New York City’s passive house movement carries existing homes into a low energy revolution

In 2018, RiseBoro Community Partnership, a nonprofit afford­able housing devel­oper and social service commu­nity orga­ni­za­tion, had a choice about how to approach the reno­va­tion of 143 units across nine multi-family build­ings it owned in Bushwick, due for refi­nancing and upgrades. The orga­ni­za­tion decided that updating the 90-year-old devel­op­ment to reduce energy consump­tion was a no-brainer; RiseBoro was already a fron­trunner in terms of greening build­ings in New York after building the state’s first 100% afford­able passive house, nearby in Bushwick. 

Even though retro­fitting existing build­ings can pose a very different chal­lenge than imag­ining a new struc­ture from the ground up, RiseBoro decided to take a similar approach for the reno­va­tion — installing a hyper-insu­lated building exte­rior; tearing out old heating systems and replacing them with split unit heat pumps; and adding energy recovery venti­la­tors (ERVs) to the exte­rior— all in the service of mini­mizing the amount of energy needed for heating and cooling. These strate­gies come from the passive house move­ment, which was formal­ized as a volun­tary building certi­fi­ca­tion program in the 1970s during a global energy crisis. 

“We’re going to have these build­ings in perpe­tuity,” said Josh Shaffer, capital plan­ning and sustain­ability manager at RiseBoro. ​“So it really makes sense to build to a passive house stan­dard, because your oper­ating costs get lowered so substan­tially, and it just makes it easier to operate the building and provide a safe and comfort­able space for our tenants.”

They even­tu­ally dubbed the nine build­ings ​“Casa Pasiva,” which is ​“passive house” in Spanish, a nod to the building’s mostly Spanish-speaking resi­dents. Not only did the retrofit result in a 40 to 50 percent building-wide reduc­tion in energy use, but RiseBoro managed to execute the improve­ments without displacing tenants. 

As New York City’s building sector has been driven by policy in recent years to steer away from leaky build­ings and oil furnaces toward a cleaner and less carbon-inten­sive future, owners, devel­opers, and contrac­tors have been exper­i­menting with a myriad of inno­va­tions to make build­ings operate more efficiently. 

In the passive house stan­dard, builders are finding a proven approach to making build­ings more energy effi­cient that can support these efforts. The basic philos­ophy of the design frame­work is this: When build­ings are constructed to self-regu­late temper­a­ture — staying warm in the winter and cool in the summer — they require less energy to arti­fi­cially manip­u­late indoor temperature. 

“The inter­esting thing about passive house, which changes the game completely in New York, is if you do it well enough, you almost don’t need heat,” said Michael Ingui, pres­i­dent of New York firm Ingui Architecture and the founder of Passive House Accelerator, a plat­form for spreading knowl­edge and infor­ma­tion about passive house projects. 

Since passive house’s early days in Europe in the 70s, it has fully taken root in New York City. The city now boasts a number of inno­v­a­tive passive house projects, including The House at CornellTech, a 26-story resi­den­tial tower that was at one time the largest passive house building in the world; Engine 16, a former fire­house turned church turned multi­family passive house; and now, Sendero Verde, the East Harlem devel­op­ment that offers more than 700 units of afford­able housing built to passive house standards.

Typically, passive house stan­dards have been applied to new construc­tion and single family homes. But New York City is proving that these concepts can be also applied to existing build­ings through retro­fits — even on historic build­ings, or co-ops and condos that have exte­rior aesthetic require­ments. What’s more, these changes don’t have to be prohib­i­tively expen­sive; most build­ings can justify passive house appli­ca­tions based on a simple ROI calcu­la­tion, even without subsidies. 

“High-perfor­mance, low-carbon build­ings are not just possible, but scal­able and essen­tial to the future of our commu­ni­ties,” said Shaffer. 

Passive house 101: What makes a passive house?

