Selection and designing of noise protection aids in industrial buildings require numerous calculations of energy characteristics typical for noise fields of their facilities. The efficiency of designed soundproof measures is relying on their accuracy. The degree of accuracy is defined by recording completeness in the method of measurement of factors, which affect the processes of noise fields in buildings. One of these factors is the type of sound refection from barriers. The analysis of reflected sound energy distribution revealed that sound reflection in industrial buildings follows mirror-scattered pattern. It forms two reflected fields, mirror-like and diffusely scattered, where reflected sound energy originates and propagates on different principles. The paper offers a combined method for calculation of energy characteristics of such fields; specular reflected energy is calculated by ray tracing, and diffusely scattered one is calculated by a numerical energy method. The paper describes the basic principles for making the combined design model and offers scattering factors of reflexible sound energy that are necessary for the implementation of design model and were obtained from experiments and calculations. The accuracy of the combined method was assessed by a comparative analysis, and experimental and calculation data in production facilities of various proportions. Disagreement between calculations and experiments did not exceed 2 dB. The method fits for solving problems of construction acoustic aids of noise reduction in industrial buildings. Unlike the existing methods, in the proposed method the real process of gradual transition from emerging mirror-reflected energy to diffusely dispersed energy is modeled. At the same time, the method takes into consideration certain acoustic characteristics of each section of enclosure such as sound attenuation coefficient and reflection coefficient. In the suggested form the method allows making calculations of noise in the buildings with any complex space-planning parameters.