Develops a steady state solution to determine the thermal interaction between a slab-on-grade floor and above-grade walls. In particular, the thermal bridging effects at the slab/wall joints are evaluated for various insulation configurations. Using a finite different numerical technique and temperature field within the building envelope and the soil, determines and analyses the heat flux profiles along the foundation surfaces and the total slab and wall heat losses for both interior and external insulation configurations. Finds that a significant thermal interaction exists between the slab-on-grade floor and the above-grade walls. In particular, finds that adding thermal insulation to the slab or to the walls affects the thermal performance of both the slab and the walls.KEYWORDS: year 1997, Calculating, thermal bridges, performance, foundations, floors, walls, slabs, thermal insulation