PORTRLAND, Maine — The state has signed off on Maine Medical Center’s $512 million expansion that stands to become the largest ever undertaken by the hospital.

The Maine Department of Health and Human Services this week blessed the project by granting a Certificate of Need.

Richard Petersen, Maine Med’s president, said the expansion and modernization will “provide the best possible care for our patients.”

The project, to be completed by 2022, will add single-patient rooms and 20 operating rooms, but the total number of beds will remain unchanged at 637.

Currently the hospital has 303 double-occupancy rooms, which Maine Med officials say is no longer the standard of care.