New York City’s immense, dense building stock constitutes such a significant risk exposure that this section begins by focusing upon risk-mitigation actions to strengthen buildings.

NYC Construction Codes

Since 2008, New York City Construction Codes have included provisions requiring that new buildings be able to withstand high winds in a dense, high-rise environment.

The Building Code, a component of New York City Construction Codes, contains wind-exposure categories that establish design requirements for location, surroundings, and occupancy, so that all new buildings can withstand high winds. For example, building along the coastline and buildings taller than 300 feet are subject to higher wind load requirements.

The Building Code also requires that New York City buildings be designed to resist high wind events. Severe thunderstorms, Nor’easters, and other non-thunderstorm high wind events occur in New York City more frequently than hurricanes.  Due to concern about withstanding hurricane-force winds, buildings here are designed to sustain effects of wind that develop  higher pressures than most of the strong wind events experienced in NYC. The Building Code also contains wind-resistance criteria for certain building components and façade systems.

New York City’s Construction Codes specify design standards that minimize risk from hurricane-level winds that are most likely to occur in the eastern part of the United States. The standards also contain provisions to mitigate risks from the unique wind hazards associated with New York City’s dense, high-rise environment. New buildings and older buildings that are undergoing major renovations are required to meet these standards.

New Buildings

New buildings are designed and constructed so that they are able to resist high-wind events- this includes the building structure and envelope.

Structural engineers use highly refined methods to analyze how buildings and structures respond to wind loads. Most of the wind loads on high rises in New York City are evaluated using wind tunnel testing.  Wind tunnel testing uses small-scale models of the built environment and simulates various levels of wind conditions. The structures are designed with highly sophisticated computer programs that provide for the building’s resistance to wind, but also account for the comfort of occupants during high wind events.

Retrofitting Existing Buildings

Older buildings can be retrofitted to withstand high wind loads. Recommended measures include:

• Strengthening the connections of a building's structural components by anchoring a wooden building to its foundations and by anchoring its roof frame to load-bearing walls.
• Replacing unreinforced brick masonry parapets with reinforced masonry parapets that are securely anchored to the rest of the building.
• Replacing roof covering with larger pavers to meet code standards, in order to reduce the risk of their pavers being blown off.
• Installing windows that are rated by the American Architectural Manufacturers Association (AAMA).
• Installing window shutters.
• Reinforcing and securing rooftop equipment, such as heating, ventilation, and air conditioning units.

Protecting our existing building stock requires inspection, maintenance, and repair of structural weaknesses.

Maintaining Older Buildings

For buildings whose construction predates the 1968 Building Code, maintenance is particularly important to lower the risk of damage from high winds. Measures include:

• Keeping roofs tight and in good condition.
• Inspecting the wood regularly to identify rot.
• Securing cornices.
• Repointing mortar regularly and fixing cracks, especially on chimneys and parapets.
• Replacing any glass that is not rated for New York City winds. For buildings under 100 feet high, the standard is 30 pounds per square foot.
• Making sure that all windows and doors (and any other opening) can be shut completely whenever high winds are predicted.

The New York City Department of Buildings (DOB) Façade Safety Inspection Program reduces risk from high winds by identifying the need to make repairs and to protect buildings on a regular basis. The program requires owners of buildings taller than six stories to have exterior walls and appurtenances inspected once every five years and to file a technical report with the DOB.

Mitigating Hail Damage

Retrofitting and design strategies can also be used to minimize damage caused by hail. These measures include:

• Installing structural bracing, shutters, and laminated glass in window panes, and including hail-resistant roof coverings or flashing in the building design to minimize damage.
• Obtaining information from the Insurance Institute for Business and Home Safety (IBHS) about the most appropriate type of roof covering for the New York City region.
• Improving roof sheathing to prevent hail penetration.

Research Initiatives

Ongoing research on the following topics informs future revisions to the New York City Construction Codes:

• How high winds impact different building types, partially completed buildings, and construction sites.
• How a building’s age, construction, materials, and height affect its vulnerability to structural damage from high winds.

