R804.3 Roof Construction

Cold-formed steel roof systems constructed in accordance with the provisions of this section shall consist of both ceiling joists and rafters in accordance with Figure R804.3 and fastened in accordance with Table R804.3.




FIGURE R804.3 COLD-FORMED STEEL ROOF CONSTRUCTION

TABLE R804.3 ROOF FRAMING FASTENING SCHEDULE^{a, b}

DESCRIPTION OF BUILDING ELEMENTS			NUMBER AND SIZE OF FASTENERSa				SPACING OF FASTENERS
Roof sheathing (oriented strand board or plywood) to rafter			No. 8 screws				6″ o.c. on edges and 12″ o.c. at interior supports. 6″ o.c. at gable end truss
Gable end truss to end wall top track			No. 10 screws				12″ o.c.
Rafter to ceiling joist			Minimum No. 10 screws, in accordance with Table R804.3.1.1(3)				Evenly spaced, not less than 1/2″ from all edges.
Ceiling joist or roof truss to top track of bearing wallb	Ceiling Joist Spacing (in.)	Roof Span (ft)	Ultimate Design Wind Speed (mph) and Exposure Category				Each ceiling joist or roof truss
			126 B 110 C	<139 B 115 C	126 C	<139 C
	16	24	2	2	2	3
		28	2	2	3	3
		32	2	2	3	4
		36	2	2	3	4
		40	2	2	3	4
	24	24	2	2	3	4
		28	2	2	4	5
		32	2	3	4	5
		36	2	3	4	6
		40	2	3	5	6

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

a. Screws are a minimum No. 10 unless noted otherwise.

b. Indicated number of screws shall be applied through the flanges of the truss or ceiling joist or through each leg of a 54 mil clip angle. See Section R804.3.8 for additional requirements to resist uplift forces.

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

Cold-formed steel roof rafters shall be in accordance with this section.

Roof rafter size and thickness shall be determined in accordance with the limits set forth in Table R804.3.2.1(1) based on the horizontal projection of the roof rafter span. For determination of roof rafter sizes, reduction of roof spans shall be permitted where a roof rafter support brace is installed in accordance with Section R804.3.2.2. The reduced roof rafter span shall be taken as the larger of the distances from the roof rafter support brace to the ridge or to the heel measured horizontally.

For the purpose of determining roof rafter sizes in Table R804.3.2.1(1), ultimate design wind speeds shall be converted to equivalent ground snow loads in accordance with Table R804.3.2.1(2). Roof rafter sizes shall be based on the higher of the ground snow load or the equivalent snow load converted from the ultimate design wind speed.

TABLE R804.3.2.1(1) ROOF RAFTER SPANS^{a, b, c, d}

MEMBER DESIGNATION	ALLOWABLE SPAN MEASURED HORIZONTALLY (feet - inches)
	Ground snow load (psf)
	20		30		50		70
	Rafter spacing (inches)
	16	24	16	24	16	24	16	24
550S162-33	14'-0″	11'-6″	11'-11″	9'-7″	9'-6″	7'-9″	8'-2″	6'-8″
550S162-43	16'-8″	13'-11″	14'-5″	11'-9″	11'-6″	9'-5″	9'-10″	8'-0″
550S162-54	17'-11″	15'-7″	15'-7″	13'-8″	13'-2″	11'-6″	11'-9″	10'-3″
550S162-68	19'-2″	16'-9″	16'-9″	14'-7″	14'-1″	12'-4″	12'-7″	11'-0″
800S162-33	16'-5″	13'-5″	13'-11″	11'-4″	11'-1″	8'-2″	9'-0″	6'-0″
800S162-43	19'-9″	16'-1″	16'-8″	13'-7″	13'-4″	10'-10″	11'-5″	9'-4″
800S162-54	24'-2″	21'-2″	21'-1″	18'-5″	17'-10″	14'-8″	15'-5″	12'-7″
800S162-68	25'-11″	22'-8″	22'-8″	19'-9″	19'-1″	16'-8″	17'-1″	14'-9″
1000S162-43	22'-3″	18'-2″	18'-9″	15'-8″	15'-0″	12'-3″	12'-10″	10'-6″
1000S162-54	29'-0″	24'-6″	25'-4″	20'-9″	20'-3″	16'-7″	17'-5″	14'-2″
1000S162-68	31'-2″	27'-3″	27'-3″	23'-9″	20'-0″	19'-6″	20'-6″	16'-8″
1200S162-54	33'-2″	27'-1″	28'-1″	22'-11″	22'-5″	18'-4″	19'-3″	15'-8″
1200S162-68	36'-4″	31'-9″	31'-9″	27'-0″	26'-5″	21'-6″	22'-6″	18'-6″

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

a. Table provides maximum horizontal rafter spans in feet and inches for slopes between 3:12 and 12:12.

b. Deflection criteria: L/240 for live loads and L/180 for total loads.

c. Roof dead load = 12 psf.

d. Grade 33 ksi steel is permitted to be used for 33 mil and 43 mil thicknesses. Grade 50 ksi steel shall be used for 54 and 68 mil thicknesses.

