Flowers for San Francisco
Traditional Building Magazine – Oct. 2005

By: Hadiya Strasberg

Project: Conservatory of Flowers, San Francisco, CA

Architect: Architectural Resources Group, San Francisco, CA; Bruce D. Judd, FAIA, Principal;
Deborah J. Cooper, AIA, Project Manager; Andrew Blyholder, Project Architect
Structural Engineers: Tennenbaum-Manheim Engineers, San Francisco, CA

Traditional Building MagazineThough it’s not the oldest structure in San Francisco, the Conservatory of Flowers is the oldest structure in Golden Gate Park and the oldest public greenhouse in California. The building was threatened in 1995 when a series of storms damaged the 1879 structure and it was closed to the public. Two years ago, in September of 2003-after an extensive $25 million, eight-year rehabilitation project that involved the disassembly and reconstruction of the structure, lead abatement and seismic strengthening-the conservatory was reopened.

The 12,000-sq.ft. building-constructed of 100 old-growth California redwood arches, old-growth redwood ornament, either cast-iron columns, Douglas fir purlins, sugar maple mullions and 16,800 glass window panes-has an elusive history. It is clear that a group of San Francisco businessmen purchased the conservatory from a real estate magnate in San Jose and donated it to Golden Gate Park in 1878. However, while it is known that Irvington, NY-based Lord & Burnham assembled the structure in the park, there is only speculation as to the identity of the designer.

When Architectural Resources Group (ARG) and Tennenbaum-Manheim Engineers (TME), both of San Francisco, became involved with the project in 1996, the reconstruction work that lay ahead was daunting. Structural damage was extensive, with the south and west elevations most badly affected. More than 20% of the conservatory’s glass windows were destroyed and several redwood arches were broken.

Window RestorationThe conservatory was not the only thing damaged by the storms. Tropical plants from 53 countries had been housed in the building, a number of which were destroyed. “A collection of plants was damaged by shattered glass,” Bruce Judd, FAIA, principal architect at ARG, describes. One of the first matters tackled was relocating the plants. ARG and TME worked with the city’s contractor, ISEC Inc./Troy’s Contracting, to install a prefabricated temporary greenhouse. “Some of the plants couldn’t be moved, because their root systems had attached themselves to the building,” says Deborah Cooper, AIA, ARG’s project manager. “We created a support structure for those plants and built mini-greenhouses around them, complete with heating, ventilation, and misting systems.” During the first phase of the restoration, four team members wore pagers that would alert them to a drop in temperature below 58 degrees, which thankfully never happened.

Aside from the storms’ impact, years of neglected maintenance and some unsympathetic renovations done 30 and 50 years ago had left the wood structural members badly deteriorated. “When we surveyed the building, checking the wood for deterioration at 1-ft. intervals” says Cooper, “we found that the deterioration was very severe on the sills and the bases of all of the arches that sat on the sills.” Judd explains, “Iron nails had caused ferric degradation of the wood. The closed lower ventilation windows, which had been filled in with concrete in the 1950s in an effort to simplify maintenance, locked moisture in the building and caused the wood to rot.” While the upper vents had not been sealed, they were found in a deteriorated state and no longer operable, because they had absorbed so much moisture over the years.

Another unsympathetic change, this one from a ’70s renovation project, was the removal of copper flashing around the windows, resulting in leaks. The combination of these unsympathetic renovations and deferred maintenance resulted in very severe deterioration of the wood members.

One of the reasons the conservatory had not been properly maintained was a lack of funds. In order to address the more drastic ruin, a fund-raising effort run by Friends of Recreation and Parks and the San Francisco Garden Club was launched. Millions of dollars were raised in a relatively short time. “The ’95 storms brought the conservatory to the public’s attention,” says Judd. “It actually allowed us to do work that had been neglected for years”.

Reconstructing the Conservatory of Flowers brought up a host of dilemmas. Since the original drawings no longer existed, ARG and TME had to discover how the structure was put together. The firms decided to conduct a test run, in which they “took apart and then reconstructed 450 sq.ft. of the west wing, carefully documenting the entire process,” says Judd. “Since we would need to work around five large plants that couldn’t be moved to the temporary conservatory, we re-created that condition in our test run, bringing in flora to make sure our reconstruction system worked.” The plants were covered in heavy-duty plastic and were temperature and humidity controlled. “We only killed the first test tree,” Judd says.

Window Restoration ExteriorThe next predicament was choosing materials to replace those that were damaged and structurally unsound. ARG reused as many mullions and as much ornament as was salvageable, about one-third of the original redwood, but needed approximately 2,000 replacement pieces. This included all of the arches and purlins. “We considered using new pressure-treated redwood, but opted for reclaimed, old-growth redwood that came from stumps of trees that had been previously cut at 30 ft. tall, because it was a more environmentally conscious and historically accurate material to use.” A subcontractor hand-graded each piece to determine its structural integrity.

The restoration of the central dome brought up another question of historical accuracy, namely which dome to reconstruct. After a fire in 1893, the original dome had been destroyed and a new one designed and constructed in its place. “There are early photographs of the conservatory as well as extensive written histories of the building,” says Judd. “From these sources, we know that the dome of 1893 was taller than the original.” Without plans of the original dome’s specifications, though, ARG and TME decided to retain the newer design, which was 68 ft. tall. “The main challenge concerning the dome was the seismic bracing,” says Judd. “It was hard to keep it from spreading and falling apart, but TME came up with a wonderful solution.” The dome’s wood skeleton was disassembled and, on the ground, a number of stainless-steel pieces and tension rods were installed to strengthen the dome. “One of the most gratifying moments of this project was when the re-constructed dome was picked up by a crane and set on the building,” says Cooper.

The stainless-steel reinforcement plates used to strengthen the dome were actually hidden throughout the conservatory’s wood structure to meet the current building codes, including a new foundation and exposed steel trusses with ¾-in.-diameter cross-bracing rods. Laminated safety glass replaced the standard clear glazing in all of the building; some original interior colored glazing in the clerestories was preserved. “A glass restoration specialist found more than a dozen different kinds of glass in the conservatory-very little of it original,” says Cooper. “Presumably, as the glass broke, it was replaced with whatever was on hand.”

To meet ADA regulations, ARG created a series of gently sloping walkways. “We designed sloping walkways instead of ramps with handrails to maintain the same type of aesthetic originally designed,” says Cooper.

Mechanical and electrical systems were also updated throughout the restored structure. A heating system that ran under planter benches around the conservatory was replaced with trenches down the centers of the walkways in which were run all of the heating, electrical, water and data lines. In-ground planters replaced all of the planter benches. A new HVAC system was installed. Air Separator Installation was also carried out so that the HVAC system runs more reliably and cost-effectively. As well as this, a computer system that controls the temperature and humidity in each of the five main spaces in the conservatory was added.

The restoration of the Conservatory of Flowers was a joint effort, one that Judd commends. “We worked very well together,” he says. “It was a very complicated project, because we had to make sure that the contractors and subcontractors were meeting historic preservation standards, but it turned out that I had nothing to worry about. The people with whom we worked were excellent. It was a very good process.” The result of eight years of collective effort won the conservatory the Governor’s Historic Preservation Award for 2004, the AIA National and Local Honor Awards for Architecture in 2005 and the California Preservation Foundation Preservation Design Award for Rehabilitation for 2005.