Use the span tables below to determine allowable lengths of joists and rafters based on size and standard design loads.
Floor joist and beam.
Beams are large horizontal members that carry the floor loads from the floors walls or roofs to the columns or foundation walls.
Though joists may be any size that you desire using typical floor joist and beam specifications ensures that you can find hardware to fit the joists and that the floor provides adequate support for furniture and other items in a room.
True floor joist span calculations can only be made by a structural engineer or contractor.
Floor joists rest directly on beams.
Floor joists or beams provide the below surface support for the wood subfloor of a room.
I joists provide a high performance alternative to dimension lumber joists for floor and roof applications.
Joists and beams have many similarities but they differ in size and the role they play.
Both are horizontal members meaning they are installed level with the ground or floor below and both are supported on their ends and sometimes in their middles by load bearing walls columns or other types of vertical supports.
The supported length shown along the left most side of the table is the total length of the floor joists to be supported on either side of the floor beam divided by two.
Joists and beams are two types of structural elements that have similar and related functions in home construction.
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.
Joists are small numerous and supported by a beam.
Walls and columns often sit on floors so they may rest indirectly on beams.
You can also use the wood beam calculator from the american wood council website to determine maximum rafter and joist lengths.
A joist is a horizontal structural member used in framing to span an open space often between beams that subsequently transfer loads to vertical members.
Beams are large few in number and supported by a foundation posts or a wall.
When a load is applied to a joist the wood fibers along the bottom edge go into tension and those along the top go into compression fig.
Dividing by two gives us 12 feet of supported length.
When incorporated into a floor framing system joists serve to provide stiffness to the subfloor sheathing allowing it to function as a horizontal diaphragm.
