Depth Of Floor Joists

Joist span and spacing is set by your local building code.

Depth of floor joists.

The rule of thumb for the depth of common joists is to take half span in feet. 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. E g for a span of 18 feet. Limit the length of notches to one third of the joist depth.

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. 2 grade of douglas fir are indicated below. Live load is weight of furniture wind snow and more. So our house would look like the picture below with all floor joists 2 x 8.

The same floor if framed with 2 by 12s will be 13 1 4 inches thick. Builders can adjust their choice of lumber size and spacing depending on circumstances. The floor joist spacing is the distance between the centers of any two installed joists. 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.

Reading the table you ll see that 2 x 8s installed 16 apart on center can span 12 4. See the image below for an example of joists spaced 16 on center 16 o c. Maximum notch depth in the outer third of a joist is one sixth of the joist depth. Dead load weight of structure and fixed loads 10 lbs ft 2.

Joists in home construction are usually made with 2 by 10 or 2 by 12 lumber. To this number add 2 for the depth of the joist in inches. 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. No notching in the middle third of a joist.

1 psf lb f ft 2 47 88 n m 2. For 19 32 and 5 8 inch panels joists should be 16 or 20 inches on center. 1 ft 0 3048 m. Half this is 9 add 2 which gives 11 inches for the depth.

You should check with your local building department for construction requirements in your area. When accounting for joist width subflooring flooring and standard ceiling drywall a floor framed with 2 by 10s will be very close to 11 1 4 inches thick. Maximum floor joist span for no. No notching or boring anywhere.