When Hurricane Sandy made landfall in NYC in 2012, the resulting damage cost the city around $19 billion. The storm left around 20% of New Yorkers without power, completely flooded the subway system and even shut down the stock exchange for two days. In addition, around 20,000 buildings were damaged and there were more than 50 casualties.

Due to the severe damage caused by the storm, the NYC government decided that buildings had to become more resistant to extreme weather. A Building Resiliency Task Force was created to identify promising measures, with more than 200 volunteers with relevant experience led by the Urban Green Council. Their recommendations included building code revisions, as well as the removal of legal barriers that were detrimental for building resilience.

In general, building equipment is more vulnerable if it relies on a constant power supply or a complex underlying system. The same technologies that make buildings smarter and more habitable under normal conditions can become obstacles during an emergency.

Improving Buildings to Provide Shelter During Emergencies

Many of the recommendations provided by the Building Resiliency Task Force focused on improving the buildings themselves. In general, there are two main types of recommendations: those that improve the buildings’ ability to withstand damage, and those that make them safer for occupants during emergency conditions. Due to the high population density, evacuating large portions of NYC is unfeasible, so buildings must be effective shelters.

One of the key risk factors detected was the use of rooftop gravel, which can be blown away by the wind. Each pebble becomes a dangerous projectile that can damage windows, vehicles or even people. The BRTF recommends the use of rooftop pavers instead, which are more resistant to the wind. In the case of residential buildings, outdoor furniture and plants are also common, and should be anchored in place or brought inside to prevent them from becoming airborne under strong winds.

In many areas of NYC, the water supply can reach up to the fifth floor without pumping equipment. However a key issue was detected in high-rise buildings: important systems are located in the basement or lower floors, and can be taken out of operation by floodwater. During Hurricane Sandy, for example, many buildings that depended on electric water pumps were left without potable water because the pumps were flooded. To address this issue, the BRTF proposed an amendment to the building code, where common area faucets independent from the main pumping system must be provided to guarantee a water supply under emergency conditions.

The BRTF also suggested using fully openable windows on multifamily buildings. Many properties use windows that only open a few inches, under the assumption that mechanical ventilation will always be available. These properties were not adequately ventilated during Hurricane Sandy, since they relied completely on the limited window area. In addition, wind-resistant doors and windows can be specified for new constructions and renovations to existing buildings.

Lack of insulation is another common issue, and many NYC buildings cannot sustain adequate temperatures for long if their HVAC systems are left without power. However, during adverse weather conditions their occupants may have nowhere to go. Poor insulation is an issue during both heat waves and extreme cold.

Sewage backflow also affected many properties during the flood caused by Hurricane Sandy, so the BRTF suggested the use of check valves in areas prone to flooding. Automatic toilets were also an issue, since they rely on electricity for flushing; they must be equipped with long-life batteries or a manual override to allow flushing during emergencies.

Stored hazardous materials are also a risk factor during a flood, and it is important to ensure they will not be mixed with floodwaters. The combination of stagnant water, sewage backflow and hazardous materials is a severe health risk for humans.

Flood Mitigation

Two complementary approaches were suggested by the BRTF to control flooding. One was to equip buildings with rainwater retention systems, reducing the flowrate into the NYC sewage system. In addition, collected rainwater can be used for purposes such a toilet flushing in buildings where the water supply has been interrupted.

With respect to the water that has already reached the streets, there are many simple measures that can mitigate its impact on buildings:

• Sloped sidewalks.
• Tree pits with wind- and salt-tolerant tree species, given that storm surges bring seawater.
• Temporary flood barriers and sandbags.

Another effective mitigation strategy is to simply install important equipment in higher floors. Even if the electric supply is interrupted, equipment can continue to operate with backup power.

Low-rise buildings can be constructed on elevated bases to make them less vulnerable to flooding. The main limitation here was legal according to the BRTF, since that type of construction is not allowed in many NYC neighborhoods. Around 71,000 properties are located in zones with a 1% chance of flooding per year - although the probability seems low, the economic and human consequences are too severe to be overlooked.

Gas-Fired Equipment

The natural gas distribution system of NYC withstood Hurricane Sandy without major service interruptions. The BRTF emphasized the potential of gas during emergency situations, since it can be used not only for heating, but also to operate compatible electrical generators.

Compared with diesel, natural gas produces less emissions and offers a higher efficiency. It can also be used to power a cogeneration system, where the waste heat from electricity generation is used for space and water heating. If the building is equipped with a photovoltaic array, solar power can complement the gas generator. Solar PV systems are unlikely to stop operating during harsh weather, since they are located high above the range of floodwaters and are firmly anchored to the rooftop. The most serious issue they are likely to face is reduced energy generation because of the clouds.

An emergency power supply is important for many building systems, but critical for Fire Department communication equipment, which plays a key role during emergencies. Rescue operations are very difficult to coordinate when buildings are left without communication. Means of egress such as staircases and hallways must also be provided with a reliable backup power supply for their lighting systems.

Favorable Legislation for Volunteer Work

After Hurricane Sandy, many engineering and architecture professionals were afraid to perform volunteer work. Despite their good intentions, they had no protection against liabilities, so the BRTF proposed “good samaritan” legislation to ensure that professionals offering voluntary services were waived from any legal action against them.

Professional services are a key element in making NYC infrastructure more resistant to extreme weather. Many of the BRTF recommendations have already been incorporated into NYC building codes, and professional engineering services make compliance simpler while ensuring safe construction.