The low-voltage (LV) distribution network has been largely excluded from detailed analytical consideration and as a consequence it is now the least understood and most unpredictable element of the electricity grid. Many advanced network control and optimisation methods require feeder parameters to be known in advance, and thus accurate low-voltage power network models are an important prerequisite. Smart meters, being the only reliable source of information in such networks, improve the affordability of low voltage automation infrastructure and allow for accurate measurements at almost every node. We propose a fully smart meter data driven method for line impedance calculations by iteratively solving a non-convex problem for each line. The performance of our algorithms is demonstrated for different measurement accuracy scenarios through simulations.