The Sheffield-based group also said that its Return to Growth strategy is on course and the UK business has been rebuilt and relaunched. The firm said its reconnection with customers, suppliers and employees is now well advanced.
The firm said it has adapted successfully to trade safely within new Covid-19 norms, working closely and flexibly with employees, customers and suppliers.
Like-for-like sales fell 13 per cent in the year to December 31, with a solid recovery in the second half.
The firm reported an underlying operating loss of £53m, down from a £43m profit in 2019, which was an improvement on previous guidance.
The group made an underlying pre-tax loss of £76m, down from a profit of £18m in 2019.
SIG said its market fundamentals remain strong with good RMI (repair maintenance and improvement) growth in the UK and France.
Despite this, it warned that there is continued uncertainty over the Covid-19 pandemic.
However, it expects a return to profitability and cash generation in the second half of 2021.
SIG's chief executive, Steve Francis, said: "Our teams have shown great resilience and commitment in the face of the challenging circumstances for much of the year, the effects of which clearly impacted our first half, and hence full year, results.
"Providing a safe environment and instilling an even greater focus on good health and safety behaviours has been and will remain a major focus of the new management team.
"I am delighted that due to our Return to Growth strategy we delivered a solid second half and have begun to return the business to growth after a long period of decline. On behalf of the whole board I would like to thank all our employees for their significant efforts, and successes, during the year.
"The new UK management team has rebuilt its business and, everywhere we operate, we have reconnected with our employees, customers and suppliers. Their response has reaffirmed that we are at our best when we are a local, sales and technical service-driven business, partnering closely with our key suppliers and operating with empowered and entrepreneurial branch teams. That is our strategy for growth and the basis for playing a leading role in our industry in the years to come.
"This, coupled with a strong balance sheet, gives us the right foundations for the business to grow."