What is the Difference Between a Beam and a Joist?

Joist and beams are horizontal structural members that are subjected to traverse loads and are subjected to flexure. Now, when you look into a structural arrangement of wood, concrete or steel, we might see these joist and beams employed together. If both are similar horizontal structures, what makes them different? Let’s see.

As shown in the figure above, the building starts with foundation, posts or vertical elements, beams, joists and deck boards for flooring. It is clearly seen that the spacing of joists is smaller compared to the spacing of the joists. The beams support the joists, the deck boards and future loads coming over it. Hence, beam is a superior structural element in construction. Beams are supported by the vertical elements like posts and foundation.

The difference between joists and beams arise based on the size, their numbers used and the role they play in a given structure.

JOISTS	BEAMS
Joists are small in cross-section arranged in numerous numbers.	Beams have a large cross-section used in few numbers.
Joists are minor structural elements	Beams are major structural elements
Joist are supported by beams.	Beams are supported by vertical elements like wall, pillars, foundation.
Generally ceiling joists take a size of 2 x 6 inches to 2 x 12 inches.	The size of beam starts from 9 x 12 inches.
Joists are supposed to provide secondary support. They are used to support a broad flat surface like ceiling or floor.	Beams take and transfer the main structural loads coming over it, including the weight of joists. They take the weight of walls above, the floors or roofs coming over it.
Joists are closely arranged.	Beams are spaced larger than joists.
Joists are made from dimensional lumber, steel	Beams can be made from steel, engineered timer or dimension timber or concrete.
It is preferred in building long spans and multi-stored buildings	It is preferred to maintain structural integrity for high loads in industrial and residential buildings.

Technically joist can be considered as a time of beam. They take different roles in terms of load they carry and their arrangement.

You May Like to Read on:

1. What is a Beam Structure in Construction?
2. What is a Transfer Beam?