Flooring Deflection On Edge

Typical deflection limits referenced in code books are l 360 l 240 or l 180.

Flooring deflection on edge.

Stiffness is measured by the floor s deflection under load. 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. See the table below.

Span tables and design values. 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. The solution to sagging floors or the damaged sills and joist ends that contribute to them often involves jacking. Drywall screws through the plywood and into joists.

Every floorboard contains both soft spring wood which is the dark grain in each board and dense late season wood. A taut string stretched across the floor will show the amount of deflection and improvement. A common scenario is to install temporary jack posts and support beams then permanent posts and beams over new footings. The screws should be no more than 4 in.

For example a floor with a span of 10 feet must deflect no more than 1 3 inch or 120 inches 360 inches. For example the maximum deflection for a joist span of 15 is 15 12 360 1 2. The irc says that floors must deflect no more than 1 360 of the floor s span. Dished out deformities in floorboards are typically caused by poor sanding techniques or by heavy wear in spring wood.

Frequently there is misunderstanding regarding deflection between joists. As a joist bends downward the lower edge bends slightly to one side or the other. Ft plus any long term deflection due to the weight of the floor. Bedrooms and habitable attic floors l 360 30 psf.

The standard load designed for most residential floors to support is 50 lb. Is the live load or the weight of the furniture. 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 the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360.

Of that 10 lb. The l 360 standard means that the floor should not deflect more than the span divided by 360. Living room floors l 360 40 psf. These limits are based on live loads and activities experienced in specific rooms of a house.

Examples of code prescribed deflection limits and live load values are. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.