Passive House Plus certification requires a building to use only 45 kWh/m2a for heating while generating 60 kWh/m2a of on-site renewable energy (referred to as “Primary Renewable Energy – with the acronym PER).* This article is about a whole home renovation in Brooklyn, NY that was the first in the US to achieve Passive House Plus certification.
I came across this beautiful renovated home in Brooklyn, New York on BowerBird and was happily surprised to discover that it had been certified, not just Passive House, but Passive House Plus. Given that the home had been completely gutted with a third floor and rear addition added that doubled its overall living space, it was heartening to see that achieving superior energy efficiency does not have to come at the expense of light, spaciousness, or design.
Indeed, if you were to visit this home, despite its size, you might be surprised to discover that it is an energy sipper. Its south-facing rear windows allow plenty of sun to enter the living space. One of the most stunning features of the addition is the two-story stairwell from the lower-level to the new kitchen, allowing tons of natural light to flood in during the day.
The addition of the third story office provided the roof on which to add a solar array which generates a substantial amount of the home’s overall electricity needs. Conveniently, it also provides a canopy to protect the outdoor roof deck from heating the third-floor area and allowing the doors to stay open during a summer rainstorm (see feature photo above).
There is always this paradox in Passive House building of wanting passive solar heat gain in winter and preventing that same heat gain in the summer. Incorporating massive windows into this building envelope requires the use of specialized windows that prevent as much heat transfer as possible. The windows and sliding doors are from Zola windows – a California-based passive house window specialist. The windows are triple-glazed, meaning they have three layers of glass in them, with insulating gas between each pane.
Zola was able to maintain the heritage look on the street-facing windows using wood simulated double-hung windows. Rear windows are all aluminum-clad windows, some fixed, some casement, that have been treated to minimize solar heat gain in the summer.
Sliding glass doors out the back permit plenty of fresh air to circulate through the house on pleasant days while creating a seamless inside-outside feeling between the interior and exterior living areas when open.
How Was Passive House Plus Certification Achieved?
The clients were interested in creating a low-impact, low maintenance home that had fresh and healthy indoor air. The architects, Baxt Ingui Architects, who had built to Passive House standard before, suggested they build to Passive House Plus. From there, it was just a matter of working with the clients and the builder to ensure that the right materials were chosen and installed correctly to achieve a low-maintenance, low running-cost home.
The building shell
High-quality, durable materials and careful monitoring during the building process are essential to achieving what BIA refers to as a thermos of comfort for the homeowners. Because it’s a townhouse, the walls attached to its neighbours do not need any additional insulation so the interior width is preserved. The rest of the building has been insulated as follows:
- Exterior front and rear above-grade walls were insulated to R-25
- Roof insulated to R-60
- Basement sub-floor to R-26
- Below-grade walls to R-15
In order to achieve passive house certification, BIA consulted with the Passive House Academy, based in Ireland, daily. This consultation was especially important whenever design tweaks were made which affected the building envelope.
While the building was being renovated 2-3 energy audits were done to ensure that the envelope had been thoroughly covered with insulation and there no leaks around the window frames and doors after installation.
Heating, Cooling and Ventilation
Passive House requires that the house be able to function without a traditional furnace or boiler. In this case, the architects specified a Mitsubishi mini-split system for heating and cooling. In addition to this system, the fireplace in the living room was preserved while an insulated glass door was added to prevent heat escape and provide heat when in use. Another fireplace was added to the third-floor office addition.
A proper ventilation system is required as well because these buildings are so tight. Stale warm air and moist air is exhausted to the exterior while warming cool incoming fresh air through a heat or energy recovery ventilator (H/ERV). Here, they are using two Zehnder ERVs which also exhaust air from the bathrooms.
Passive House Plus requires on-site eletricity generation that provides more energy than the home uses for heating and cooling. BIA chose Brooklyn Solar Works to provide the 7 kW solar array on the roof. They designed the panels so that they double as a canopy for shading the deck and south facing sliding doors. There is no home battery to store excess energy as they were not permitted within city limits at time of build in 2015.
The incremental cost of building a Passive House certified home versus a home built to code decreases as the size of the project increases. Will Conner, an associate with BIA, who answered my neverending questions about the project, said that where you build (ie., New York City) is what typically drives the cost of the project more so than building the house to be Passive or Passive Plus (i.e. insulation, windows, energy audits).
BIA has built several homes in New York City and surrounding area and through their experience they’ve learned that there is no “one size fits all” to achieve a successful Passive House project. The key is working closely with the builder and the clients and assessing each location for its attributes and limitations.
Is Passive House Plus possible in any location?
This home was ideally situated with a south-facing rear addition that allowed for solar panels on the roof. Further, having the ability to build a new roof was fortunate because it could be designed for the panels. In tight urban centres, depending on where buildings are located, generating a building’s own electricity will not be realistic….but extra insulation and high-performing windows are always possible – it’s sometimes just a matter of priorities.
As more architects become familiar with designing Passive House homes and more builders become familiar with how to build them, we can continue to decrease our homes’ energy use and greenhouse gas emissions by building tighter building envelopes.
According to a report coming out of Germany, one of the best ways to reduce our overall CO2 emissions is to improve a home’s energy efficiency. Passive House certification offers an excellent way to accomplish that – and local building codes should require new builds and large renovations to insulate to Passive House levels.
Many thanks to Martha Valencia-Cordoba at Baxt Ingui Architects for taking time to assist me with my questions about the project.
Photographs by John Muggenborg
* Passive House certification is transitioning towards using “primary renewable energy” instead of “energy demand” to encourage the use of on-site renewable energy generation. There are three Passive House tiers: Classic, Plus and Premium, which require increasingly stricter energy standards with each tier. Visit the Passive House Institute website for more information.