The Mayor's Office of Recovery and Resiliency, in consultation with DOB, is required by Local Law 81 of 2013 to complete a report to analyze the impact of high winds on certain at-risk buildings. The study will:

• Identify the types of existing buildings that are at risk of causing falling debris due to wind, based on their age, construction classification, construction methods and materials, height, and occupancy use.
• Analyze the effects of wind on buildings that are raised/elevated and buildings that are under construction.
• Forecast potential changes in the frequency, intensity, and path of future storm events and consider whether climate change and other factors might impact wind speeds affecting New York City in the future.
• Examine the benefits of installing and maintaining weather stations across New York City, including stations in high-rise buildings, to better understand the city’s localized wind patterns.

New York City’s trees are exceptionally vulnerable during high winds. High winds could cause large tree limbs to fall or entire trees to topple. Pruning trees and taking appropriate tree maintenance strategies can help reduce this risk.  The Department of Parks Central Forestry Division oversees block pruning and commitment-pruning programs, in which they prune street trees on a neighborhood by neighborhood basis allowing for the department to prune a portion of street trees in each community board every year. Commitment pruning deals with emergency situations such as tree limbs obscuring traffic signals. The Division also prunes trees in parks.

A similar program is Con Edison's vegetation maintenance program, which trims branches near power lines along right of ways.  This initiative also removes damaged or unhealthy trees and vegetation to create safe, minimum cleared distances between power lines and the surrounding trees. Every three years, Con Edison returns to trim back growth and to reestablish the minimum clearance.

Public Warnings and Alerts

When dangerous weather conditions threaten, New York City monitors and disseminates the information it receives from the National Weather Service and other sources. The National Weather Service (NWS) Storm Prediction Center (SPC) issues a Severe Thunderstorm Watch whenever a large, multistate area is at risk, providing a few hours’ notice in which to take necessary precautions against wind and rain hazards. The NWS SPC issues a Severe Thunderstorm Warning either during the storm or very soon before it is expected to occur. The timing of this warning can range from a few minutes to an hour ahead of the danger.

Because damaging winds can arrive suddenly, New Yorkers need to be prepared ahead of time to respond to alerts such as a Severe Thunderstorm Warning. New York City’s communication strategies include:

• Using multiple channels, including text messaging, email, local radio, TV stations, and social media, to issue emergency alerts regarding forecasted severe thunderstorms or other high-wind events.
• Targeting populations with disability, access, and functional needs.
• Communicating in multiple languages to reach many segments of New York City’s diverse population.

Notify NYC is the City's official source of information about emergency situations, and is used prior to and during high-wind events. NYC Emergency Management sends Notify NYC notifications and alerts swiftly to over more than 250,000 subscribers.

Construction Site and Property Alerts

Another important communication strategy to reduce the risk of high-wind hazards is sending weather advisory notifications to property owners, contractors, and developers. These notifications alert this community to specific preventive actions that they can take quickly, such as removing loose construction materials from sites and securing loose items that could become airborne in high winds.

DOB offers building owners the option of subscribing to receive weather advisories. DOB issues Inclement Weather Advisories to property owners, builders, and contractors, which include advice on precautions to take to prepare for high winds at their properties. The DOB Preparing Sites for Extreme Weather Guide provides more detailed instructions on how to secure buildings and sites prior to a high-wind event. To enforce safety, violation notices are issued when construction sites are not safely secured.

Public Education

Longer-term education efforts help New Yorkers to prepare for and respond to hazards from high winds. Helpful messages include:

Take cover! New Yorkers generally have less than an hour of time to heed warnings that tornadoes and damaging winds from severe thunderstorms are about to strike. Sometimes warnings come as the hazard is imminent, giving only a few minutes of warning or none at all. Warnings for nor’easters, tropical cyclones, and other types of high-wind events often are issued 12 hours to a few days in advance. The best strategy for building occupants is to take cover in the most secure area of their building.

• People should know the safest places to take cover inside a building ahead of a tornado or other high-wind emergency.
• Furniture on porches, balconies, other outdoors places, and other loose items should immediately be secured.
• Building owners and residents should have emergency action plans that define procedures to be followed if a building-related incident or emergency happens.

NYCEM’s Ready New York: My Emergency Plan  provides information on how households can prepare to stay safe during severe weather events like severe winds.

The NYC Emergency Management  Reduce Your Risk guide explains to New Yorkers, and in particular to homeowners, how to reduce risks posed by tornadoes and other strong windstorms. Advice includes performing routine building maintenance, inspecting buildings for structural weaknesses, and making needed repairs.

Link: High Winds - Bibliography