-33	‒	‒	‒	‒	‒	‒
800S162-43	13'-0″	11'-9″	18'-10″	17'-0″	21'-6″	19'-0″
800S162-54	13'-10″	12'-5″	20'-0″	18'-0″	22'-9″	20'-4″
800S162-68	14'-11″	13'-4″	21'-3″	19'-1″	24'-1″	21'-8″
1000S162-43	‒	‒	‒	‒	‒	‒
1000S162-54	14'-9″	13'-3″	21'-4″	19'-3″	24'-4″	22'-0″
1000S162-68	15'-10″	14'-2″	22'-8″	20'-5″	25'-9″	23'-2″
1200S162-43	‒	‒	‒	‒	‒	‒
1200S162-54	‒	‒	‒	‒	‒	‒
1200S162-68	16'-8″	14'-11″	23'-11″	21'-6″	27'-2″	24'-6″

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mil = 0.0254 mm, 1 pound per square foot = 0.0479 kPa.

a. Deflection criterion: L/240 for total loads.

b. Ceiling dead load = 5 psf.

c. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.

TABLE R804.3.1.1(2) CEILING JOIST SPANS 20 PSF LIVE LOAD (LIMITED ATTIC STORAGE)^{a, b, c}

MEMBER DESIGNATION	ALLOWABLE SPAN (feet - inches)
	Lateral Support of Top (Compression) Flange
	Unbraced		Midspan Bracing		Third-point Bracing
	Ceiling Joist Spacing (inches)
	16	24	16	24	16	24
350S162-33	8'-2″	6'-10″	9'-9″	6'-10″	9'-11″	6'-10″
350S162-43	8'-10″	7'-10″	11'-0″	9'-5″	11'-0″	9'-7″
350S162-54	9'-6″	8'-6″	11'-9″	10'-3″	11'-9″	10'-3″
350S162-68	10'-4″	9'-2″	12'-7″	11'-0″	12'-7″	11'-0″
550S162-33	9'-2″	8'-3″	12'-2″	8'-5″	12'-6″	8'-5″
550S162-43	10'-1″	9'-1″	13'-7″	11'-8″	14'-5″	12'-2″
550S162-54	10'-9″	9'-8″	14'-10″	12'-10″	15'-11″	13'-6″
550S162-68	11'-7″	10'-4″	16'-4″	14'-0″	17'-5″	14'-11″
800S162-33	‒	‒	‒	‒	‒	‒
800S162-43	11'-4″	10'-1″	16'-5″	13'-6″	18'-1″	13'-6″
800S162-54	20'-0″	10'-9″	17'-4″	15'-6″	19'-6″	27'-0″
800S162-68	12'-10″	11'-6″	18'-5″	16'-6″	20'-10″	18'-3″
1000S162-43	‒	‒	‒	‒	‒	‒
1000S162-54	12'-10″	11'-6″	18'-7″	16'-9″	21'-2″	15'-5″
1000S162-68	13'-8″	12'-3″	19'-8″	17'-8″	22'-4″	20'-1″
1200S162-43	‒	‒	‒	‒	‒	‒
1200S162-54	‒	‒	‒	‒	‒	‒
1200S162-68	14'-4″	12'-11″	20'-9″	18'-8″	23'-7″	21'-3″

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mil = 0.0254 mm, 1 pound per square foot = 0.0479 kPa.

a. Deflection criterion: L/240 for total loads.

b. Ceiling deal load = 5 psf.

c. Minimum Grade 33 ksi steel shall be used for 33 mil and 43 mil thicknesses. Minimum Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.

