The firm revised its reported loss from £5.8m to £12.7m in accounts formally lodged with Companies House last week.
Murphy said it uncovered additional financial losses on one project after an internal review process.
The firm blamed challenging market conditions and some difficult power projects in the UK, which have now been worked through and adequately provisioned.
Revenue at the business including joint ventures edged up 4% to £780m.
Of this around £71m was generated outside of the UK and Ireland.
After his first full year as chief executive, John Murphy said that the business continued to generate positive cashflow, ending the year with cash reserves of £63.3m (2017: £61.9m).
Murphy also renewed its £30m rolling credit facility with Lloyds in June.
The average number of staff at the business has reached almost 4,000.