Wall-building element system comprising sole elements, basic wall-building elements adapted to be assembled to a wall, and beams adapted to be fitted between each horizontal layer of the basic wall-building elements. The basic wall-building elements are prefabricated with a central, load bearing core member and form-stable layers of thermal insulation on both sides thereof. The core member and the thermal insulation layers are mutually adapted in a tongue-and-groove system while the beams are made in an H-profile corresponding thereto. The core member typically consists of a plate-shaped main body provided with laterally extending, vertically oriented ribs.

Building techniques and structures to fabricate components of expanded polystyrene (EPS) for assembly into a building include structures and ways to make keys to provide shear strength between components, structures and ways to minimize infiltration paths between walls and floors and walls and roof while reducing labor, material wastage and logistics complications. By way of example, components are strategically cut from a block of EPS using a hot wire moving through the block to cut components to a desired and novel configuration.