TABLE R804.3.2.1(2) ULTIMATE DESIGN WIND SPEED TO EQUIVALENT SNOW LOAD CONVERSION

BASIC WIND SPEED AND EXPOSURE		EQUIVALENT GROUND SNOW LOAD (psf)
		Roof slope
Exp. B	Exp. C	3:12	4:12	5:12	6:12	7:12	8:12	9:12	10:12	11:12	12:12
85 mph	‒	20	20	20	20	20	20	30	30	30	30
100 mph	85 mph	20	20	20	20	30	30	30	30	50	50
110 mph	100 mph	20	20	20	20	30	50	50	50	50	50
‒	110 mph	30	30	30	50	50	50	70	70	70	‒

Eave overhangs shall not exceed 24 inches (610 mm) measured horizontally.

Rake overhangs shall not exceed 12 inches (305 mm) measured horizontally. Outlookers at gable endwalls shall be installed in accordance with Figure R804.3.2.1.2.




FIGURE R804.3.2.1.2 GABLE ENDWALL OVERHANG DETAILS

When used to reduce roof rafter spans in determining roof rafter sizes, a roof rafter support brace shall meet all of the following conditions:

1. Minimum 350S162-33 C-shaped brace member with maximum length of 8 feet (2438 mm).

2. Minimum brace member slope of 45 degrees (0.785 rad) to the horizontal.

3. Minimum connection of brace to a roof rafter and ceiling joist with four No.10 screws at each end.

4. Maximum 6 inches (152 mm) between brace/ceiling joist connection and load-bearing wall below.

5. Each roof rafter support brace greater than 4 feet (1219 mm) in length, shall be braced with a supplemental brace having a minimum size of 350S162-33 or 350T162-33 such that the maximum unsupported length of the roof rafter support brace is 4 feet (1219 mm). The supplemental brace shall be continuous and shall be connected to each roof rafter support brace using two No. 8 screws.

Roof rafters shall not be spliced.

Roof rafters shall be connected to a parallel ceiling joist to form a continuous tie between exterior walls in accordance with Figure R804.3.1.1 and Table R804.3.1.1(3). Ceiling joists shall be connected to the top track of the load-bearing wall in accordance with Table R804.3, either with the required number of No. 10 screws applied through the flange of the ceiling joist or by using a 54-mil (1.37 mm) clip angle with the required number of No.10 screws in each leg. Roof rafters shall be connected to a ridge member with a minimum 2-inch by 2-inch (51 mm by 51 mm) clip angle fastened with No. 10 screws to the ridge member in accordance with Figure R804.3.2.4 and Table R804.3.2.4. The clip angle shall have a steel thickness equivalent to or greater than the roof rafter thickness and shall extend the depth of the roof rafter member to the extent possible. The ridge member shall be fabricated from a C-shaped member and a track section that shall have a minimum size and steel thickness equivalent to or greater than that of adjacent roof rafters and shall be installed in accordance with Figure R804.3.2.4. The ridge member shall extend the full depth of the sloped roof rafter cut.




FIGURE R804.3.2.4 RIDGE MEMBER CONNECTION

TABLE R804.3.2.4 SCREWS REQUIRED AT EACH LEG OF CLIP ANGLE FOR ROOF RAFTER TO RIDGE MEMBER CONNECTION^a

BUILDING WIDTH (feet)	NUMBER OF SCREWS
	Ground snow load (psf)
	0 to 20	21 to 30	31 to 50	51 to 70
24	2	2	3	4
28	2	3	4	5
32	2	3	4	5
36	3	3	5	6
40	3	4	5	7

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

a. Screws shall be No. 10 minimum.

The bottom flanges of roof rafters shall be continuously braced, at a maximum spacing of 8 feet (2440 mm) as measured parallel to the roof rafters, with one of the following members:

1. Minimum 33-mil (0.84 mm) C-shaped member.

2. Minimum 33-mil (0.84 mm) track section.

3. Minimum 1¹/₂-inch by 33-mil (38 mm by 0.84 mm) steel strap.

The bracing element shall be fastened to the bottom flange of each roof rafter with one No. 8 screw and shall be fastened to blocking with two No. 8 screws. Blocking shall be installed between roof rafters in-line with the continuous bracing at a maximum spacing of 12 feet (3658 mm) measured perpendicular to the roof rafters. The ends of continuous bracing shall be fastened to blocking or anchored to a stable building component with two No. 8 screws.

Flanges and lips of load-bearing, cold-formed steel roof framing members shall not be cut or notched.

Roof-ceiling framing above wall openings shall be supported on headers. The allowable spans for headers in load-bearing walls shall not exceed the values set forth in Section R603.6 and Tables R603.6(1) through R603.6(6).

