Methods of this invention relate to filling gaps on substrates with a solid dielectric material by forming a flowable film in the gap. The flowable film provides consistent, void-free gap fill. The film is then converted to a solid dielectric material. In this manner gaps on the substrate are filled with a solid dielectric material. According to various embodiments, the methods involve reacting a dielectric precursor with an oxidant to form the dielectric material. In certain embodiments, the dielectric precursor condenses and subsequently reacts with the oxidant to form dielectric material. In certain embodiments, vapor phase reactants react to form a condensed flowable film.