Si-C-H-O-containing radicals are important intermediates during the combustion and pyrolysis of precursors applied for the gas-phase synthesis of silica nanoparticles. Despite the industrial importance of silica nanoparticles, a comprehensive thermodynamics database of organosilane species is still missing. This work presents thermochemical data of 91 Si-C-H-O radical species. Quantum-chemical calculations and isodesmic reaction schemes are used to determine the standard enthalpy of formation, entropy, and heat capacities covering the 298-2000 K temperature range. In addition, 90 group-additivity values (GAVs) are calculated, which cover all relevant group increments. A combinatorial approach is used to ensure that all possible group increments are considered. The theoretically calculated species are used as a training set to derive 90 GAVs of Si-C-H-O radical species for the first time. In addition, uncertainty contributions of GAVs were estimated. These uncertainty estimates also comprise GAVs that were previously derived to compute thermochemical data of stable Si-C-H species and radicals as well as stable Si-C-H-O compounds. Therefore, uncertainty contributions of GAVs for a whole set of 243 group increments used to predict thermochemical data of Si-organic species are reported.