The Occupational Safety and Health Administration has sent three investigators to Little Egg Harbor Township.
OSHA spokeswoman Joanna Hawkins tells the Asbury Park Press the agency has up to six months to complete its investigation into what happened on Kansas Road on Wednesday.
Workers for ECO-Friendly Builders were jacking up the two-story structure that faces a lagoon so it would be above the flood zone when it collapsed.
Police said the most seriously injured worker suffered head and back injuries when he fell from the roof.
Information from: Asbury Park (N.J.) Press, http://www.app.com