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.
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
COLD-FORMED STEEL ROOF CONSTRUCTION
ROOF FRAMING FASTENING SCHEDULEa, 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.
- Screws are a minimum No. 10 unless noted otherwise.
- 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.
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.
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.
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.
NUMBER OF SCREWS REQUIRED FOR CEILING JOIST TO ROOF RAFTER CONNECTIONa
| 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.
- Screws shall be No. 10.
For SI: 1 mil = 0.0254 mm.
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:
- Gypsum board shall be fastened with No. 6 screws in accordance with Section R702.
- 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:
- Minimum 33-mil (0.84 mm) C-shaped member in accordance with Figure R804.3.1.3(1).
- Minimum 33-mil (0.84 mm) track section in accordance with Figure R804.3.1.3(1).
- Minimum 33-mil (0.84 mm) hat section in accordance with Figure R804.3.1.3(1).
- Minimum 54-mil (1.37 mm) 11/2-inch (38 mm) cold-rolled channel section in accordance with Figure R804.3.1.3(1).
- 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).
CEILING JOIST TOP FLANGE BRACING WITH C-SHAPED, TRACK OR COLD-ROLLED CHANNEL
For SI: 1 foot = 304.8 mm.
CEILING JOIST TOP FLANGE BRACING WITH CONTINUOUS STEEL STRAP AND BLOCKING
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.
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.
SPLICED CEILING JOISTS
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.
ROOF RAFTER SPANSa, 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.
- Table provides maximum horizontal rafter spans in feet and inches for slopes between 3:12 and 12:12.
- Deflection criteria: L/240 for live loads and L/180 for total loads.
- Roof dead load = 12 psf.
- 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.
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 | — |
For SI: 1 mile per hour = 0.447 m/s, 1 pound per square foot = 0.0479 kPa.
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.
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
GABLE ENDWALL OVERHANG DETAILS