Floor Deflection Standard

Refer to section r703 7 2 reason.

Floor deflection standard.

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. The irc says that floors must deflect no more than 1 360 of the floor s span. Is the live load or the weight of the furniture. Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection.

The standard load designed for most residential floors to support is 50 lb. Many tile contractors can judge a floor s deflection by walking around. To calculate a specific value the tile council of north america tcna offers a standard formula. See the table below.

Is assumed to be the dead load or the weight of the building materials themselves and 40 lb. Similarly the allowable deflection for a criterium of l 240 would be 144 inches divided by 240 which is 0 6 inch. Codes also specify how much floors are allowed to bend under load a measurement called a deflection limit. Of that 10 lb.

Ft plus any. For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. The current combined row for floors and ceilings with plaster and stucco. If the floor deflects more than the 0 4 inches or 0 6 inches the floor is deflecting more than what the standard allows and does not meet code.

Stiffness is measured by the floor s deflection under load. This is intended to be an editorial clean up and not change any current requirements for deflection criteria. For an older home the deflection usually exceeds the current code requirements. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.

For example a floor with a span of 10 feet must deflect no more than 1 3 inch or 120 inches 360 inches. The l 360 standard means that the floor should not deflect more than the span divided by 360.