page_title: Waffle slab
section_title: Waffle slab design
hierarchical_section_title: Waffle slab / Construction process / Waffle slab design
caption_attribution_description: English: Diagram shows Slab and Rib width with rules of thumb formula
context_page_description: A waffle slab or two-way joist slab is a concrete slab made of reinforced concrete with concrete ribs running in two directions on its underside. The name waffle comes from the grid pattern created by the reinforcing ribs. Waffle slabs are preferred for spans greater than 40 feet, as they are much stronger than flat slabs, flat slabs with drop panels, two-way slabs, one-way slabs, and one-way joist slabs.
context_section_description: Different guides have been made for architects and engineers to determine various parameters of waffle slabs, primarily the overall thickness and rib dimensions. The following are rules of thumb, which are explained further in the accompanying diagrams:
  Slab depth is typically 75 mm (3 in) to 130 mm (5 in) thick. As a rule of thumb, the depth should be ​¹⁄₂₄ of the span.
  The width of the ribs is typically 130 mm (5 in) to 150 mm (6 in), and ribs usually have steel rod reinforcements.
  The distance between ribs is typically 915 mm (3 ft).
  The height of the ribs and beams should be ​¹⁄₂₅ of the span between columns.
  The width of the solid area around the column should be ​¹⁄₈ of the span between columns. Its height should the same as the ribs.
caption: Diagram shows slab and rib width with rules of thumb formula
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