The Brazilian standards of structures in fire prescribe minimum dimensions for the ribbed slabs to ensure fire resistance. However, a new composite ribbed slab is not covered by any of the Brazilian standards in fire. The objective of this work is to present unpublished results from numerical and thermal analyses for this type of slab. Ribbed slabs filled with cell concrete blocks, ceramic bricks and EPS supported by cimentitious board were studied. The constructive element is considerate as thermal insulation if it has the capacity to prevent the occurrence, on the face non exposed to fire, temperature increments greater than 140 °C on the average or greater than 180 ºC at any point. The support function
was determined limiting the temperature of the beams and slabs rebars to 500 ºC. The analyses were carried out with the ATERM and Super
Tempcalc, software for two-dimensional thermal analysis by means of the finite element method. As a result, tables will be presented that link the fire resistance required time to slab dimensions and position of rebar. Prior to use in designing these results must be confirmed by experimental analysis, which is already being provided.