Roper Berta de Miguel takes pictures while inspecting the Municipal Building in Manhattan. Adrienne Grunwald for The Wall Street Journal

Dangling from ropes, Berta de Miguel looks perfectly at ease climbing high on the exterior of Manhattan's Municipal Building, a 40-story structure across the street from City Hall.

But even while hanging more than 500 feet above ground, she isn't a daredevil—she is an architect and skilled rock climber surveying the landmark building's aging facade.

"As a human being up this high, it is natural to be nervous but when I'm on the rope, I'm not nervous," said Ms. de Miguel, her waist in an apparatus that connects to sturdy ropes.

Ms. de Miguel, 31 years old, is part of a team of professional ropers with Vertical Access LLC, a company commissioned by engineers and architects to survey the exteriors of usually-tall buildings throughout New York City.

Checking buildings while hanging from ropes is considered an efficient way to examine trouble spots and is often a more cost-effective first step than scaffolding, although that is frequently needed later for construction work and repairs.

She makes her way down the facade. Adrienne Grunwald for The Wall Street Journal

"I wish I was Spider-Man and could just climb up a building and look at something. Of course, I can't but this is the closest thing to it," said Robert Silman of Robert Silman Associates, an engineering company with offices in New York that has hired Vertical Access for work on the Cathedral of St. John the Divine, St. Patrick's Cathedral and the Thurgood Marshall U.S. Courthouse in lower Manhattan.

"You can crane your head out a window, you can use binoculars, but it's not the same thing as being inches away from something that may be a hairline crack or confirm there is not a crack," said Mr. Silman.

Kent Diebolt, 61, started Vertical Access in Ithaca, N.Y., in 1992, after using ropes to inspect buildings in England. Even though he was "scared to death" with the work initially, the Cornell University-educated contractor loves being up close to the skin of a building, particularly in New York City with all its historic structures.

"They are some of the last handmade buildings in the U.S. and they were beautifully made," he said.

Vertical Access is now a nine-person company, or "industrial rope-access workers," as Mr. Diebolt calls them. He said the company hasn't had an injury except for an elbow cut on a piece of razor wire.

Richard Pieper, director of preservation at Jan Hird Pokorny Associates in Midtown, hired Vertical Access to check out conditions on the New Jersey State House and the Enid A. Haupt Conservatory at the Bronx Botanical Garden.

"You can't erect a scaffold for every inspection you do—it's simply too expensive and owners don't want them [view obstructions] up unnecessarily," Mr. Pieper said.

Vertical Access ropers are armed with tablet computers that allow them to video stream what they are seeing to architects or engineers in real time. An architect may direct them where to move or to clarify if something is a shadow or a crack.

Ropers also videotape and photograph conditions for clients, providing them with data to determine how and when to proceed with later construction work.

The cost savings using ropes can be substantial. The inspection of Manhattan's Municipal Building, for instance, was slated for $1 million using scaffolding, but Vertical Access did it for $85,000, according to Vikrant Sampat of Superstructures, a Manhattan firm hired by the city to report on conditions of the building's facade.

"Basically, we were saving $915,000 by using Vertical Access. It made sense," said Mr. Sampat, who also noted the shape of the building made it difficult to erect scaffolding.

With early skyscrapers now more than 100 years old and increasingly subject to problems, demand for exterior inspection services has been growing. Even so, building owners have long relied on using cherry pickers, leaning out of windows, scaffolds and binoculars to inspect conditions. Because of unfamiliarity or the absence of formal training for the specialized trade, architectural firms often were reluctant to hire ropers.

A rope and equipment harness used by workers for Vertical Access. Adrienne Grunwald for The Wall Street Journal

That has changed in the last decade as the roping field has become safer and more accepted, according to Loui McCurley, a founding member of the Society of Professional Rope Access Technicians in Wayne, Pa. She says the group's membership has doubled in the last five years to 112.

The city Department of Buildings decided to regulate ropers and, in 2006, required them to submit a "notification of use," a type of application also filed by crane operators. They also must be a licensed by the city as riggers.

"This is not mountain climbing—this is a specialized trade. We made a home for this work," said Tim Lynch, assistant city buildings commissioner and a trained roper.

The growth of roping hasn't had an impact on the number of scaffolds erected in the city, said Mr. Lynch, noting the two don't necessarily compete for elevated work since scaffolds are needed for repairs and construction, and ropers are useful for inspections or data gathering.

As for the future of ropers, industry leaders say they may get competition from new technology. Mr. Sampat predicts, "The new trend will be drones."