How 9/11 Changed Standards of Building and Safety

The International Building Code Gets Revised

computer presentation slide of wing tips in contact with building, horizontal angle -4.3 degrees, vertical angle -6.2 degrees, and roll -20.7 degrees
An April 2003 Presentation by Structural Engineers Explaining Why the Twin Towers Collapsed on 9/11. Stephen Chernin/Getty Images (cropped)

Before September 11, 2001, building codes in the United States focused on structural stability and routine fire safety. Buildings like the twin towers at the World Trade Center were considered safe because they could withstand hurricane-force winds and even the impact of a small plane. They were over-built to not fall down. A typical fire did not spread beyond a few floors, so skyscrapers weren't required to provide multiple escape routes for speedy evacuation of the entire building. Using fewer stairways and slim, lightweight construction materials, architects could design skyscrapers that were slender, elegant, and amazingly tall.

About Building Codes

Rules and regulations that outline good and safe construction, fire safety, plumbing, electrical, and energy are generally "codified," which means they become law. These codes are administered and enforced regionally and locally. Across the United States, states and localities "adopt" model codes — a set of best practices building standards that have been created by a council of independent experts. Most states adopt and modify standard codes, such as the International Building Code® (IBC) and the International Fire Code.®

On January 1, 2003, New York State adopted the International Building Codes, "...which are widely used throughout the country, provide a greater level of consistency and allow us to keep pace with emerging technology in today’s fast paced construction industry," writes the NYS Division of Code Enforcement. Up until then, New York State was one of the few states who wrote and maintained their own codes, independent of standard model codes.

Construction codes (e.g., building, fire, electrical codes) are legislated by individual states and localities in the United States. Local building codes, such as the New York City Code, can be more stringent (i.e., more strict) than state codes, but local codes cannot be less stringent than state codes.

Building codes in New York City have existed since the city was called New Amsterdam in the 17th century. When the first skyscrapers were being built at the turn of the 20th century, it was the building code that enforced architects to design buildings that would allow sunshine onto the street, which is why many of the old skyscrapers are "stepped," with tiers and cut-outs at the top. Building Codes are dynamic documents — they change when circumstances change.

After September 11, 2001

After two aircraft struck and brought down the twin towers in New York City, teams of architects and engineers studied why the World Trade Center towers fell. The reports issued by the Federal Emergency Management Agency (FEMA), the National 9/11 Commission, and the National Institute of Standards and Technology (NIST) included recommendations of ways to make future skyscrapers safer. From 2005 to 2008 NIST compiled their findings in a series of reports, including a study of the collapse of building seven at ground zero.

The office building known as WTC 7 was a more typical New York City skyscraper compared with the super-tall twin towers that had been hit by jets and jet fuel. Building seven stood for nearly seven more hours after the nearby north tower collapsed. Crumbling at 5:20:52 p.m. ET after a long day of terror, WTC 7 was never attacked, but it, too, collapsed. In its report, NIST claims that this building's collapse "was the first known instance of the total collapse of a tall building primarily due to fires." Other buildings in New York City have had fires, even as their sprinkler systems have not function, yet WTC 7 is the only one to have collapsed. In fact, in 1945 and Air Force bomber accidentally flew into the Empire State Building one foggy morning, and the skyscraper built in 1931 did not collapse.

NIST observed that "the collapse of WTC 7 highlights the importance of designing fire-resistant structures for situations where sprinklers are not present, do not function (e.g., due to disconnected or impaired water supply), or are overwhelmed." The WTC 7 fell on 9/11 because of "a fire-induced progressive collapse...the spread of local damage, from an initiating event...." The building met the New York City building codes of 1968 — regulations written over thirty years before 9/11.

The age of a building code should not matter, however. On the south end of the World Trade Center site, a 23-story Gothic skyscraper designed by Cass Gilbert never collapsed although it was heavily damaged on 9/11. The steel frame of the 1907 building built at 90 West Street was reinforced with heat-resistant terra cotta, tile, and concrete.

New York City, which suffered the most catastrophic losses on 9/11/01, took the lead passing legislation to save lives in the event of another terrorist attack. In 2004, New York City Mayor Michael Bloomburg signed Local Law 26, which required tall buildings to incorporate improved sprinkler systems, better exit signs, an additional stairway, and other features to help people exit quickly during emergencies.

Nationally, change came more slowly. Some people worried that more demanding building code laws would make it difficult, if not impossible, to construct record-breaking skyscrapers. They wondered whether architects would be able to design beautiful, slender skyscrapers with enough stairways or elevators to meet the new safety regulations.

