Completed in 1854, Old St. Mary’s Cathedral is one of the oldest red brick buildings in San Francisco. Located at California & Grant Streets on the edge of the Financial District, the church is San Francisco Landmark No. 2 as well as a State Historical Landmark. Old St. Mary’s served as the home of the Archdiocese of San Francisco from 1854 until 1891. For nearly two decades after it was built, Old St. Mary’s was the tallest building in California. It survived the 1906 earthquake, but only the outer walls and bell tower remained after the subsequent fires. The church was rebuilt in 1909 and enlarged in 1929. The church also survived the 1989 Loma Prieta earthquake with only a few structural cracks in the bell tower, but as an unreinforced masonry building it was not up to current seismic code required by state law. Providing the archdiocese with a cost-effective solution to preserving the church was vital.
For Phase I, Nibbi Brothers provided seismic upgrade work which included new structural steel cores which extend into the attic, new foundation concrete in the basement and new structural concrete walls in the auditorium. The main shear cores are composed of structural steel and shotcrete and will be epoxy dowelled to the exterior of the church. Additional work included re-roofing, upgrades at the altar and pews for ADA compliance, re-painting the interior and installing new fire sprinkler service.
In Phase II of the project, seismic upgrades to the church’s clock bell tower were completed. This included a shoring and underpinning package under the south wall. Two large cast-in-place concrete buttresses were installed under the existing entry stairs to the cathedral. The inside of the tower was completely gutted, and the existing brick walls were roughened by a bushing hammer to an amplitude of 1/4” roughness. This allows the new shotcrete walls to adhere to the existing brick masonry. A double curtain rebar matt was fabricated at all 4 interior walls, the entire height of the tower and a new HVAC system was installed at the attic level for the Cathedral’s heating and venting.
Since Old St. Mary’s was a working, active parish, it was vital that it was kept open during construction. The pastor, Reverend Charles Kullmann worked closely with Nibbi Brothers to coordinate schedules and avoid any parish disruptions. With that in mind, the schedule dictated that the workers stop any construction that would cause noise or be a safety issue twice a day, from 7:30-8:00am and from 12:00-12:30, so that mass could be conducted. Work stoppage was also sometimes necessary for funerals or weddings held at the church.