Case Study: EnerPHit in NYC

Just days before last week’s Case Study on Passive House retrofits, the New York Times lauded the significant number of large PH projects underway in the NYC region and how these are “catching the attention of our city officials.” Indeed, city officials made up a significant portion of the standing-room-only crowd at our event co-sponsored by AIANY and New York Passive House at the Center for Architecture.

The Case Study looked at a Brooklyn brownstone currently seeking EnerPHit certification, the Passive House standard for retrofits. Presented by owner and architect Jane Sanders  and builder Jeremy Shannon (Build with Prospect, Inc.), this full gut renovation provided a perfect opportunity to prepare the century-old building for the next 100 years by integrating Passive House’s principles of air tightness, continuous insulation, and whole-house heat recovery ventilation. Shannon pointed out the three pathways that one might approach for Passive House refurbishment like theirs:

  1. Retrofit to the same Passive House standard as new construction projects, which requires a maximum space heating demand of 4.75 kBtu/ft2 per year.
  2. Retrofit to the EnerPHit standard, which raises maximum space heating demand to 7.92 kBtu/ft2 per year to account for thermal bridges and other features that are often intrinsic to existing buildings.
  3. Pursue “EnerPHit + i” (also known as “component certification”), a step-by-step method for certifying the design, installation and verification of specific building components, such as windows, roof insulation over the course of a project.

The brownstone team chose option 2. However, because retrofit projects often move along in phases—replacing building components like windows and walls as necessary or when a component has reached its useful lifespan—option 3 can be attractive and more affordable. The Passive House Institute is currently conducting research with manufacturers and designers to develop templates for building component certification, as well as ways to certify a “refurbishment plan” that models a project’s specific EnerPHit strategy.

It was pointed out that New York row houses are particularly good candidates for either full or phased EnerPHit renovation because their largest surfaces, the party walls, typically face the conditioned space of neighboring buildings, which reduces the amount of exposed surface area requiring insulation. A thin layer of cement coating and a liquid-applied air barrier are all that is needed at the party walls, meaning no interior space loss on the sides.

These improvements to the building envelope drastically reduce heating and cooling requirements to the entire house. Sanders’s home uses a single two-ton (24,000 Btu/h) two-zone heat pump system—about one-fifth the size of a typical heating system. In addition to being much smaller and more efficient than standard equipment, this also allows for more discreet heating and cooling throughout the building: ducts are concealed within walls and ceilings, and there are no radiators to be found in front of windows. In fact, it is sometimes a challenge to find heating and cooling equipment small enough to properly serve the loads of a Passive House building. Most heating boilers come only as small as 60,000 Btu/h––over four times the load of this EnerPHit candidate. At 13,000 Btu/h, it requires roughly the same power as a mid-sized window air conditioning unit.

Improvements to existing buildings form a central part of Mayor de Blasio’s One City Built to Last plan, and refurbishments like this one seem like a great place to start. EnerPHit is one of a number of ways to improve our older buildings, save money, and build a greener New York without laying a single new brick.

Thank you to our event partners AIA New York and New York Passive House.

Written in collaboration by Nadia Elrokhsy (Associate Professor of Sustainable Design, Parsons School of Design, The New School and UGC MPC volunteer) and Cramer Silkworth (Principal and Chief Engineer of Baukraft Engineering, PLLC, Adjunct Faculty at Rhode Island School of Design).

About the authors

Nadia Elrokhsy
Nadia is an Associate Professor of Sustainable Design at Parsons The New School for Design and an active member of Urban Green's Monthly Programs Committee.