Observation: Springiness, bounce, shaking, vibration, or visible sag indicates excessive deflection of beams, joists, or rafters.
Performance Standard: All beams, joists, rafters, headers, and other structural members shall be sized, and fasteners spaced, l according to appropriate building codes, National Forest Products
Association span tables, or a higher standard agreed upon before construction by the owner and the remodeler.
Corrective Measure: The remodeler will reinforce or modify, as necessary, any floor, wall, ceiling, or roof not meeting the performance standard.
Discussion: Excessive deflection may indicate insufficient stiffness in the lumber, or may reflect an aesthetic consideration independent of the strength and safety requirements of the lumber. Joists and rafters are required to meet standards for both stiffness and strength. The span tables allow, under full design loadings, a maximum deflection equal to 1/360 of the span for floor and ceiling joists (3/8 inch in 12 feet), 1/240 for rafters up to 3/12 in pitch (1/2 inch in 12 feet), and 1/180 for rafters over 3/12 in pitch (3/4 inch in 12 feet). Individual clients may not be satisfied with the deflection limits built into the tables. When a customer’s preference is made known before construction, a higher standard may be agreed upon by the remodeler and the owner.
