Currently, the digitalization of construction projects is becoming a reality. The energy model of a build-ing (BEM) is being introduced into the design practice, which does not allow directly solving the prob-lems of designing engineering systems of a building. There is a gap in approaches to building a digital building information model. On the one hand, there is the maximum use of information from the digital model during design calculations. On the other hand, there is a simplification of mathematical models for solving problems related to the design of engineering systems. Many important tasks of design and op-eration of engineering systems are not solved in conjunction with the premises of the building. It is pro-posed to use the representation of the building as a graph, which will allow you to solve the problems of design and operation of engineering systems correctly. Most of the necessary information is already pre-sent in the building information model and can be extracted from it automatically. As an example of con-verting information from a digital model, the problem of determining the heat loss of premises was cho-sen. This task is a mandatory part of any project. Existing software products do not allow you to automat-ically determine the dimensions of the enclosing structures of the room that are necessary for solving the problem, and do not take into account the relative location of the premises. These reasons determine the need to develop the application. Materials and methods: To solve the problems of design and operation of engineering systems of a building, it is proposed to use a topological model of a building, which is a connected graph, the compo-nents of which are a base subgraph describing the connections between the premises of the building and subgraphs of engineering systems. The data structure and algorithm for forming a basic building sub-graph based on a digital building model are presented Results: The software application that implements the proposed algorithm was tested on the calculation of heat loss in the premises of a building. A 3D model of a 10-storey residential building was used as the object of the experiment. As a result of the experiment, a reduction in the time required for the prepara-tion of the initial information and for the calculation was revealed from 8 hours to 20 minutes.. Conclusions: Taking into account the relative location of building premises and life support systems in the topological model of the building allows solving problems of environmental and fire safety, optimiz-ing design solutions for supply, exhaust, smoke ventilation systems and other tasks. The developed soft-ware module designed for calculating the heat loss of premises is the first step in the development of software products that use a digital model of a building as the initial information for building a topologi-cal model.