One of the most promising innovations in building materials is the introduction of titanium dioxide (TiO2). An application of these compounds consists of the development of new materials with self-cleaning properties. In this case the photocatalyst, added to cementitious materials or finishing products, promotes the oxidative decomposition of the organic materials adsorbed/deposited on the treated surfaces. The oxidation process realised by this photocatalysts is activated by the UV light, for this reason aplications on external surfaces of building or other architectural artefacts are investigated. Studies are conducted to measure the efficiency of the photoactive materials and their environmental performance.