Openings in roofs and ceilings shall be framed with header and trimmer joists. Header joist spans shall not exceed 4 feet (1219 mm) in length. Header and trimmer joists shall be fabricated from joist and track members having a minimum size and thickness equivalent to the adjacent ceiling joists or roof rafters and shall be installed in accordance with Figures R804.3.5(1) and R804.3.5(2). Each header joist shall be connected to trimmer joists with not less than four 2-inch by 2-inch (51 by 51 mm) clip angles. Each clip angle shall be fastened to both the header and trimmer joists with four No. 8 screws, evenly spaced, through each leg of the clip angle. The steel thickness of the clip angles shall be not less than that of the ceiling joist or roof rafter. Each track section for a built-up header or trimmer joist shall extend the full length of the joist (continuous).




FIGURE R804.3.5(1) ROOF OR CEILING OPENING




FIGURE R804.3.5(2) HEADER TO TRIMMER CONNECTION

Cold-formed steel trusses shall be designed and installed in accordance with AISI S100, Section D4. In the absence of specific bracing requirements, trusses shall be braced in accordance with accepted industry practices, such as the SBCA Cold-Formed Steel Building Component Safety Information (CFSBCSI) Guide to Good Practice for Handling, Installing & Bracing of Cold-Formed Steel Trusses. Trusses shall be connected to the top track of the load-bearing wall in accordance with Table R804.3, either with two No. 10 screws applied through the flange of the truss or by using a 54-mil (1.37 mm) clip angle with two No. 10 screws in each leg.

Ceiling and roof diaphragms shall be in accordance with this section.




FIGURE R804.3.7.2 ROOF BLOCKING DETAIL

At gable endwalls a ceiling diaphragm shall be provided by attaching a minimum ¹/₂-inch (12.7 mm) gypsum board or a minimum ³/₈-inch (9.5 mm) wood structural panel sheathing, that complies with Section R803, to the bottom of ceiling joists or roof trusses and connected to wall framing in accordance with Figures R804.3.7.1(1) and R804.3.7.1(2), unless studs are designed as full height without bracing at the ceiling. Flat blocking shall consist of C-shaped or track section with a minimum thickness of 33 mils (0.84 mm). For a gypsum board sheathed ceiling, the diaphragm length shall be in accordance with Table R804.3.7.1. For a wood structural panel sheathed ceiling, the diaphragm length shall be not less than 12 feet (3658 mm) for building widths less than 36 feet (10 973 mm), or not less than 14 feet (4267 mm) for building widths greater than or equal to 36 feet (10 973 mm).

The ceiling diaphragm shall be secured with screws spaced at a maximum 6 inches (152 mm) o.c. at panel edges and a maximum 12 inches (305 mm) o.c. in the field. The required lengths in Table R804.3.7.1 for gypsum board sheathed ceiling diaphragms shall be permitted to be multiplied by 0.35 if all panel edges are blocked. Multiplying the required lengths in Table R804.3.7.1 for gypsum board sheathed ceiling diaphragms by 0.9 shall be permitted if all panel edges are secured with screws spaced at 4 inches (102 mm) o.c.

TABLE R804.3.7.1 REQUIRED LENGTHS FOR CEILING DIAPHRAGMS AT GABLE ENDWALLS GYPSUM BOARD SHEATHED, CEILING HEIGHT = 8 FEET^{a, b, c, d, e, f, g}

EXPOSURE CATEGORY		ULTIMATE DESIGN WIND SPEED (mph)
B		126	< 139	‒	‒
C		110	‒	126	< 139
Roof pitch	Building endwall width (feet)	Minimum diaphragm length (feet)
3:12 to 6:12	24 - 28	20	22	28	32
	> 28 - 32	22	28	32	38
	> 32 - 36	26	32	38	44
	> 36 - 40	30	36	44	50
6:12 to 9:12	> 24 - 28	22	26	32	36
	> 28 - 32	26	32	38	44
	> 32 - 36	32	38	44	52
	> 36 - 40	36	44	52	60
9:12 to 12:12	> 24 - 28	26	30	36	42
	> 28 - 32	30	36	42	50
	> 32 - 36	36	42	50	60
	> 36 - 40	42	50	60	70

For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.

a. Ceiling diaphragm is composed of 1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8 screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater than 54 mils.

b. Maximum aspect ratio (length/width) of diaphragms is 2:1.

c. Building width is in the direction of horizontal framing members supported by the wall studs.

d. Required diaphragm lengths are to be provided at each end of the structure.

e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.

f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.

g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in the table above shall be multiplied by 1.15.

FIGURE R804.3.7.1(1) CEILING DIAPHRAGM TO GABLE ENDWALL DETAIL




FIGURE R804.3.7.1(2) CEILING DIAPHRAGM TO SIDEWALL DETAIL

A roof diaphragm shall be provided by attaching a minimum of ³/₈-inch (9.5 mm) wood structural panel which complies with Section R803 to roof rafters or truss top chords in accordance with Table R804.3. Buildings with 3:1 or larger plan aspect ratio and with roof rafter slope (pitch) of 9:12 or larger shall have the roof rafters and ceiling joists blocked in accordance with Figure R804.3.7.2.

Roof assemblies shall be connected to walls below in accordance with Table R804.3. A continuous load path shall be provided to transfer uplift loads to the foundation.