Cathedral School for Boys


The Cathedral School for Boys sits at the uppermost corner of the landmarked Grace Cathedral Close block, adjacent to the apse end of the Cathedral. The two-story addition designed by our office is connected horizontally to the original 1960s school building and sits on top of an existing concrete expansion from 2009. Our design consists of a steel structure with a glass and aluminum curtain wall: the new addition was light enough to land on the existing structure without foundation upgrades, and construction was sequenced to avoid interrupting the academic calendar. The addition contains open common spaces for large gatherings, small meetings, and quiet study, with spectacular views of the Cathedral transept and the downtown skyline. The project also included an interior renovation that created a new entry axis, leading directly from the front door to the new heart of school life.


Cathedral School for Boys

4,500 SF (addition)
18,000 SF (renovation)

1275 Sacramento Street, San Francisco
“Charles F. Bloszies inserts glass addition into San Francisco Cathedral Complex,” Kate Mazade, Dezeen, February 8, 2023

“How to Expand Urban Schools Creatively and Efficiently,” Jenelle Penny, Buildings Magazine, September 25, 2023


Over the last half century, the school has expanded multiple times into adjacent buildings, and even into the Cathedral itself: the cafeteria, gym, and performance spaces are in the crypt. The school’s strategic plan had identified the need for additional space to accommodate contemporary learning practices, as well as space for large student and community gatherings. Since the block had been so thoroughly developed, there were limited options for situating this new space. The location that was ultimately selected was the narrow slot between the school and the Cathedral, on a terrace comprised of the roof of an earlier addition.

The additioin is located deep within the Grace Cathedral block, far from the school’s primary entrance on Sacramento Street and surrounded by existing buildings. This posed a challenge: how can the new spaces be connected to the old in a way that allows them to be a hub of activity?

The connection to the new “heart” was made by rearranging the classrooms as part of their renovation to allow for a grand entrance leading directly from the Sacramento Street doors to the new “Learning Commons,” terminating in a striking view of the Cathedral complex that opens up into the panoramas afforded by the floor-to-ceiling windows.

One of the project’s greatest successes was the construction schedule. The classrooms were completely renovated during the three-month summer break, along with the disruptive structural work to frame the new addition. A temporary barrier was erected between the classrooms and the addition shell so it could be finished while school was in session during the fall term. The curtain wall was prefabricated off-site in panels that were craned into place in a matter of days. The project was completed over winter break, and ready for students when they returned for the spring semester.

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Copyright: Office of Charles F. Bloszies, 2024