Rehabilitation of Crissy Field Airplane Hangar

^{Presidio Building 643, located on Crissy Field. NPS}

Crissy Field Air Reserve Hangar (Presidio Building 643)

In 1921, the U.S. Army established the Crissy Field Air Service Coast Defense Station as the only military airfield on the west coast specifically built as a coast defense air station. The Crissy Field pilots of the 91st Observation Squadron provided assistance to the on-the-ground Coast Artillery soldiers by flying overhead, spotting and ensuring the batteries’ fire and target practice. The military airplane hangars, such as Building 643, offered large protected spaces for plane storage and maintenance. Constructed in 1923, Building 643 was originally two, separate steel frame and corrugated steel-clad hangars. The military used each building as an Air Reserve hangar, with a capacity to store up to 16 planes. To help pilots locate the landing strip in Crissy Field’s legendary dense fog, the army painted “CRISSY” and “FIELD” on the building’s individual roofs.

^{This early photo shows the two distinct hangar buildings, covered with original metal exterior siding and painted “Crissy” “Field” to guide the pilots safely home (circa 1920s). National Archives}

By the mid-1930s, Crissy Field was discontinued as an active airfield. As the army no longer needed the big open hangar space for airplane maintenance, they converted Building 623 into a post engineer shop and constructed many interior partition walls to create drafting rooms and clerks’ offices. After Building 643 experienced a damaging fire in 1940, the army made significant repairs. To shore up the interior partitions, the army used hollow clay tiles, which was a then popular cement building material. They constructed a wood-frame office addition that physically linked the two hangars and replaced the buildings’ original corrugated metal exterior walls with hollow clay tile. They re-clad the whole building with a cement plaster and added the Mission Style parapets at the middle, east and west ends.


^{This oblique view shows Building 640’s corrugated metal siding and the large industrial doors (circa 1920s).}

 

The Rehabilitation of a Historic Airplane Hangar

 

The existing hollow clay tile is fragile and prone to deterioration. NPS

The National Park Service rehabilitated the 20,000 square feet building into a park maintenance facility housing the park’s sign shop and carpenter shop, offices for the park’s buildings and grounds maintenance staff, as well as storage for the park’s equipment and vehicles. Because the building contained hollow clay tiles, the National Park Service had to address some remodeling challenges unique to San Francisco - a place that experiences seismic activity (“seismic” refers to earthquakes or earth vibrations). Current California state building codes ensure that every new building is constructed and seismically reinforced to withstand an earthquake. But there were no seismic building codes back in the 1923 when the army constructed Building 643.

Building 643 faced many structural challenges, making it vulnerable to significant damage during an earthquake. The first challenge is that the building was constructed on land fill. Up through the 19th century, Crissy Field was once a very large wetland area. In 1915, the City of San Francisco identified this large and undeveloped, watery space as the perfect location for the city’s forthcoming world fair. They leased the space from the Presidio army, poured an enormous amount of dirt and soil into the wetland and created land to host the Panama-Pacific International Exposition. Unlike bed rock, landfill can move quite significantly during an earthquake; buildings built on landfill are more likely to sway and experience damage.

The building’s second structural challenge was the hollow clay tile building material that exists in the interior and exterior walls. Unfortunately, hollow clay tile is a brittle cinder block that break easily under pressure and performs very poorly in an earthquake environment. To ensure that the building is seismically reinforced, the National Park Service removed all the hollow clay tiles and built new lightweight interior steel frame walls that can easily withstand the structural load during an earthquake. The exterior was stuccoed to replicate the historic appearance.

Building 643 contains more than 45 historic steel frame and glass windows that have been badly damaged by the harsh Crissy Field marine environment. After a thorough inventory, the National Park Service determined that the existing steel windows were too far deteriorated to repair and would replace the historic windows in-kind. The National Park Service created a Steel Window Preservation Guide (this document is available by emailing us) to provide guidance on the best way to preserve and protect this building element.


^{Building 643’s historic steel windows are significantly deteriorated. NPS}