Energy conservation and network longevity are key requirements of Internet of things (IoT) applications. However, these can be challenging in indoor environments such as dwellings with reinforced concrete walls and highbay areas using battery-powered wireless devices. This paper presents a low-power power line communication over IPv6 network (6LoPLC) for in-building IoT applications. 6LoPLC adopts a PLC physical layer (PHY) and exploits media access control (MAC) features of IEEE 802.15.4 devices as well as 6LoWPAN to deliver low-power, low rate PLC. One of the unique advantages of 6LoPLC is that the nodes are mainsconnected which eliminates the network disruption caused by battery depletion in wireless nodes. Furthermore, 6LoPLC saves the time and effort on battery recharge or replacement, simplifies network management and reduces wiring cost. The results reveal that the proposed system can yield about 5.05 dB reduction in energy requirement relative to HomePlug Green PHY without violating the delay tolerance of the IoT applications. It is further shown that using the 6LoPLC technique, delays of about 48 ms and 129 ms are feasible in residential and commercial buildings respectively. Index Terms-6LoPLC, building area network (BAN), smart city, smart home, Internet of things (IoT), power line communication (PLC).