A steady-periodic solution for the heat conduction problem under a slab-on-grade floor adjacent to another slab is presented. The two slabs can be uninsulated or uniformally insulated. A water table is assumed to exist at finite depth from the soil surface. The interzone temperature profile estimation technique is used to develop a semi-analytical solution for the heat conduction equation in the ground medium. The soil temperature field, and the total slab heat loss are obtained and analysed in detail. The effect of the distance that separates the adjacent slabs on the mean and amplitude of total slab heat loss is discussed.