*Deflection criteria are optional. For roof rafters with drywall on the underside, use the stricter L/240 tables to limit deflection.
Example 1. Floor Joists. Assume a required single span of 12′-9″, dead load of 10 psf and joists spaced 16″ on center. Table F-2 (see following highlighted tables) shows that one solution is a grade of 2x8 having an Fb value of 1255 would allow a span of 12′-10″ which satisfies the condition. (Note that the recommended E value to limit deflection would be 1,600,000.) Going to the Design Value Tables, we find that as an example, 2x8 Hem Fir grade No.1 has an Fb value of 1310 for normal duration. (It also has an E value of 1,500,000 which does not satisfy the recommended deflection criteria.)
Example 2. Rafters. Assume a horizontal projected span of 13′-0″, a live load of 40 psf, dead load of 10 psf, a roof slope of 4/12 and rafters spaced 16″ on center. Since the slope is shallower than 7/12, there is no allowable reduction of the snow live load. Table R-3 shows that a 2x8 having an Fb value of 1300 would allow a span of 13′-1″ which satisfies the condition. (Note that the recommended E value to limit deflection would be 1,120,000.) Going to the Design Value Tables, we find that as an example, 2x8 Douglas Fir-Larch grade No.2 has an Fb value of 1390 for snow loading. (It also has an E value of 1,600,000 which satisfies the recommended deflection criteria.)
TABLE F- 2
FLOOR JOISTS WITH L/360 DEFLECTION LIMITS
DESIGN CRITERIA:
Deflection - For 40 psf live load.
Limited to span in inches divided by 360.
Strength - Live load of 40 psf plus dead load
of 10 psf determines the required bending design value.
Joist
Size Spacing
(in) (in) Modulus of Elasticity, E, in 1,000,000 psi
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4
12.0 8- 6 8-10 9- 2 9- 6 9- 9 10- 0 10- 3 10- 6 10- 9 10-11 11- 2 11- 4 11- 7 11- 9 11-11 12- 1 12- 3
16.0 7- 9 8- 0 8- 4 8- 7 8-10 9- 1 9- 4 9- 6 9- 9 9-11 10- 2 10- 4 10- 6 10- 8 10-10 11- 0 11- 2
2x 6 19.2 7- 3 7- 7 7-10 8- 1 8- 4 8- 7 8- 9 9- 0 9- 2 9- 4 9- 6 9- 8 9-10 10- 0 10- 2 10- 4 10- 6
24.0 6- 9 7- 0 7- 3 7- 6 7- 9 7-11 8- 2 8- 4 8- 6 8- 8 8-10 9- 0 9- 2 9- 4 9- 6 9- 7 9- 9
12.0 11- 3 11- 8 12- 1 12- 6 12-10 13- 2 13- 6 13-10 14- 2 14- 5 14- 8 15- 0 15- 3 15- 6 15- 9 15-11 16- 2
16.0 10- 2 10- 7 11- 0 11- 4 11- 8 12- 0 12- 3 12- 7 12-10 13- 1 13- 4 13- 7 13-10 14- 1 14- 3 14- 6 14- 8
2x 8 19.2 9- 7 10- 0 10- 4 10- 8 11- 0 11- 3 11- 7 11-10 12- 1 12- 4 12- 7 12-10 13- 0 13- 3 13- 5 13- 8 13-10
24.0 8-11 9- 3 9- 7 9-11 10- 2 10- 6 10- 9 11- 0 11- 3 11- 5 11- 8 11-11 12- 1 12- 3 12- 6 12- 8 12-10
12.0 14- 4 14-11 15- 5 15-11 16- 5 16-10 17- 3 17- 8 18- 0 18- 5 18- 9 19- 1 19- 5 19- 9 20- 1 20- 4 20- 8
16.0 13- 0 13- 6 14- 0 14- 6 14-11 15- 3 15- 8 16- 0 16- 5 16- 9 17- 0 17- 4 17- 8 17-11 18- 3 18- 6 18- 9
2x10 19.2 12- 3 12- 9 13- 2 13- 7 14- 0 14- 5 14- 9 15- 1 15- 5 15- 9 16- 0 16- 4 16- 7 16-11 17- 2 17- 5 17- 8
24.0 11- 4 11-10 12- 3 12- 8 13- 0 13- 4 13- 8 14- 0 14- 4 14- 7 14-11 15- 2 15- 5 15- 8 15-11 16- 2 16- 5
12.0 17- 5 18- 1 18- 9 19- 4 19-11 20- 6 21- 0 21- 6 21-11 22- 5 22-10 23- 3 23- 7 24- 0 24- 5 24- 9 25- 1
16.0 15-10 16- 5 17- 0 17- 7 18- 1 18- 7 19- 1 19- 6 19-11 20- 4 20- 9 21- 1 21- 6 21-10 22- 2 22- 6 22-10
2x12 19.2 14-11 15- 6 16- 0 16- 7 17- 0 17- 6 17-11 18- 4 18- 9 19- 2 19- 6 19-10 20- 2 20- 6 20-10 21- 2 21- 6
24.0 13-10 14- 4 14-11 15- 4 15-10 16- 3 16- 8 17- 0 17- 5 17- 9 18- 1 18- 5 18- 9 19- 1 19- 4 19- 8 19-11
Fb 12.0 718 777 833 888 941 993 1043 1092 1140 1187 1233 1278 1323 1367 1410 1452 1494
Fb 16.0 790 855 917 977 1036 1093 1148 1202 1255 1306 1357 1407 1456 1504 1551 1598 1644
Fb 19.2 840 909 975 1039 1101 1161 1220 1277 1333 1388 1442 1495 1547 1598 1649 1698 1747
Fb 24.0 905 979 1050 1119 1186 1251 1314 1376 1436 1496 1554 1611 1667 1722 1776 1829 1882
Note: The required bending design value, Fb, in pounds per square inch is shown at the bottom of each table and is applicable to all lumber sizes shown. Spans are shown in feet-inches and are limited to 26′ and less. Check sources of supply for availability of lumber in lengths greater than 20′.
