Construction programmes on mainly fixed price contracts were hit by record levels of supply chain inflation, the directors said in their annual accounts.
The company has taken steps to restructure its UK South operations and expects to see it return to profit this year. Former Kier chief operating officer Steve Bowcott was brought in as managing director in July 2015 in place of Gary Crabtree.
Turnover for the year ended 31st December 2015 was £419.4m (2014: £343.8m). The £17.8m pre-tax loss for 2015 compares to an £859,000 profit in 2014. At year-end Sisk had net liabilities of £4.56m.