Laguna Presbyterian Church
Laguna Beach, CA

Remodel, addition and seismic retrofit to an existing 1920s church.  Since the church was constructed in the 1920s, it has under gone several remodels and additions, all without regard to its seismic stability.  The structures foundations are supported on substandard soils in a liquefaction zone due to a very high water table. 


To solve the soil conditions, a mat foundation was used without removal of the existing foundations.  The mat bridges out the building load over the entire footprint of the structure.  The projected seismic settlement was reduced from 19 inches to 0.6 inches.
The use of the mat slab eliminated the need for deep foundations allowing the existing foundation to remain in place.  This system significantly reduced construction cost. 

In addition, the rear of the church was shored and was excavated for additional basement area.  Concrete retaining walls and additional mat foundation slab was used for the new basement area. Plywood sheathing was added to the existing walls and roofs to create effective shear walls and diaphragms for the upgraded lateral system. 

Steel moment frames were installed within the bell tower walls to support the entry end of the structure laterally.  In order to install the steel, the upper most section of the bell tower, the cupola, was removed.  After the frames were completed, the rebuilt and reinforced cupola was reinstalled.