Passive House Retrofit: Making the Case to Brooklyn Cohousing

by Ken Levenson*.

My client, Brooklyn Cohousing, is an intentional community of 20 families developing a 30 unit, 34,000 s.f. condominium. We were discussing sustainable design priorities. They were eager to suggest solar photovoltaic panels, green roofs and geothermal heat pump systems.  And why not?  The public imagination has defined green building through these systems, and they are exciting. The Sears tower is going to have windmills on it, how awesome is that?

That said, I wanted to introduce my clients to Passive House, a sustainable approach to building that turns these assumed priorities on their head by insisting that we return to the basics of building.  I was nervous. Would they go for it?

Passive House, after all, is not an incremental improvement. It's huge. Passive House reduces heating and cooling energy requirements by up to 90%, a standard it meets without the aid of renewables or new technologies. Our clients were excited by the possibility but also skeptical. They wanted  to know how those lofty goals could be attainable. I set out to explain. The following is the first of two brief overviews of the Passive House as I described it to Brooklyn Co-housing in preparation for our project together.

Simply put, Passive House is the most rigorous energy standard today.   Passive House methodology focuses on cost-effectively optimizing, in a truly integrated and highly controlled and predictable manner, those building elements essential to providing thermal/environmental comfort: the exterior (building) envelope and ventilation systems.

Passive House was developed in Germany in the 1990s and codified in the Passive House Planning Package (PHPP), produced by the Passivhaus Institut (PHI) in Darmstadt Germany.  From the start, the authors of Passive House, Bo Adamson and Wolfgang Feist, sought wide public acceptance. They therefore prioritized affordability and comfort as much as energy efficiency. Passive Houses are meant to be truly affordable, and the most comfortable homes around.

In order to be certified as a Passive House, a building must meet 3 very stringent standards, as established by PHI or the Passive House Institute US (PHIUS) based in Urbana, Illinois.

1)     An Airtight building shell ≤ 0.6 air-changes per hour (ACH) @ 50 pascal pressure.
2)     Annual heat requirement ≤ 15 kWh/m2/year. (4.75 kBTU/(sf/year), or approximately a tenth of typical home heating requirement.
3)     Primary Energy ≤ 120 kWh/m2/year.  (38.0 kBTU/(sf/year). Or approximately 55% of typical home primary energy use.

Greater efficiencies are possible, but are driven by occupant behavior and not the building envelope - such as appliance and artificial lighting usage.

In order to be deemed a "Passive House" a building must be certified. The certification process is not expensive, and is intended to maintain quality control for buildings using Passive House label.  To help projects successfully navigate the requirements, PHIUS trains certified Passive House consultants.  (I am currently in the middle of this training and we have hired a certified consultant to help us in the meantime. For those interested, a schedule of upcoming trainings is listed on PHIUS' website.)  As the PHPP Introduction states (in unmistakable translation from German): "Simply combining appropriate components is not sufficient to construct a building as a Passive House - the integration as a whole is greater than the sum of the individual parts. The Component interaction necessitates an integral plan in order to achieve the Passive House Standard. This is the purpose of this Passive House Package."

Passive House reduces the actual energy load for a building, a positive step for the environment that drastically reduces energy related costs for the occupants.  For this reason, it seemed the ideal solution for Brooklyn co-housing. Yes, Brooklyn Co-housing will still look to put PV on the building - but in the future, when it costs less.  And when it does, Brooklyn Co-housing can readily and afford ably make their home a zero energy building.   But the first priority today will be a well-built building.   That's exciting.

* Ken Levenson is a partner in Levenson McDavid Architects P.C., in Brooklyn, NY. Ken also maintains the blog Checklist Toward Zero Carbon.