Depth Of Floor Joists

Maximum floor joist span for no.

Depth of floor joists.

With the same quantity of timber the deeper the joists can be made the stiffer and stronger they are the depth can be calculated by the rules given above or those in. See the image below for an example of joists spaced 16 on center 16 o c. Dead load weight of structure and fixed loads 10 lbs ft 2. The same floor if framed with 2 by 12s will be 13 1 4 inches thick.

The bulk of the floor s thickness comes from the joists which are the horizontal beams that carry the floor s weight. The floor joist spacing is the distance between the centers of any two installed joists. So our house would look like the picture below with all floor joists 2 x 8. Live load is weight of furniture wind snow and more.

Builders can adjust their choice of lumber size and spacing depending on circumstances. Since the example house we are designing for is 12 feet wide we need to find in the floor joist span table a joist size and centering that can span 12 or wider. The rule of thumb for the depth of common joists is to take half span in feet. 1 ft 0 3048 m.

Joist span and spacing is set by your local building code. E g for a span of 18 feet. For 23 32 and 3 4 inch panels joists should be 24 inches on center. No notching in the middle third of a joist.

To this number add 2 for the depth of the joist in inches. Reading the table you ll see that 2 x 8s installed 16 apart on center can span 12 4. No notching or boring anywhere. Limit the length of notches to one third of the joist depth.

Half this is 9 add 2 which gives 11 inches for the depth. The maximum depth of a notch at the end of a joist where it rests on a wall or beam can t exceed one quarter of the joist depth. While most residential construction uses 2x8 joists with 16 inch spacing there are many other factors you need to consider when determining the proper joist span length. This sample table gives minimum floor joist sizes for joists spaced at 16 inches and 24 inches on center o c for 2 grade lumber with 10 pounds per square foot of dead load and 40 pounds of live load which is typical of normal residential construction.

For 19 32 and 5 8 inch panels joists should be 16 or 20 inches on center. Joists in home construction are usually made with 2 by 10 or 2 by 12 lumber. 2 grade of douglas fir are indicated below. You should check with your local building department for construction requirements in your area.