Flooring Deflection On Edge

Every floorboard contains both soft spring wood which is the dark grain in each board and dense late season wood.

Flooring deflection on edge.

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 screws should be no more than 4 in. The solution to sagging floors or the damaged sills and joist ends that contribute to them often involves jacking. The l 360 standard means that the floor should not deflect more than the span divided by 360.

Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. A common scenario is to install temporary jack posts and support beams then permanent posts and beams over new footings. For example the maximum deflection for a joist span of 15 is 15 12 360 1 2. The soft spring wood in this floor was dug out by improper sanding.

These limits are based on live loads and activities experienced in specific rooms of a house. Ft plus any long term deflection due to the weight of the floor. Drywall screws through the plywood and into joists. Is the live load or the weight of the furniture.

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. Typical deflection limits referenced in code books are l 360 l 240 or l 180. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.

Span tables and design values. Examples of code prescribed deflection limits and live load values are. Stiffness is measured by the floor s deflection under load. A layer of 3 4 in.

Frequently there is misunderstanding regarding deflection between joists. 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. Living room floors l 360 40 psf. A taut string stretched across the floor will show the amount of deflection and improvement.

As a joist bends downward the lower edge bends slightly to one side or the other. Of that 10 lb. Is assumed to be the dead load or the weight of the building materials themselves and 40 lb. See the table below.

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