Floor Joist Stiffness

When incorporated into a floor framing system joists serve to provide stiffness to the subfloor sheathing allowing it to function as a horizontal diaphragm joists are often doubled or tripled placed side by side where conditions warrant.

Floor joist stiffness. Details if the existing floor joists are bowed downward noticeably they might need to be jacked up slightly to make installing the new joists easier. You can notch and bore joists without sacrificing critical strength but you must follow the rules. 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. Joist properties are manually assigned for each individual floor in a simulatedrun.

Trusses are the combined structures that are composed of beams rafters joists and purlins. Truss is the name given to the full assembly of elements that supports a sloped roof. Span stiffness of subflooring tends to reduce differences in the joist deflections when a floor is subjected to uniform loading 8 10 11. Joists are a special kind of beam that support a broad flat surface.

It makes the floor stiff without creating obstructions in the basement but it s more expensive 8 to 12 per joist than other methods and won t work if you have plumbing or electrical lines mounted to the underside of the joists. Care must be taken if the joists continue into another occupancy. Continuity continuous joists over several supports generally perform better than simple spans. Thus this two way action diminishes the effects of variation in joist stiffness and tends to justify the practice of designing on the basis of equal stiffness for all the joists.

When new homes are built the truss may be. 6 mode 6 presents strength as well as stiffness estimates using joist mor values. If the bounce is severe enough he may use an engineered or laminated veneer lumber lvl beam. Still stronger is a flitch beam which uses a steel plate.

Doubling the thickness of joists by adding material to their sides increases strength and stiffness. For joists made of sawn lumber shown here tom attaches a 2x of the same length and width. To minimize future squeaks spread con struction adhesive onto both the existing joist and the new joist. They also help give stiffness to the roof.

Joist spacing and deck stiffness reduced spacing or increased deck thickness generally improves floor. The notching and boring rules of thumb for solid lumber are shown in fig.