Floor Deflection Standard

The current combined row for floors and ceilings with plaster and stucco.

Floor deflection standard.

Note it gives the allowable deflection based on a fractional span quantity so a larger denominator will yield less deflection. For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. For example a floor with a span of 10 feet must deflect no more than 1 3 inch or 120 inches 360 inches. 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.

Frequently there is misunderstanding regarding deflection between joists. 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. To calculate a specific value the tile council of north america tcna offers a standard formula. Deflection for exterior walls with interior gypsum board finish shall be limited to allowable deflection of h 180.

Is assumed to be the dead load or the weight of the building materials themselves and 40 lb. This is intended to be an editorial clean up and not change any current requirements for deflection criteria. Codes also specify how much floors are allowed to bend under load a measurement called a deflection limit. 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. Refer to section r703 7 2 reason. The irc says that floors must deflect no more than 1 360 of the floor s span. Many tile contractors can judge a floor s deflection by walking around.

Of that 10 lb. Stiffness is measured by the floor s deflection under load. The standard load designed for most residential floors to support is 50 lb. For an older home the deflection usually exceeds the current code requirements.

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. Similarly the allowable deflection for a criterium of l 240 would be 144 inches divided by 240 which is 0 6 inch.