Resignations by Fletcher Construction's two top players can be traced back to a single project.

The company has reported a $120 million half-year loss after tax.

Chief Executive Ross Taylor and Chair Bruce Hassall have announced they'll both leave this year.

Taylor says remediation for the SkyCity fire in 2019 was the most complicated thing he's seen in 40 years in the industry.

"We basically progressively only understood what we were up against- and then we had to re-forecast. In the end, I think the team's done a great job to keep it on track, program wise, and we really couldn't forecast until we worked out how to do this stuff."

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