| Summary: | A numerical model based on a two-dimensional finite-volume implicit procedure is utilized for the determination of the thermal performance of Hordi (rib-slab) roofs used in the construction of buildings in Saudi Arabia. The roofs are subjected to periodic change in ambient temperature, solar radiation and nonlinear radiation exchange on the outside surface and to a constant indoor-air-temperature on the inside surface. The investigation is carried out under the climatic conditions of Riyadh for a representative day for July. The daily heat transmission load and dynamic R-value, averaged over a 24-hour period, are compared by using different materials for the Hordi units for the cases without and with an insulation layer. The results show that using insulation materials for the Hordi units, instead of the commonly used building materials, reduces the roof heat transmission load by about 25%. However, the ribs of the reinforced concrete slab act as thermal bridges which significantly reduce the R-value. It is concluded that using low thermal conductivity Hordi units is advantageous but does not, generally, produce sufficient thermal resistance for the uninsulated roofs. It is recommended that the ends of the ribs should be insulated. Keywords: Hordi roofs, heat transmission load, R-value, thermal insulation
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