Inside the Project: The Largest Phius Building to Date

425 Grand Concourse is located in one of the poorest congressional districts, which also happens to be most impacted by pervasive asthma in the population due to its high air pollution from heavy traffic and solid waste transfer stations. What better development to be had there than a passive house which addresses both impacts? Tenants will pay less for their cooling in the summer as a passive house is very well insulated and uses highly efficient heating and cooling equipment (heating is being paid for by the developer as a function of affordable housing). A passive house also minimizes the release of harmful, asthma-triggering combustion gasses both for tenants and the surrounding neighborhood by using electricity for heating and cooling as well as for cooking, and uses filtered fresh supply air for ventilation. The current building code still allows fresh air to be provided through so-called trickle vents – holes in the window frame, but if you live in an area with high air pollution unfiltered outside air is not really healthy.

Right after the award of the project by the City, and before we really put pen to paper, we sat down with our architect John Woelfling and his team from Dattner Architects as well as our sustainability and passive house consultants Lois Arena and Dylan Martello from Steven Winter Associates (SWA) to figure out which verification system made most sense for this project. SWA put a matrix together comparing thresholds and requirements for both Passive House Institute (PHI) and Phius.

There are a number of minor differences between the two certification requirements, but two really stood out for us. 

First, PHI didn’t consider the local climate when modeling the project. It is important to know that the PHI standard was developed in western Germany that has a markedly different climate than New York City. We were very concerned that if we didn’t take New York City’s climate – which is much more humid, but also warmer – into account, we could run into overheating and humidity issues if we follow the PHI pathway. Secondly, PHI didn’t let us control the expected occupancy density and other factors determining interior relative humidity levels in the energy model, and we were very concerned about humidity build-up and surface condensation.

We ended up interviewing both PHI and Phius and asked each organization how our concerns would be addressed. Though both organizations made some suggestions, Phius was more willing to work with our high-density passive house project and figure out workable solutions on this building typology – a building typology that even now is largely unrepresented in completed examples.

We had to make it work without specific funding for passive house. The New York State Energy Research and Development Authority (NYSERDA) provides some as-of-right funding for energy-efficient construction which we accessed. In addition, this project had the good fortune to be a winner of NYSERDA’s Round 1 Buildings of Excellence Competition, which comes with additional award money. Though we couldn’t use that for financing as it came in after construction financing closing.

Another financial tool on this project was the modeling of reduced utility costs during building operation. The funding agency allowed us to underwrite reduced utility costs, which in turn helped reduce permanent financing costs and made the often-heard “passive house premium” more financeable.

Phius projects on average are only 2% more than code buildings, but the value behind a better building is more than 2%.

This is the magic question everyone is asking, typically formulated as “What is the passive house premium?” I would counter by asking: “What is the ‘premium’ between a passive house and a high-quality, tested and commissioned building?” The answer would be close to none. 

Focus in real estate is usually placed on life safety (hopefully at least), exterior appearance and interior finishes. Nobody cares about how the “guts” of a building are really put together. I have seen buildings where insulation more or less gets thrown into the cavity behind a brick façade. Or where the so-called “building paper” (weather barrier) gets stapled to the underlying wood sheathing without sealing all the staple penetrations – in both cases completely defying the purpose of these materials. And since these assemblies are not easily accessible for inspection, they mostly don’t get inspected, or if inspected, get noted, but not properly corrected.

With passive house, I’m buying a high degree of quality assurance and building science that I otherwise would not have to, simply because I have to prove air tightness through testing. In the case of 425 Grand Concourse, we haven’t tested the entire building for air tightness yet¹, but I’m bullish that we will pass as we worked very hard on both design and construction and verified with inspection. We did some preliminary limited air tightness testing, and the results look very promising.

¹ The project has since undergone such testing and the building envelope and all interior spaces – residential and non-residential – delivered performance at half the maximum ceiling levels allowable to achieve Phius certification.

I did not foresee that we would make this building an R&D lab. Initially, passive house just seemed to make good sense for this project by lowering the energy consumption and utility costs, but diving deeper into the building science and financing made it clear that a number of aspects of passive house were not fully understood for this type of building: high-density high-rise buildings in a humid subtropical climate (e.g. New York City) behave differently from medium-density or low-density buildings in temperate oceanic climates (i.e. western Europe).

Insulation, glazing, glazing exposure in a dense city environment and wall-to-window ratio, along with humidity management become very important. We think, confirmed by all the modeling we did, that we struck the right balance in this building. The big unknown factor in our case is the specific occupancy – how many people will occupy, for example, a specific two-bedroom unit, how often will they cook at home, house plants, pets, showers, use of electronics (think working/learning from home in addition to home entertainment) – all of this factors into the question of when will our building need to cool vs. heat. We believe our building will be cooling-dominated, based on the expected interior heat gains. If this is the case, we have some way of managing the interior relative humidity with energy recovery ventilation as it will retain the relatively lower total humidity from the inside air during the hot and humid season, supplemented by the inherent dehumidification through the evaporator units in cooling mode. 

For shoulder months, but also for very cold winter nights, our MEP engineer Dagher Engineering had to develop a by-pass “flush” option whenever our exhaust air relative humidity level rises above a certain threshold: The exhaust air will bypass the ERV enthalpy wheel and not transfer heat and humidity to the incoming fresh air stream. This will help us lower the interior relative humidity so we don’t have to fear condensation on our coldest exterior surfaces, which we modeled to be the windowsill areas. On the downside, this “flush” option bypasses energy recovery, and will “waste” energy when flushing.

Another R&D aspect is that we hope to better understand utility modeling in operating high-density passive house buildings. We’re installing a significant array of monitoring equipment, designed by Bright Power, with input from Phius and SWA, into the building systems that will give us readings on many aspects of passive house operation, notably energy consumptions of the end users, various pumps, fans, lights, elevators, then temperature readings along with their thermostat settings as well as relative humidity levels in each individual unit and hot water consumption and gas meter readings (the hot water heaters are gas-fired). We’re all hoping to get important data for both operation of this building as well as potential design or modeling refinements for future passive house projects. The intent is to share this data with passive house organizations as well as NYSERDA and potentially other research teams.

The site used to be occupied by a landmarked public school before the City demolished it and released a Request for Proposals to develop affordable housing in its place. Located on the lower end of Grand Concourse, a prominent grand boulevard of the Bronx, on a crest, the school used to be referred to as the Castle on the Hill. We wanted to not forget about the past and the location and opted for a building that would both mark a prominent entrance to the Grand Concourse, but also bring back an educational component to the site. 

Now, the City University of New York’s Hostos Community College will run a number of student services from our building base, including a much-anticipated academic acceleration program. We’re also hosting an urgent care center, a smaller cultural space and a supermarket in the base – that’s what is really needed in the neighborhood that’s turning more and more residential.

The residential portion of the building is referred to as affordable housing, but what’s truly interesting here is that we will have a full range of income levels from formerly homeless families all the way to what’s considered market-rate in this area. All apartments will have the same features and finishes and are truly mixed throughout the floors.

Yes, we’re planning to provide our tenants with what we call a “dashboard” – an online platform designed by Bright Power where tenants can review their current energy consumption and temperature and compare it with the average building readings – pretty much in live mode. 

Hopefully, some tenants will take away more awareness about energy use in their daily activities. Maybe we’ll add some features explaining the heating and cooling systems for interested tenants, but ideally nobody should even notice that this building is anything different from what a building should be – a comfortable, quiet and healthy living environment