Together with Kirstine Solberg he had the daughter Kaja Maartmann (1851–1933), who married Ellef Ringnes, brother of Amund Ringnes and founder of Ringnes Bryggeri. His son Harald Sigwart Maartmann (1855 - 1926) become the first director of Ringnes Bryggeri in 1901. He was the grandfather of Knud Maartmann Ringnes.