TABLE C-1
CEILING JOISTS WITH L/240 DEFLECTION LIMITS
DESIGN CRITERIA:
Deflection - For 10 psf live load.
Limited to span in inches divided by 240.
Strength - Live Load of 10 psf plus
dead load of 5 psf determines the required fiber stress value.
Joist
Size Spacing
(in) (in) Modulus of Elasticity, E, in 1,000,000 psi
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4
12.0 9-10 10- 3 10- 7 10-11 11- 3 11- 7 11-10 12- 2 12- 5 12- 8 12-11 13- 2 13- 4 13- 7 13- 9 14- 0 14- 2
16.0 8-11 9- 4 9- 8 9-11 10- 3 10- 6 10- 9 11- 0 11- 3 11- 6 11- 9 11-11 12- 2 12- 4 12- 6 12- 9 12-11
2x 4 19.2 8- 5 8- 9 9- 1 9- 4 9- 8 9-11 10- 2 10- 4 10- 7 10-10 11- 0 11- 3 11- 5 11- 7 11- 9 12- 0 12- 2
24.0 7-10 8- 1 8- 5 8- 8 8-11 9- 2 9- 5 9- 8 9-10 10- 0 10- 3 10- 5 10- 7 10- 9 10-11 11- 1 11- 3
12.0 15- 6 16- 1 16- 8 17- 2 17- 8 18- 2 18- 8 19- 1 19- 6 19-11 20- 3 20- 8 21- 0 21- 4 21- 8 22- 0 22- 4
16.0 14- 1 14- 7 15- 2 15- 7 16- 1 16- 6 16-11 17- 4 17- 8 18- 1 18- 5 18- 9 19- 1 19- 5 19- 8 20- 0 20- 3
2x 6 19.2 13- 3 13- 9 14- 3 14- 8 15- 2 15- 7 15-11 16- 4 16- 8 17- 0 17- 4 17- 8 17-11 18- 3 18- 6 18-10 19- 1
24.0 12- 3 12- 9 13- 3 13- 8 14- 1 14- 5 14- 9 15- 2 15- 6 15- 9 16- 1 16- 4 16- 8 16-11 17- 2 17- 5 17- 8
12.0 20- 5 21- 2 21-11 22- 8 23- 4 24- 0 24- 7 25- 2 25- 8
16.0 18- 6 19- 3 19-11 20- 7 21- 2 21- 9 22- 4 22-10 23- 4 23-10 24- 3 24- 8 25- 2 25- 7 25-11
2x 8 19.2 17- 5 18- 1 18- 9 19- 5 19-11 20- 6 21- 0 21- 6 21-11 22- 5 22-10 23- 3 23- 8 24- 0 24- 5 24- 9 25- 2
24.0 16- 2 16-10 17- 5 18- 0 18- 6 19- 0 19- 6 19-11 20- 5 20-10 21- 2 21- 7 21-11 22- 4 22- 8 23- 0 23- 4
12.0 26- 0
16.0 23- 8 24- 7 25- 5
2x10 19.2 22- 3 23- 1 23-11 24- 9 25- 5
24.0 20- 8 21- 6 22- 3 22-11 23- 8 24- 3 24-10 25- 5 26- 0
Fb 12.0 711 769 825 880 932 983 1033 1082 1129 1176 1221 1266 1310 1354 1396 1438 1480
Fb 16.0 783 847 909 968 1026 1082 1137 1191 1243 1294 1344 1394 1442 1490 1537 1583 1629
Fb 19.2 832 900 965 1029 1090 1150 1208 1265 1321 1375 1429 1481 1533 1583 1633 1682 1731
Fb 24.0 896 969 1040 1108 1174 1239 1302 1363 1423 1481 1539 1595 1651 1706 1759 1812 1864
Note: The required bending design value, Fb, in pounds per square inch is shown at the bottom of each table and is applicable to all lumber sizes shown. Spans are shown in feet-inches and are limited to 26′ and less. Check sources of supply for availability of lumber in lengths greater than 20′.
TABLE C-2
CEILING JOISTS WITH L/240 DEFLECTION LIMITS
DESIGN CRITERIA:
Deflection - For 20 psf live load.
Limited to span in inches divided by 240.
Strength - Live Load of 20 psf plus
dead load of 10 psf determines the required bending design value.
Size Spacing
(in) (in) Joist Modulus of Elasticity, E, in 1,000,000 psi
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4
12.0 7-10 8- 1 8- 5 8- 8 8-11 9- 2 9- 5 9- 8 9-10 10- 0 10- 3 10- 5 10- 7 10- 9 10-11 11- 1 11- 3
16.0 7- 1 7- 5 7- 8 7-11 8- 1 8- 4 8- 7 8- 9 8-11 9- 1 9- 4 9- 6 9- 8 9- 9 9-11 10- 1 10- 3
2x 4 19.2 6- 8 6-11 7- 2 7- 5 7- 8 7-10 8- 1 8- 3 8- 5 8- 7 8- 9 8-11 9- 1 9- 3 9- 4 9- 6 9- 8
24.0 6- 2 6- 5 6- 8 6-11 7- 1 7- 3 7- 6 7- 8 7-10 8- 0 8- 1 8- 3 8- 5 8- 7 8- 8 8-10 8-11
12.0 12- 3 12- 9 13- 3 13- 8 14- 1 14- 5 14- 9 15- 2 15- 6 15- 9 16- 1 16- 4 16- 8 16-11 17- 2 17- 5 17- 8
