Waffle Slabs - Construction, Features, Specifications

The waffle slabs are slabs with a grid system constructed at the bottom and a plain surface at the top surface of the slab. The surface on the top is normally thin and the ribs constructed at the bottom are normally in the rib form. 

The ribs of waffle slabs are constructed perpendicular to each other as shown in the figure-1. These are laid in equal depth having a uniform rib appearance. This construction type will hence provide good aesthetic features also. The waffle slabs constructed will have reinforcement laid in both directions.

Fig.1: Waffle Slabs Constructed in Auditorium

Construction of Waffle Slabs

When you look into the detailed study of waffle slab construction, it is observed that the ribs are directed from the column head or the beam. This arrangement is found to be more stable because of the construction of ribs and the reinforcement in both directions. This construction is found to be more stable and is recommended for slabs that are designed for larger spans or for the construction of the foundation.
All the ribs are directed from column heads or beams. The depth of ribs maintained is as same as the depth of the column head or beam. Because of the ribs and double reinforcement, it is more stable and recommended for larger span slabs or foundations.

Characteristics of Waffle Slab

The main characteristics of waffle slabs are mentioned below:
  • The most suitable application of waffle slabs is in areas that are flat in nature. 
  • The amount  (Volume) of the concrete used for this purpose is very less when it is compared with other forms of construction. 
  • The reinforcement and the form works are provided in a mesh form to finally obtain ribs and a waffle arrangement.
  • In order to construct beams, separate excavation is not necessary.
  • The waffle-like appearance of the bottom surface of the slab is obtained by the use of cardboard panels and pods.

Fig.2: Reinforcement and Form work details given for Waffle slab construction

Specifications of Waffle Slab Construction

Thickness of Waffle slab
85-100 mm

Thickness –Overall Depth 
300-600 mm
Rib Spacing 
 600-1500 mm
Maximum Span 
Prefabricated waffle slabs for span
Greater than 16m

When compared with a conventional concrete slab,  the waffle slab require only 70 percent of the concrete, and the steel required is 80%. The Waffle slab has good resistance against shrinkage. The shrinkage value is smaller than that of rafts and the footing slabs.

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