The Chrysler Building, St. Patrick’s Cathedral, and the Manhattan Municipal Building are among the structures Kent Diebolt and his team have dangled from on ropes the width of pinkie fingers. Unlike those who recently climbed the New York Times building, Mr. Diebolt’s actions are perfectly legal: He is president of New York-based Vertical Access, a company of engineers doubling as rock climbers who scale skyscrapers and historic buildings to verify that they are sound.

This fall, the 16-year-old company will install a cable around the perimeter of the New York Public Library’s roof, allowing the building’s workers to clean safely the leaves and shopping bags that clog the gutters.

Vertical Access is one of a handful of companies in New York City that uses the so-called industrial rope access method, in which employees rely on a double-rope system, similar to that used by rock climbers, to inspect and document the condition of buildings. For tall buildings, scaffolding is often too difficult to erect, and industrial rope access offers a less expensive alternative to using a crane.

“If you’re in the middle of a building façade, you have a lot of building around you. If you’re on a spire, you have nothing around you except air,” Mr. Diebolt, 55, said.

The six-person company completes some 30 projects a year. The firm has two offices: one in Ithaca, where Mr. Diebolt and his wife raise their three children, and another in Manhattan, near Union Square.

The majority of Vertical Access’s work is on pre-war buildings, which are more difficult to inspect than modern buildings. Because of their historic status, and New York’s stringent standards for landmark buildings, there is often an arduous process involved in applying for permits to inspect the buildings and conduct any work.

“New York City is more regulated than other cities,” Mr. Diebolt said. “We have to get permits to do this kind of work in New York City and we don’t anywhere else.”

Perhaps the most difficult of his projects took place following the terrorist attacks of September 11, 2001. Two days before the attacks, the company finished inspecting the façade of Trinity Centre, two 22-story office towers a block from the World Trade Center. After the attack, Vertical Access returned to Lower Manhattan to assess the disaster’s impact on the buildings. While there was minimal lasting damage, it was heart-wrenching work.

“Being in the shadows of those buildings in the months before September 11, and then suddenly, they’re gone, it was horrifying,” Mr. Diebolt said.

Mr. Diebolt was running his own construction company in Ithaca in 1991 when he first grew interested in industrial rope access. A rock climber friend helped him with some rigging on a job, and later introduced Mr. Diebolt to the owner of Skyline, a rope access firm based in England. Mr. Diebolt visited England and worked alongside Skyline’s operators, inspecting buildings in Brighton before returning to New York and registering his own rope access company a few months later.

While Vertical Access has competition stateside for business, the bulk of companies that use industrial rope access to inspect buildings are based in Europe. One of the largest is the CAN Group, headquartered in Aberdeen, Scotland, which operates in more than 40 countries and has more than 1,000 employees. Past projects include the inspection of concrete nuclear reactor domes and offshore oil rigs.

The CAN Group has an office in New Jersey, and works regularly in New York City. Among its recent jobs was the installation of lights on the Coney Island Parachute Jump, and hanging façade netting on the New York Public Library. Despite the close proximity of their work, the CAN Group says Vertical Access isn’t a direct competitor. “They have a different focus than us,” an operations manager at the CAN Group, Timothy Barry, said. “They do more high-end engineering and historical restoration, whereas we do more labor and documentation.”