Foamed concrete, comprising a cementitious paste or mortar together with preformed foam, has many attractive properties, perhaps the most useful being its excellent thermal insulation properties, and therefore it can be classified as controlled thermal fill (CTF). Although widely used as a simple backfill, foamed concrete can be designed easily for particular densities (800-1600 kg/m³), flow characteristics (100–300 mm spread), strength (typically less than 10 MPa), and thermal insulation performance (0.2–0.6 W/mK). These properties make it an ideal material for house construction, in particular, for enhancing the thermal efficiency of the foundations and ground slab. This paper examines the performance of a range of foamed concretes for trench fill foundations and ground slabs in terms of thermal performance and main engineering, permeation, and durability properties. The consonant advantages of using fly ash (low-lime, fine, and coarse) technology will also be discussed.