Disadvantages of a waffle slab include difficult-to-handle penetrations, the requirement of special formwork, greater floor-to-floor height and low fire rating. Another disadvantage of waffle slabs is its long-time maintenance difficulty when built over reactive land.
Waffle slabs consist of equally spaced ribs in a two-way system. It is not a common form of construction due to its low fire rating and formwork costs. For a two-hour fire rating, a minimum of 125 millimeter rib thickness and 120 millimeter slab thickness is required.
Cost savings due to the reduced quantity of concrete and reinforcement associated with waffle slabs are offset by the complication in formwork and placing reinforcement. Formwork complication can be minimized, however, by using standard, reusable, modular formwork.
Continual monitoring during construction is required when laying waffle slabs on difficult types of soil. When working with difficult types of soil and waffle slabs, long-term considerations and calculations must be made, consistency of the land must be evaluated, and testing of the surrounding areas regarding treatment and landscaping must be performed. Adjustments such as placing a driveway on the opposite side of a building than planned may be required. Over time, problems such as cracks in the floors may develop.