A description is given of a versatile method of analysis of noise transmission in buildings. This method incorporates power flow techniques and has the advantage that a unified approach is possible to both the direct and indirect transmission paths and is therefore equally applicable to transmission between rooms which are adjacent or several rooms or floors apart. The first configuration only lies within the range of classical theories. In this analysis, the building is regarded as an assembly of plate elements. Vibrational energy flows to and from each plate across common structural junctions in a manner analogous to heat transfer between bodies at different temperatures, and can also flow to and from the enclosed air volume. The solution of sets of simultaneous energy-balance equations gives the steady-state vibrational energy of each plate at their common junction. The pressure wave energy generated within a room by plate (or wall) vibrations is also predicted. The vibrational energies are predicted from the modal density, loss factor, coupling loss factor, and radiation loss factors, which are assessed theoretically and experimentally. Numerical calculations, involving a computer, yield values of the transmission coefficients of bending and longitudinal wave at cross-junctions, T-junctions and corners of reinforced concrete plates. The theory is compared with measurements involving quarter-scale models over a frequency range of measurement of 400 Hz-12·5 kHz.