SAN FRANCISCO—Workers compensation is the exclusive remedy for a construction foreman who was injured while working on his boss's house, a California appellate court ruled this week.

Charles DeFrates sought to sue Robert Clark, sole owner of R.G. Clark Construction Inc. in Calpella, Calif., for personal injury after he slipped and fell while working on the roof of Mr. Clark's new duplex, court records show.

In an unpublished opinion Tuesday, the California Court of Appeal said Mr. Clark can't be held personally liable for Mr. DeFrates' injuries because he was acting as Mr. DeFrates' employer, rather than a client, when the accident occurred.

"DeFrates put forward no evidence, much less undisputed evidence, that Clark acted with regard to safety matters in an independent capacity rather than as DeFrates' employer," the ruling reads.

Mr. Clark hired his own construction firm to build a new townhouse for himself in 2006. Months later, Mr. DeFrates was instructed by Mr. Clark to build scaffolding to protect company employees while working on the home's roof.

Mr. DeFrates claimed there was not enough material to build a safe scaffold, and asked Mr. Clark to provide roof jacks instead for the project. Mr. Clark declined, and soon afterward, Mr. DeFrates fell off of the home's roof.

Mr. DeFrates received workers comp for his injuries, though he returned to work "a day or two" after the accident, records show.

Mr. DeFrates argued that Mr. Clark was acting on his own behalf when he chose not to provide roof jacks. But the appellate court said Mr. Clark was acting as an employer when he told employees to work without those materials.

"The only undisputed evidence...directly relevant on this point is that Clark gave safety instructions to his 'employees,' and was the 'representative of the employer R.G. Clark Construction,'" the ruling reads.

The court also said Mr. Clark isn't personally liable because R.G. Clark employees never used the scaffolding materials that he provided.

"Clark did not worsen DeFrates' position by providing the scaffolding," the opinion said. "In fact, to the extent Clark was operating as a hirer, he had no duty to provide any safety equipment to the employees."