The case is understood to be the first successfully prosecuted case of industrial manslaughter in NSW.

Roof plumber David Peter Smith, of Speers Point, originally pleaded not guilty to manslaughter, and the matter was to go to trial. He changed his plea yesterday in Newcastle District Court.

Edgeworth mother Judith Davis, 41, Smith's former partner, fell 9.6 metres through a roof to her death on the morning of April 25, 2003.

An agreed statement of facts tendered to the court said Smith, who ran his own business, David Smith Roofing and Guttering, was contracted to strip and re-sheet the roof of an industrial building at Abdon Close.

The relatively flat roof was mostly metal, but some portions had translucent polycarbonate sections to improve lighting, which were less strong. Under these sections, wire mesh was rolled out as a safety measure.

Ms Davis was walking across the roof about 8am and stepped onto a sheet of polycarbonate near the ridgeline of the roof, which, along with the safety mesh beneath, gave way. She fell onto a concrete floor below and suffered head injuries.

An examination of the mesh showed it was not attached to the roof in either of two ways approved in a code of practice.

Smith gave evidence yesterday that he was not at the site when the mesh was installed and should have checked that his workers had done it properly.

He told the court he and Ms Davis had been in a 14-year relationship but had been estranged for a number of weeks when the incident occurred.

"I didn't regard her as an employee," Smith said.

"I regarded us as a partnership . . . we were life partners," he said.

An emotional Smith told the court he had since lost his business and his home, as well as his relationship with Ms Davis's children.

The hearing continues today.