© 2019 by the authors. The building sector is considered a key area for sustainable development, due to the potential to reduce greenhouse gas emissions in the numerous economic activities that this sector involves. A low-cost lightweight cementitious composite consisting in perlite mortar was fabricated and evaluated. The thermal conductivity and heat capacity of the proposed composite were tested in the laboratory. The lightweight composite was integrated into a prototypical house and its thermal performance was tested for two different arid climates during a typical meteorological year. A techno-economic analysis of this integration was carried out, which showed the lightweight system integration could reduce the energy demand up to 10.3% due to the decreased use of heating and cooling systems. The CO2 emissions associated with electricity and gas use on cooling and heating systems could be reduced up to 10.9%.