Against the backdrop of intensifying global warming and the energy crisis, the imperative for green, low-carbon solutions presents new challenges for the energy sector, prompting nations and regions worldwide to enact and implement increasingly stringent building energy codes. These regulations drive the development of more efficient heating systems, where District Heating Networks (DHNs) play a pivotal role. The application of topology optimization to DHNs design is investigated in this study, aiming to minimize capital investment and enhance operational efficiency. We introduce the specific topology optimization framework employed and apply it to a real-world DHNs, demonstrating reductions of 1.3% in capital investment and 2.1% in operational costs compared to a conventional reference design based on expert engineering judgment. Furthermore, considering the project’s phased construction nature, we evaluated two distinct implementation strategies: findings reveal that neglecting long-term heat load projections during phased construction yields lower initial costs but incurs a 16.78% increase in total life-cycle cost, whereas pre-installing interfaces for future load expansion minimizes the total investment cost, representing the optimal overall construction scheme. This conclusion provides valuable guidance for designers in planning the phased development of heating networks, enabling optimal planning and design for such district heating projects.