Passive house is premised on five central concepts: A well-insu­lated enve­lope, an airtight enve­lope, reducing thermal bridges, high perfor­mance windows and doors, and balanced heat recovery. These prin­ci­ples can be applied to new construc­tion and to existing build­ings alike. Here is a breakdown:

1. Insulated building enve­lope: A building should have a contin­uous layer of insu­la­tion to retain consis­tent temper­a­ture, which helps keep the building warm in the winter and cool in the summer. 
2. Airtight enve­lope: In addi­tion to insu­la­tion, the whole building enve­lope — that is, the exte­rior walls, roof, and base­ment — should include another layer that acts like a wind­breaker and stops air from pene­trating to the inside. Air barriers can be built with sheet membranes, fluid-applied membranes, tapes, and sealants that tran­si­tion between compo­nents of the building envelope.
3. High-perfor­mance windows and doors: Windows and doors are points of entry for cold and hot air. Having high-perfor­mance doors and triple-pane windows reduces that leakage.
4. Balanced heat recovery: Filtered fresh air helps make passive house build­ings healthy living spaces for resi­dents, which is espe­cially impor­tant because the build­ings are designed to be airtight. HRVs (heat recovery venti­la­tors) and ERVs (energy recovery venti­la­tors) are two types of ​“balanced venti­la­tion” compo­nents: In the winter, they allow heat energy in the outgoing air to passively transfer to and warm the incoming air, without the two airstreams ever mixing. In the summer, it’s the reverse.
5. Reducing thermal bridges: A thermal bridge is any building element that allows heat or cold to bypass a building’s thermal barrier — for example, a concrete floor that continues from inside to outside, or a beam that pene­trates an exte­rior wall. Thermal bridges can be mini­mized or elim­i­nated by intro­ducing gaps or insu­la­tion to inter­rupt the transfer of heat or cold.

The passive house movement in New York City

Interest in passive houses has been growing in New York City in recent years. Carmel Pratt, the exec­u­tive director of New York Passive House, which is the leading nonprofit orga­ni­za­tion that supports the move­ment in New York City and New York State, told Skylight that an encour­aging policy climate has led to an uptick in project certi­fi­ca­tions in New York City. 

There are currently two path­ways to certi­fi­ca­tion. One is the inter­na­tional stan­dard through the Passivhaus Institute (PHI). The other is the North American Standard through Passive House Institute U.S. (PHIUS). Collectively, the two orga­ni­za­tions have certi­fied millions of building square footage in the United States. 

“When [passive houses] first came out, it was seen as this premium, more expen­sive thing… and that’s kind of flipped in the oppo­site end in a really great way,” said Pratt. ​“We’re now seeing the scale tip that actu­ally many more really large scale multi­family afford­able housing projects are pursuing the certi­fi­ca­tion standard.”

Ingui concurs: ​“Because of the scale, whether it’s afford­able housing or it’s market-rate housing, [doing a passive house retrofit] winds up becoming cost neutral at a minimum for large devel­op­ment projects.”

One cata­lyst for the increase in projects has been incen­tives from state and local author­i­ties to reduce the cost of adopting passive house in New York. New York state’s Clean Energy Initiative, in part­ner­ship with housing agency Homes and Community Renewal (HCR), offers low interest loans for afford­able new construc­tion and reha­bil­i­ta­tion projects that pursue passive house stan­dards. This funding is designed to help projects meet sustain­ability guide­lines required by HCR. 

Incentives also exist at the city level; the city’s Housing and Preservation Department (HPD), in part­ner­ship with the New York State Energy and Research Development Authority (NYSERDA), provides addi­tional funding through the Future Housing Initiative to new construc­tion projects pursuing passive house certification.

“Now it’s our work to get market rate and luxury to see the bene­fits,” Pratt added. ​“There’s still a great ROI finan­cial incen­tive to pursue passive house for a long term oper­a­tional costs benefit, not just [for] a poten­tial subsidy.”

Retrofits in action

Bed-Stuy Passive House

When Ruth Mandl, co-founder and prin­cipal of design and build prac­tice CO Adaptive, bought a brown­stone with her partner in Bedford-Stuyvesant in Brooklyn in 2016, she knew from the start she wanted to do a passive house renovation. 

“If you’re going to do anything close to a gut reno­va­tion, reno­vating to passive house stan­dards is only a five to 10 percent increase on a stan­dard construc­tion” based on costs at the time, said Mandl. ​“And that pays off in the lack of energy bills over seven to 10 years.” Her building is now totally elec­tric, and since the energy consump­tion is so low, the load is entirely covered by a rooftop solar system, which also powers an elec­tric vehicle.

She pointed out that the passive house design is also about comfort for the people who live there. ​“You can sit by a window in the cold of winter in your under­wear and you’re not cold,” she said. ​“And the fact that that sort of package…is also good for our planet? I mean, it’s a no brainer.” 

