Floor and Roof 'Wood Joist' Table
Based on 1000 psi fiber stress and L/360 deflection
Nominal
Size
Spacing
(inches)
Maximum Allowable Span for Uniform Loading
67 psf 57psf 47 psf 37 psf 22 psf
2 x 6 12 8'-9" 9'-5" 10'-4" 11'-8" 15'-1"
16 7'-6" 8'-1" 9'-0" 10'-1" 13'-2"
24 6'-0" 6'-8" 7'-4" 8'-4" 10'-9"
2 x 8 12 11'-6" 12'-5" 13'-8" 15'-4" 20'-0"
16 10'-0" 10'-9" 11'-10" 13'-4" 17'-4"
24 8'-1" 8'-9" 9'-7" 10'-11" 14'-1"
2 x 10 12 14'-7" 15'-10" 17'-5" 19'-7 25'-6"
16 12'-8" 13'-9" 15'-1" 17'-0" 22'-0"
24 10'-3" 11'-2" 12'-4" 13'-11" 18'-0"
2 x 12 12 17'-9" 19'-2" 21'-2" 23'-10" ---
16 15'-4" 16'-7" 18'-4" 20'-7" 26'-10"
24 12'-6" 13'-7" 15'-0" 16'-11" 21'-10"
Caution! Care needs to be taken when using the tables. You must be sure of what type of loading you are going to place over the joists. Refer to the table below. To be sure ask your Engineer or Architect.
Definitions:

Nominal Size = Size used to order material, such as, a 2 x 4, but which is Actually 1 1/2" x 3 1/2". Therefore, when an Engineer or Architect perform the calculations on a wood member they use the Actual dimension (which is smaller than the nominal size).

Spacing = How far apart each member is installed in the horizontal plane.

Fiber Stress = The Bending Fiber Stress which determines the capacity of the member to support the load placed on it.

Maximum Allowable Span for Uniform Loading = The Distance between the end supports of the Joists or Rafters.

L/360 = the amount of deflection permitted in the Wood Joist, where L = length of the Joist in inches.
For example: 12' = 144", therefore, L/360 = 144/360 = .4" of deflection permitted (these values are set by the Codes).

Loading Conditions: (where, psf = Pounds per Square Feet)
NOTE: These Loading Conditions do not take into account any additional loads, such as, Wind Loads, Snow Loads or Rain Loads and are limited to interior, non-exposed loading conditions. Visit your Architect or Engineer to determine the final Size of your Structural members.

67 psf --- Floor Joists with plaster under, 50 psf Live Load, 17 psf Dead Load

57 psf --- Floor Joists with plaster under, 40 psf Live Load, 17 psf Dead Load
57 psf --- Roof Joists having a slope of 2 1/2 to 12 or more, 30 psf Live Load, 27 psf Dead Load

47 psf --- Floor Joists without plaster under, 40 psf Live Load, 7 psf Dead Load
47 psf --- Roof Joists with plaster under, 30 psf Live Load, 17 psf Dead Load

37 psf --- Ceiling Joists over Living Rooms and under Attic Spaces, 25 psf Live Load, 12 psf Dead Load
37 psf --- Roof Joists without plaster under, 30 psf Live Load, 7 psf Dead Load

22 psf --- Ceiling Joists without usable Attic Space, 10 psf Live Load, 12 psf Dead Load

The Span Tables have been Designed Assuming that the Wood Members have a Bending Stress = 1000 psi. Also check that the Wood Members are in Good Condition, Avoid Splits, Checked or Cracked Lumber. These Tables are to be used to Estimate the Lumber Needed for Construction and MAY ONLY BE USED FOR DESIGN BY SOMEONE WHO HAS THE KNOWLEDGE AND EXPERIENCE IN CONSTRUCTION AND SHALL TAKE INTO ACCOUNT ANY ADDITIONAL LOADING, SUCH AS, WIND LOADS, SNOW LOAD AND/OR RAIN LOADS.


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