TABLE R804.3.1.1(3) NUMBER OF SCREWS REQUIRED FOR CEILING JOIST TO ROOF RAFTER CONNECTION^a

ROOF SLOPE	NUMBER OF SCREWS
	Building width (feet)
	24				28				32				36				40
	Ground snow load (psf)
	20	30	50	70	20	30	50	70	20	30	50	70	20	30	50	70	20	30	50	70
3/12	5	6	9	11	5	7	10	13	6	8	11	15	7	8	13	17	8	9	14	19
4/12	4	5	7	9	4	5	8	10	5	6	9	12	5	7	10	13	6	7	11	14
5/12	3	4	6	7	4	4	6	8	4	5	7	10	5	5	8	11	5	6	9	12
6/12	3	3	5	6	3	4	6	7	4	4	6	8	4	5	7	9	4	5	8	10
7/12	3	3	4	6	3	3	5	7	3	4	6	7	4	4	6	8	4	5	7	9
8/12	2	3	4	5	3	3	5	6	3	4	5	7	3	4	6	8	4	4	6	8
9/12	2	3	4	5	3	3	4	6	3	3	5	6	3	4	5	7	3	4	6	8
10/12	2	2	4	5	2	3	4	5	3	3	5	6	3	3	5	7	3	4	6	7
11/12	2	2	3	4	2	3	4	5	3	3	4	6	3	3	5	6	3	4	5	7
12/12	2	2	3	4	2	3	4	5	2	3	4	5	3	3	5	6	3	4	5	7

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479kPa.

a. Screws shall be No. 10.

FIGURE R804.3.1.1 JOIST TO RAFTER CONNECTION

The bottom flanges of ceiling joists shall be laterally braced by the application of gypsum board or continuous steel straps installed perpendicular to the joist run in accordance with one of the following:

1. Gypsum board shall be fastened with No. 6 screws in accordance with Section R702.

2. Steel straps with a minimum size of 1¹/₂ inches by 33 mils (38 mm by 0.84 mm) shall be installed at a maximum spacing of 4 feet (1219 mm). Straps shall be fastened to the bottom flange at each joist with one No. 8 screw and shall be fastened to blocking with two No. 8 screws. Blocking shall be installed between joists at a maximum spacing of 12 feet (3658 mm) measured along a line of continuous strapping (perpendicular to the joist run). Blocking shall also be located at the termination of all straps.

The top flanges of ceiling joists shall be laterally braced as required by Tables R804.3.1.1(1) and R804.3.1.1(2), in accordance with one of the following:

1. Minimum 33-mil (0.84 mm) C-shaped member in accordance with Figure R804.3.1.3(1).

2. Minimum 33-mil (0.84 mm) track section in accordance with Figure R804.3.1.3(1).

3. Minimum 33-mil (0.84 mm) hat section in accordance with Figure R804.3.1.3(1).

4. Minimum 54-mil (1.37 mm) 1¹/₂-inch (38 mm) cold-rolled channel section in accordance with Figure R804.3.1.3(1).

5. Minimum 1¹/₂-inch by 33-mil (38 mm by 0.84 mm) continuous steel strap in accordance with Figure R804.3.1.3(2).

Lateral bracing shall be installed perpendicular to the ceiling joists and shall be fastened to the top flange of each joist with one No. 8 screw. Blocking shall be installed between joists in line with bracing at a maximum spacing of 12 feet (3658 mm) measured perpendicular to the joists. Ends of lateral bracing shall be attached to blocking or anchored to a stable building component with two No. 8 screws.



FIGURE R804.3.1.3(1) CEILING JOIST TOP FLANGE BRACING WITH C-SHAPED, TRACK OR COLD-ROLLED CHANNEL




FIGURE R804.3.1.3(2) CEILING JOIST TOP FLANGE BRACING WITH CONTINUOUS STEEL STRAP AND BLOCKING

Splices in ceiling joists shall be permitted, if ceiling joist splices are supported at interior bearing points and are constructed in accordance with Figure R804.3.1.4. The number of screws on each side of the splice shall be the same as required for the heel joint connection in Table R804.3.1.1(3).



For SI: 1 inch = 25.4 mm

FIGURE R804.3.1.4 SPLICED CEILING JOISTS