The Differences Between Joisted & Post-&-Beam Floors

Joists

• Joists are lateral support boards installed between the primary beams that outline the shape of the floor. They are usually made with 2-by-4 lumber or similar 2-inch lumber sizes. The amount of space between the joists depends on the quality of the floor, the cost of the project and how much weight the joists need to bear. Joists are made from the same lumber as other framework materials.

Construction Role

• Joists play a vital support role in the construction of a house. While the beams provide shape and accuracy, much of the weight is borne by the joists. Joist construction is especially important if houses have more than one story, since joists are used on both floors. Joisted foundations are common and allow for flexible house plans and new additions.

Post and Beam

• Post-and-beam is the part of the house structure that provides overall flow and framework. The outside of the flooring and the beams that rise up from the foundation compose the post-and-beam support network across the house. Most post-and-beam lumber uses 4-by-8 posts, although sizes vary based on individual plans.

Construction Role

• Without the post-and-beam framework, the floor could not exist. But when people refer to a post-and-beam floor, they usually mean a floor that has many posts and beams that provide direct support right from the foundation. As a result, joists may still be used but are not as important and occupy a secondary role in weight bearing. Focusing on post-and-beam work is generally more expensive, but provides a strong framework for simple house designs.