Curators are putting
finishing touches on exhibits at San Franciscos Conservatory
of Flowers, following a $25-million restoration that involved
almost complete disassembly and reconstruction.
Erected in Golden Gate Park in
1879, the city-owned Victorian-era greenhouse is the oldest
public conservatory in the Western Hemisphere, but it has
been closed since a fierce winter windstorm ripped through
the 12,000-sq-ft redwood and glass structure in 1995.
speed palm room reconstruction, the contractor built the
upper portion of the dome on the ground and lifted it
into place. (This photo and above courtesy of the Conservatory
of the Flowers)
The storm shattered 40% of the
glazing, damaged some of the structural components and destroyed
a portion of the collection of rare tropical plants. But inspection
of the building revealed that the conservatory had been deteriorating
for years, exacerbated by a series of modifications and high
humidity. Much of the wood was like "Swiss cheese," says Deborah
Cooper, project manager for locally based design and conservation
firm Architectural Resources Group.
The decay came from many sources.
Use of iron nails to join wood components in the original
construction had caused ferric degradation of the wood around
the nails from an acidic reaction. During a 1959 renovation,
operable windows used for ventilation were filled in, contributing
to excessively humid conditions inside the building. In the
1970s, some redwood was replaced with laminated members. The
glue "just turned to mush" in the greenhouse environment,
says Nancy Tennebaum, principal of San Francisco-based structural
engineer Tennebaum-Manheim Engineers.
conservatory's oldest and largest specimens required temporary
enclosure during the Palm Room restoration. (This photo
and bottom by Joann Gonchar for ENR)
The structure has a domed pavilion
at its center that is roughly 55 x 55 ft in plan and 68 ft
tall. The pavilion, or palm room, is flanked by two symmetrical
L-shaped wings, approximately 19 ft tall and 35 ft wide. The
wings are made of a series of wood arches, roughly 7 ft, 6
in. on center, connected by purlins at three points on each
One of the chief challenges facing
the design and construction team was selecting the material
for replacement of the deteriorated redwood components. This
was complicated by a city ordinance prohibiting the use of
old-growth redwood. The team considered aluminum. But this
likely would have meant losing the buildings landmark
status. Pressure-treated young-growth redwood was another
option. However, the pressure treatment and drying process
would have required between three and six months.
arches and purlins wre milled from redwood "buckskin"
Eventually the team decided to
use redwood "buckskin" logsold-growth trees that fall
naturally or are standing stumps abandoned by loggers. The
buckskins were considered the "most historically correct and
the most durable option," says Edgar Lopez, project manager
for the Dept. of Public Works.
The city assembled its own team
to find and collect the buckskins and it supplied the wood
to the contractor. Each piece was hand graded and tested for
density and structural integrity after drying from 30 to 60
days and before milling to the sizes and shapes required.
"Since the strength of the material was not known, we had
to develop our own [testing] program," says Tennebaum.
One of the most logistically complex
parts of the project was reconstruction of the palm room.
The pavilions exhibits include a 35-ft-tall imperial
philodendron and a 20-ft-tall pygmy date palm, both about
100 years old. The plants are among the oldest and largest
in the collection and could not be relocated for construction.
To work around them, the contractor, ISEC Construction Services,
Davis, Calif., devised a temporary enclosure supported by
scaffolding, complete with irrigation and climate-control
To speed construction, the contractor
built the top portion of the dome on the ground and then lifted
it into place by crane. "Constructing the dome in the air
would have taken us twice as long," says Ken Zad, general
superintendent for ISEC.
Since the dome forms a triangle,
"it has great stability," says Tennebaum. Still, the 29,000-lb
lift was nerve-wracking for the contractor, who lifted it
from four points inside the structure. "But once we got if
off the ground we could see that it wasnt deflecting
or moving," says Zad.