Critics also charged that new, more rigid safety requirements would increase construction costs. At one point the General Services Administration (GSA), a federal agency that manages government property, estimated that the expense of installing additional stairways would outweigh the safety benefits.

man in suit gesturing near a poster of Analysis of Probable Collapse Sequence
April 2005 Presentation by Lead Investigator Shyam Sunder, NIST. Stephen Chernin/Getty Images (cropped)

Building Code Changes

NIST was not prescriptive in its recommendations. Instead, NIST encouraged competitive solutions to the issues it raised and supported public policymakers to adopt revised standards and codes By 2009, the push for new construction standards won out, bringing sweeping changes to the International Building Code and the International Fire Code, which serve as the basis for building and fire regulations across the United States. The International Code Council (ICC) approve changes every three years when the codes are updated.

Some of the new safety requirements for buildings included additional stairways and more space between stairways; stronger walls in stairwells and elevator shafts; reinforced elevators for emergency use; stricter standards for construction materials; better fire-proofing; backup water sources for the sprinkler system; glow-in-the-dark exit signs; and radio amplifiers for emergency communications.

The End of Elegance?

In 1974, the City of Los Angeles passed an ordinance requiring helipads atop all commercial high-rises. Firefighters thought it was a good idea. Developers and architects felt the flat-top requirements stifled a creative skyline. In 2014 the local regulation was rescinded.

Architects face difficult challenges as they grapple with more demanding fire and safety codes. In New York City, disputes over the design of Freedom Tower became legendary. As safety concerns mounted, the original concept posed by architect Daniel Libeskind morphed into a less fanciful skyscraper designed and then re-designed by architect David Childs.

The final design for One World Trade Center resolved many complaints. New concrete materials and construction techniques have made it possible to incorporate fire-safety features with open floor plans and transparent glass walls. Still, some fans of the original Freedom Tower design say that Childs sacrificed art for the sake of an impossible-to-achieve notion of security. Others say the new 1 WTC is everything it should be.

The New Normal: Architecture, Safety, and Sustainability

So, what is the future for skyscrapers? Do the new safety laws mean shorter, fatter buildings? Absolutely not. Completed in 2010, the Burj Khalifa in the United Arab Emirates shattered world records for building height. Yet, while it rises a whopping 2,717 feet (828 meters), the skyscraper incorporates multiple evacuation lifts, super-high-speed elevators, thick concrete reinforcement in the stairways, and many other safety features.

Of course, a building as tall as Burj Khalifa poses other problems. The maintenance costs are astronomical and the demands on natural resources extreme.These shortfalls point out the real challenge that every designer faces.

One World Trade Center stands near where the destroyed twin towers once stood, replacing office space but never taking the place of memories — the National 9/11 Memorial is now where the twin towers stood. A number of safety, security, and green building features have been incorporated into the design and construction of the new 1WTC, design details that may have been missing in the original buildings. For example, safety systems now exceed the requirements of the New York City Building Code; elevators are housed in a protected central building core; protected tenant collection points are on each floor; a dedicated staircase for firefighters and extra-wide pressurized staircases are part of the design; sprinklers, emergency risers, and communication systems are concrete-protected; the building is the most environmentally sustainable project of its size in the world, attaining a LEED Gold Certification; the building's energy performance exceeds code requirements by 20 percent, cooling systems use reclaimed rainwater, and waste steam helps generate electricity.

The Bottom Line

Designing buildings has always meant working within rules. In addition to fire codes and safety laws, modern-day construction must meet established standards for environmental protection, energy efficiency, and universal accessibility. Local zoning ordinances impose additional restrictions that can affect anything from paint colors to architectural style. And then, of course, successful buildings also respond to the demands of the landscape and the needs of the client and the community.

As new rules are added to the already complex web of regulations and restrictions, architects and engineers are doing what they have always done so well — innovate. Ask about the building / fire codes / standards in other countries, and watch the horizon for the tallest buildings in the world.

We are in a new world, redefining what is feasible.

Summary: 8 Areas of Needed Change — NIST Recommendations

  1. Increase structural integrity to prevent progressive collapse
  2. Enhance fire endurance, including ratings and testing of spray-applied materials
  3. Create new methods for fire resistant design, including burnout without collapse
  4. Improve active fire protection systems ("design, performance, reliability, and redundancy") such as sprinklers, alarms, etc.
  5. Improve building evacuation and emergency communication procedures and design
  6. Improve emergency response, including command and control
  7. Improve procedures and practices, including code compliance and documentation
  8. Education and training ("for fire protection engineers, structural engineers, architects, and building regulatory and fire service personnel")


  • National Institute of Standards and Technology (NIST). Final Reports from the NIST World Trade Center Disaster Investigation. September 2005 to November 2008.
  • Barbara A. Nadel, FAIA. "High-Rise Intl. Building Code Changes Reflect Lessons Learned from 9/11.", November 6, 2008.
  • The Port Authority of New York & New Jersey. One World Trade Center Progress.
  • New York State Department of State. About the Division of Building Standards and Codes.
  • Patrick Butler. "Maybe L.A.'s 'stupid' helipad rule wasn't so dumb." Los Angeles Times Op-Ed, October 6, 2014.