The second death was on an extension to a warehouse in Bamber Bridge, Lancashire, for pharmaceutical firm Unichem.
Darren Brownbill, an employee of contractor Pochin, fell 12 m from the roof of the extension on Monday. He died later at the Royal Preston Hospital.
Both accidents are being investigated by the Health and Safety Executive.
Pochin managing director Anthony Pochin said in a statement: "All parties are assisting with the HSE's inquiries and our sympathies go out to Mr Brownbill's family and relatives."
The fatalities come a week after the HSE launched a campaign to reduce falls from heights. Six people have died in falls since the start of April.
The Don't Fall For It campaign was launched by a construction worker, Gary Weber, who survived a fall at the Four Seasons Hotel in central London in September 1999.
As part of the campaign more than 100 HSE inspectors will visit several thousand sites in the next two weeks to check safety precautions at heights.