The Golden Gate Bridge

Conservatory of Flowers

Structural Engineer Nancy Tennebaum and her team at Tennebaum-Manheim Engineers used a green, sustainable solution reclaimed old growth redwood to restore and retrofit San Francisco's historic Conservatory of Flowers in Golden Gate Park.

It all began in December 1995, when a particularly harsh storm hit San Francisco. The City was forced to close the Conservatory and seek help in restoring one of its rare treasures. Between 1997 and 2003, the Structural Engineers led a $25 million project, which included seismically upgrading the structure to code, repairing rotted and wind-damaged elements and preserving the historic fabric without intruding on the architecture.

The Conservatory of Flowers, originally completed in 1878, survived the 1906 earthquake and today is the oldest building in San Francisco's Golden Gate Park. It is also the oldest remaining wood and glass greenhouse in the United States. This is one of the achievements of the Structural Engineers, who used innovative retrofits to strengthen the structure, preserve its delicate façade, and remain true to the original material by using reclaimed old-growth redwood.

The Conservatory was completely disassembled and rebuilt with lateral strengthening techniques to help it survive future earthquakes. New steel and wood elements helped maintain the structure's delicate quality. Also included were a new foundation, a new system of concealed stainless steel reinforcement plates and exposed steel trusses with three-quarter-inch diameter cross bracing rods that complement the lightness of the building. All clear glazing was replaced with laminated safety glass.

Rebuilt from the ground up with a combination of wood and steel elements

The structure has a domed pavilion at its center that is roughly 55 by 55 feet in plan and 68 feet tall. In order to meet the quick construction deadline, the Structural Engineers constructed the dome on the ground and then lifted it to its final position. Two symmetrical L-shaped wings flank the dome room. The wings and dome are made of a series of wood arches, in which the arches are assemblies of several pieces of wood connected with elegant scarf joints.

The beautiful domed pavilion rising to a height of 68 feet

The simple decision to use redwood frames became complicated in order to comply with a City of San Francisco ordinance that prohibited the use of virgin redwood products. Therefore a "green" sustainable solution resulted in the use of reclaimed old-growth redwood for structural arches for the Conservatory of Flowers. Each piece of wood was hand graded, allowed to dry for 30 to 60 days. Samples were tested for structural strength and durability before being accepted.

Every city has its architectural gems. As a result of the Structural Engineers' efforts, few return visitors to the Conservatory will notice the structural changes to this beloved, seismically renovated beauty.