Electrical & Electric

Floor Joist and Joist Hangers

Solid Wood and Engineered Floor Joist

Floor joists are the supporting members that run from wall to wall or wall to a center beam to support a buildings floor. In residential construction the floor joists are made of wood. In commercial construction they are usually made of steel or concrete. The floor joist sits on top of the foundation sill plate and runs across the span to a center beam and continues to the opposite wall. A second option is the joist can be hung with joist hangers.  

The span of the floor depends on the size of the joist. A rough rule of thumb is that the width of the joist in inches is half the span in feet plus two inches. Thus, a span of 14 feet is seven plus two inches or 9 inches. This means that the 14 feet span will require a standard 2 X 10 floor joist. 

Engineered floor joists have rapidly taken the place of solid lumber floor joists. They are much cheaper, stronger and can be designed to span much larger spaces than a solid wood joist. In most modern residential construction engineered floor joists have become the preferred building material.

Floor joists, either solid wood or engineered joists, can either set on top of the foundation wall or they can be hung from the wall and center beam using floor joist hangers. Joist hangers are made of galvanized steel and are attached to the wall and joist using special nails. The nails are heavy duty and have a special galvanized coating that resists rust and corrosion from chemicals found in modern day lumber.  Never use roofing nails or standard nail gun nails to attach joist hangers as they are not designed for floor loads.  Although joist hangers may not look very strong they are designed to support the floor load that the joist is designed for.

Galvanized floor joist hangers are widely used in deck construction to hang the floor (deck) joists on the side of the building. They are also widely used in second story building construction to hang engineered joists over wide spans. They come in all sizes and are very flexible. On the down side, they are often difficult to work with because they are nailed in place by hand.

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