Floor framing

Most residential floor framing systems are primarily made up of “joists,” horizontal framing members designed to span open spaces. Joists can be reinforced with “blocking” or “crush blocks” as needed, and tied together with floor sheathing.

Floor framing

Floor joists are typically arranged parallel to one another and span the length of the building. In the not-so-distant past, floor joists were made of solid lumber. Today, most residential flooring systems use engineered I-joists because of their long spans, light weights, dimensional stability, and excellent strength-to-cost ratios.

The joists on the perimeter of a building are typically called “rim joists” or “rim boards.” There is plenty of semantic variation here: some sources reserve the term “rim joist” for perimeter joists that are perpendicular to the floor joists and use the term “end joists” for perimeter joists that are parallel to the floor joists–together these are called “band joists.” I’ll stick with the catchall “rim joists” here since it seems to be the most common term. Rim joists prevent floor joists from rolling or twisting, carry loads from the walls above, and provide a strong surface to attach sheathing, siding, or other structures (like a deck or canopy) to. Because they’re load-bearing, rim joists are typically made of solid LSL or LVL engineered lumber between 1 1/8″ and 1 3/4″ thick.

A floor framing system can be strengthened with the addition of “blocking” between joists. Blocking is installed perpendicular to the floor joists on the interior of the structure, and provides additional reinforcement against rolling or twisting. Solid “crush blocks” can be added throughout the floor system wherever needed to carry heavy point loads from above to walls or posts below.

A floor system wouldn’t be complete without the subfloor (also called the floor sheathing). Subfloor is typically made of tongue-and-groove OSB or plywood. It provides a tremendous amount of bracing strength, and also serves as the base layer for the finished floor.Most residential floor framing systems are primarily made up of “joists,” horizontal framing members designed to span open spaces. Joists can be reinforced with “blocking” or “crush blocks” as needed, and tied together with floor sheathing.

Floor joists are typically arranged parallel to one another and span the length of the building. In the not-so-distant past, floor joists were made of solid lumber. Today, most residential flooring systems use engineered I-joists because of their long spans, light weights, dimensional stability, and excellent strength-to-cost ratios.

The joists on the perimeter of a building are typically called “rim joists” or “rim boards.” There is plenty of semantic variation here: some sources reserve the term “rim joist” for perimeter joists that are perpendicular to the floor joists and use the term “end joists” for perimeter joists that are parallel to the floor joists–together these are called “band joists.” I’ll stick with the catchall “rim joists” here since it seems to be the most common term. Rim joists prevent floor joists from rolling or twisting, carry loads from the walls above, and provide a strong surface to attach sheathing, siding, or other structures (like a deck or canopy) to. Because they’re load-bearing, rim joists are typically made of solid LSL or LVL engineered lumber between 1 1/8″ and 1 3/4″ thick.

A floor framing system can be strengthened with the addition of “blocking” between joists. Blocking is installed perpendicular to the floor joists on the interior of the structure, and provides additional reinforcement against rolling or twisting. Solid “crush blocks” can be added throughout the floor system wherever needed to carry heavy point loads from above to walls or posts below.

A floor system wouldn’t be complete without the subfloor (also called the floor sheathing). Subfloor is typically made of tongue-and-groove OSB or plywood. It provides a tremendous amount of bracing strength, and also serves as the base layer for the finished floor.

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