Previous studies have shown that the fire performance of hollowcore units is significantly affected by the end support conditions, but it has not been clear how the fire resistance of the overall floor system can be improved by providing side supports. The previous studies used beam grillage and shell elements to separately model the hollowcore units and the topping concrete slab using the platform of the non-linear finite element program SAFIR. The modelling method required a lot of computational resources and is not ideal to model a large floor area. This paper describes the effect of the side supports and the aspect ratio of the floor on the predicted fire resistance. It also compares the efficiencies of shell elements and short beam elements for finite element modelling of the topping concrete in fire conditions. The results show that integrating the topping concrete slab into the beam grillages reduces the complexity of the model and also provides satisfactory results. Side supports can increase the fire performance of hollowcore floor slabs provided that the spacing of the side supports does not greatly exceed the span length.