The retrofit involved the appli­ca­tion of substan­tial blown-in cellu­lose along with mineral wool batts on the inte­rior of the building, in order to provide insu­la­tion while preserving the historic exte­rior. Additionally, roughly a dozen tilt-and-turn, triple-pane windows were installed, with oper­able exte­rior shades to miti­gate solar heat gain in the summer. In order to mini­mize pene­tra­tions in the house’s air-tight membrane, new plumbing, elec­trical, and venti­la­tion systems were located within an inte­rior central spine from which they branched out to service each floor. The project is now in the final stages of approval for certi­fi­ca­tion with PHI.

“Once you expe­ri­ence [a passive house], it’s sort of a no-brainer that this is the future of building,” said Mandl. ​“While construc­tion prices are climbing and energy prices are climbing, [with a passive house,] you’re at a stable point, right? And that, I think, is what’s special. So while it was defi­nitely more than anybody would have invested in our neigh­bor­hood at that time, we knew we were going to live in that house. And it wasn’t about resale value, it was about a home for us. I am beyond happy now.”

Mandl and her family did not live in the home during most of this reno­va­tion, but she recog­nizes that in order to update the city’s existing housing stock, many retro­fits will have to happen with people inside their homes. 

RiseBoro simi­larly mini­mized the amount of work needed to be done on the Casa Pasiva units by putting new cladding on the building exte­rior. In this way, they were able to keep tenants in place during the reno­va­tion. But for some homes, that is not a possibility. 

“There’s a lot of old housing stock in New York, including old tene­ment build­ings, where it’s really hard to get the building to an entirely empty state to do a passive house reno­va­tion,” said Mandl. 

Three Arts

Three Arts, a 62-unit high rise apart­ment building in Manhattan, was built in 1926 as the first resi­dence in the United States intended for young women in the arts. Almost 100 years later, it is under­going a massive reha­bil­i­ta­tion to continue to support a different special­ized popu­la­tion, this time providing deeply-afford­able housing for seniors. 

“We’re actu­ally providing homes for people who need it,” said Sean Flynn, of Curtis + Ginsberg Architects. ​“And we’re also making a building that conforms to the best possible stan­dards for energy use and the stan­dards neces­sary to cherish its history and be respectful of its importance.”

Curtis + Ginsberg Architects have a habit of recom­mending passive design to clients. Flynn said that the Three Arts owner, West Side Federation for Senior and Supportive Housing, was fully supportive of the vision. 

The combi­na­tion of Department of Interior stan­dards for historic places as well as New York Landmark District rules presented various obsta­cles to designing the building to passive house stan­dards. A newly insu­lated exte­rior was off the table, and the inte­rior walls could not be built in more than three inches. Though Curtis + Ginsberg Architects would have preferred to install more insu­la­tion, they installed only 2.5 inches (plus half an inch of gypsum board) from the inside. But even so, the modi­fi­ca­tions are expected to be effec­tive — the building is still on track for a passive house certi­fi­ca­tion from PHI. 

The retrofit also includes triple-pane windows, pack­aged terminal heat pumps for space condi­tioning, air-source heat pumps for domestic hot water, and central­ized energy recovery venti­la­tion. The reno­va­tion is expected to be completed by the end of 2027, and the project has already received a $1 million award from NYSERDA through its Buildings of Excellence program. 

Flynn noted that in addi­tion to reducing oper­ating costs, passive house design brings non-mone­tary bene­fits to its residents. 

“Particularly for senior housing, draft-free, evenly heated spaces are extremely bene­fi­cial. The filtered air that’s brought in through energy recovery venti­la­tion systems is also extremely beneficial.”

RiseBoro looks to the future

While RiseBoro puts the finishing touches on the Casa Pasiva reha­bil­i­ta­tion, they look to the future for more oppor­tu­ni­ties to build and reha­bil­i­tate to passive house stan­dards. They recently began reha­bil­i­tating a 24-building scat­tered site with 3 – 6 unit build­ings also in Bushwick, where they will continue to pursue passive house retro­fits when feasible. 

“These projects repre­sent a shift in how afford­able housing can lead on climate, health, and long-term resilience,” Shaffer said. ​“We do what we can within the given budgets and on-site circum­stances, but our target is always to build to a passive house standard.”

Reporting contributed by Camille Squires.