California school construction projects built under contracts containing project labor agreements cost 13 to 15 percent more than those projects built without such agreements, according to a study released July 25 by the National University System Institute for Policy Research in San Diego.

PLAs are agreements between contractors and construction trade unions that address hiring preferences, wages, benefits and how labor disputes are to be resolved.

Presently, 24 kindergarten to 12th grade school districts in the state, including the San Diego Unified School District, have adopted PLA provisions.

The study found between 1996 and 2008, the districts with PLAs built 65 schools for a cumulative cost of $9.7 billion. Using data for schools built without PLAs, the study found schools built under the agreements cost about $200 million more.

In inflation-adjusted dollars, the study said projects built under a PLA increased per-square-foot costs by $28.90 to $32.49.

— Mike Allen