The vibration reduction index (Kij) is a key parameter in the prediction of flanking transmissions according to the EN-12354 standard. Formulas for the evaluation of Kij in L, T and X junctions that depend on the mass ratio are available in the Annex E. Junctions of straight elements with different thickness or thin elastic layers are also included. However, other junction types that are important for building industry are not considered: H-shaped junctions, L or T junctions not forming a right angle, asymmetrical T-junctions , X-junctions where only one of the parts is different (thickness or material) from the other three. In the current research, expressions for these non-covered junctions are provided. They are obtained by means of numerical simulations based on the spectral and/or the standard finite element method. Kij is predicted for a large population of junctions, considering usual thicknesses and material combinations. Afterwards, an statistical treatment of the data is done in order to obtain simple but representative formulas that can easily be used in the daily acoustic projects or included in design software without the need of large computations.