Chief executive Paul Cossell said the group was well placed to meet the covid-19 challenge and warned that he expected revenue between March and June to fall by 25%.
Like other contractors, ISG has implemented pay cuts among the highest-paid and furloughed staff.
Cossell said: “Covid 19 creates uncertainty for the remainder of the financial year, but the board has further cash preserving measures that it is willing to implement if appropriate, recognising that maintaining our dedicated and talented people is a key priority in anticipation of the increased volume of work in 2021.”
Last year ISG lifted underlying profit by over a third to £52m on revenue ahead 15% at £2.6bn.
This left ISG with net cash of £117m, up from £74m in 2018.
The pre-tax figure was depressed by £8m to £44m after exceptional costs closing ISG’s Brazilian business.
ISG achieved its target of 2% net operating margin in 2019, and entered 2020 with a forward order book of £1.4bn.
Profit growth was driven by the engineering services business, which focuses on data centre and complex science and healthcare work. It more than doubled profit to £25m on revenue ahead 65% to nearly £800m.
The firm’s fit-out business had a stable year delivering a small uplift in profit to £23m on stable revenue of £1.2bn.
The construction arm saw profit slip from £5.7m to £4.4m over the year on revenue ahead 8% at £520m.
Cossell said: “As we look to 2020 and what promises to be a year of unknowns, I am confident in our continued strength.
“Even with Covid 19, we will work to set strong foundations for future growth.”