Double Floor Joist

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.

Double floor joist. Tji joists are occasionally doubled to support other members or loads from above. Double floor joists are two joists side by side that are usually nailed or screwed together along the length. This allows you to install a supporting post off the double floor joist to hold a second storey or a. Why would you use a double floor joist.

Double and triple joist hangers. True floor joist span calculations can only be made by a structural engineer or contractor. 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. 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.

In these cases the joist hangers will be 4 by 6 inches 6 by 6 or 6 by 8 depending on the dimensions of the joists. Depending on how the load is applied it may be necessary to connect the two joists together with a filler block.