Maximum Deflections of Reinforced Concrete Beams and Slabs

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Maximum ratios of computed deflection to span L for beams and slabs as per ACI 318: The Building Code:

Types of member	Deflection to be considered	Deflection Limit
Flat roofs not supporting or attached to non-structural elements likely to be damaged by large deflection.	Immediate deflection due to the live load.	L/180*
Floors not supporting or attached to non-structural elements likely to be damaged by large deflections.	Immediate deflection due to the live load.	L/360.
Roof or floor construction supporting or attached to non-structural elements likely to be damaged by large deflections.	That part of the total deflection that occurs after attachment of the non-structural elements (the sum of the long-term deflection due to all sustained loads and the immediate deflection due to any additional live load.***	L/480**
Roof or floor construction supporting or attached to non-structural elements not likely to be damaged by large deflections.	L/240 $

* This limit is not intended to safeguard against ponding. Ponding should be checked by suitable calculations of deflection, including the added deflections due to ponded water, and considering long-term effects of all sustained loads, camber, construction, tolerances and reliability of provisions for damage. ** this limit may be exceeded if adequate measures are taken to prevent damage due to supported or attached elements. *** the long term deflection may be reduced by the amount of deflection that occurs before attachment of the non-structural elements. $ but not greater than the tolerance provided for the non-structural elements. This limit may be exceeded if camber is provided so that the total deflection minus the camber does not exceed the limitation.

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