Double Floor Joist

Double floor joists are two joists side by side that are usually nailed or screwed together along the length.

Double floor joist. Dead load weight of structure and fixed loads 10 lbs ft 2. Maximum span of 2x10 floor joist maximum span of 2x12 floor joist the most important design choices to consider when building a home are the species and grade of wood that is being used as well as joist size and spacing. The extra two inches of vertical distance when a floor is framed with 2 x 10 joists rather than 2 x 12s can be quite important for example.

Why would you use a double floor joist. Live load is weight of furniture wind snow and more. These elements will greatly affect how far you can span your joists.

1 psf lb f ft 2 47 88 n m 2. The distance y doubles since the beam is twice as deep. 1 ft 0 3048 m.

Most floor joists consist of 2 by 6 inch lumber but they can use 2 by 8 or 2 by 10 as well which will require longer joist hangers. The main reason for doubling up floor joists is to double the strength of a single floor joist. However if the loading is applied from above through floor sheathing through a load bearing wall or post that rests on both joists then no attachment between joists is required.

If you double the depth of a beam say by attaching a second 2x4 to the bottom of the first 2x4 thereby changing the depth from 1 3 4 inches to 3 1 2 inches you increase the moment of inertia by a factor of 8 since d doubles and i goes as the cube of the depth. When a load is applied to one side of a double joist by another joist or header for example then the double joist must be connected together so both joist members are effective in supporting the load. Double and triple joist hangers double and triple joist hangers are wider to accommodate either a thicker piece of lumber or two or three joists placed side by side.

2 grade of douglas fir are indicated below.