Nine white apartment buildings stand out like spaceships among the ageing brick facades of the Bushwick neighbourhood of Brooklyn, New York. The century-old buildings were recently upgraded with an energy-efficient exoskeleton, an effort to slash the buildings鈥� energy consumption in half while minimising disruption to tenants. This could serve as a model for the millions of building retrofits needed to meet climate targets.
at RiseBoro, the affordable housing organisation that developed the project, says the 鈥渟paghetti鈥� of piping and wiring for the building鈥檚 new electric heat pumps and heat-recycling ventilation system was attached to the outside of the buildings, then covered by the insulation. Efficient windows were added last.
This external retrofit, along with internal appliance upgrades, has cut building energy consumption by 60 per cent since construction finished at the end of 2022, says Cassidy. Models show the retrofit could lower building energy use as much as 80 per cent, but much depends on tenant behaviour.
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Standing in cold rain outside one of the buildings, Cassidy pointed to an open window on the second floor. 鈥淭he model assumes you wouldn鈥檛 have a window open in February,鈥� he said, frowning.
Tenants were central to the project鈥檚 conception. While tearing up the walls to do a more traditional upgrade would have forced tenants to move out for months, retrofitting from the exterior minimised disruption.
Angel Bonilla, a superintendent for several of the buildings, says tenants had to stay in hotels for two weeks during construction, and there were some complaints about noise and the scaffolding blocking light. But he says people were pleased overall. 鈥淚 haven鈥檛 really needed to use my heat,鈥� says Bonilla. Before, he had to run it constantly to stay warm.
The project, called Casa Pasiva, is the first to be supported under a聽New York . In New York City, up to will need retrofits by 2030 to comply with the city鈥檚 new emissions law passed in 2019.
The 鈥渢enant-in-place鈥� approach could also serve as a model for millions of other building retrofits needed to reduce energy demand enough to meet climate targets. In the US more than half of the buildings that will be standing in 2050 have already been built, many of them before building efficiency codes were in place. A US Department of Energy study found that , could reduce emissions from buildings by more than 90 per cent by 2050.
However, the study found that achieving those deep reductions would require an aggressive pace of construction. For instance, 4 million homes would need whole-building retrofits similar to the Casa Pasiva project each year between now and 2050.
The Inflation Reduction Act, passed in 2022, includes billions of dollars in subsidies to improve buildings鈥� energy efficiency and reduce their emissions. But, future projects will need to be cheaper and quicker to implement if they are going to happen at the scale needed to reach climate targets.
The bespoke design of Casa Pasiva meant it was relatively expensive, says at the New York State Energy Research and Development Authority. Cassidy says the retrofit cost around $120,000 per unit, half of which was covered by public funds.
A promising cost-cutting approach is to use lasers to scan existing buildings, then manufacture insulation panels that exactly match the exterior. Panels can then quickly be bolted on to buildings, cutting months of construction time down to days. The Casa Pasiva project took around three years to complete, in large part because of delays related to the covid-19 pandemic.
A Dutch initiative called has had success with this 鈥減anelisation鈥� approach. The group has prefabricated panels to retrofit more than 5000 houses in the Netherlands. There are more than a hundred test projects using this approach in progress in New York, and hundreds more planned in the UK, according to an Energiesprong representative.
, the architect who designed Casa Pasiva, says this approach may be better suited for more modular European houses. 鈥淲hen you take a close look at buildings in New York there鈥檚 a huge amount of variation,鈥� she says, and historic buildings in particular won鈥檛 fit the mould.
Benedict says the coming retrofits are likely to change many of the city鈥檚 classic, if fading, facades. But efficient buildings are more comfortable to live in and make neighbourhoods better, she says. 鈥淚 want people to change their eyes. We鈥檙e a part of history just like that facade was.鈥�
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