Flooring Deflection On Edge

Of that 10 lb.

Flooring deflection on edge.

Frequently there is misunderstanding regarding deflection between joists. Dished out deformities in floorboards are typically caused by poor sanding techniques or by heavy wear in spring wood. Is the live load or the weight of the furniture. For example the maximum deflection for a joist span of 15 is 15 12 360 1 2.

As a joist bends downward the lower edge bends slightly to one side or the other. See the table below. Bedrooms and habitable attic floors l 360 30 psf. If the span of the joists is 10 feet between supports then the deflection should not be more than 1 3 between the center and the end.

Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. The l 360 standard means that the floor should not deflect more than the span divided by 360. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6. The standard load designed for most residential floors to support is 50 lb.

A layer of 3 4 in. Plywood firmly fastened to the undersides of joists helps prevent this side to side bending and stiffens the floor. Examples of code prescribed deflection limits and live load values are. Living room floors l 360 40 psf.

Is assumed to be the dead load or the weight of the building materials themselves and 40 lb. A taut string stretched across the floor will show the amount of deflection and improvement. Stiffness is measured by the floor s deflection under load. Ft plus any long term deflection due to the weight of the floor.

Every floorboard contains both soft spring wood which is the dark grain in each board and dense late season wood. Divide the total span of the floor joists in inches by 360 to determine the maximum amount the floor can give in the middle under a live load of 40 lb sq. For example a floor with a span of 10 feet must deflect no more than 1 3 inch or 120 inches 360 inches. These limits are based on live loads and activities experienced in specific rooms of a house.

Span tables and design values. For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. The solution to sagging floors or the damaged sills and joist ends that contribute to them often involves jacking. The irc says that floors must deflect no more than 1 360 of the floor s span.

Drywall screws through the plywood and into joists. Typical deflection limits referenced in code books are l 360 l 240 or l 180.