The retrofitting of existing buildings is a central component of the climate action plans of virtually every city in North America.  Many of today’s buildings were constructed in an era of inexpensive fossil fuels, the impacts of which were largely unknown.  The opportunities to lower emissions by improving energy efficiency in buildings is significant and most of the simplest available measures are well understood and are regularly implemented in buildings of various types.  However, while many buildings perform efficiency upgrades to individual systems, there are limited examples of occupied buildings that perform the type of integrated retrofits that are likely needed for most cities to meet their climate action goals.  Upgrading existing buildings will require significant resources and in addition to raw efficiency must also deliver a high-quality environment, be primed for a future powered by renewable energy, and provide resiliency in the face of future climate fluctuations and crises.

The emphasis in the study is on selecting the required energy conservation measures, and how these might be phased in over time while the building is occupied.  More briefly, we will also describe code and regulatory barriers to pursuing this deep retrofit, the most important technical and market challenges, and how capital planning for such measures might be organized.  The goal of this work is providing a high-level guidance document that will allow similar such buildings to envision a phased deep retrofit of their own building in the absence of relevant examples.

Context: Building + Policy

For this study, we have selected an existing building in New York City, one typical for a large segment of the city, and analyzed what measures would be necessary to deliver the most comfortable building for the occupants while using the least amount of energy.  To analyze how to reach this dual goal of human comfort and energy efficiency we have utilized the Passive House standard for existing building retrofits: EnerPHit.

The Building

The project team selected an existing building with features and challenges common to many high-rise multifamily buildings in the region.

The building selected for study is a 15-story, market-rate residential building in Brooklyn. Constructed in 1950, the building has masonry exterior walls that enclose 163 apartments across 123,000 gross square feet. The tower is typical of a large swath of buildings in New York City (as well as many other regions) and has many of the most common challenges that will be encountered by anyone looking to perform a deep retrofit of an occupied multifamily building.


As early as 2007, the City of New York identified buildings as a critical sector in their climate action plan, PlaNYC.6 This plan resulted in the development of the Greener, Greater Buildings Plan (GGBP, 2009) which required large buildings to benchmark their annual energy and water use, and to undergo a whole building energy audit once every ten years.

In 2015, the City reaffirmed its focus on buildings with the release of OneNYC. The current climate action commitments outlined in OneNYC revolve around an aggressive goal of reducing citywide carbon emissions 80% by 2050 (“80 x 50”), using 2005 as a baseline.


The building selected for this study fits within the “Multifamily, Post-war (to 1980), greater than 7 stories” typology published in the One City: Built to Last Technical Working Group Report. The report outlines available pathways for retrofitting NYC buildings to meet the “80 X 50” target set down by Mayor De Blasio, includes, in total, 322 million square feet of building area, more than 5% of citywide building area and 15% of multifamily buildings. A rough estimate indicates that this segment houses nearly 1 million people.



The study emphasizes selecting those improvements that most effectively meet the requirements of EnerPHit, and describes ways to phase these in overtime while the building is occupied.


The primary retrofit components of achieving the EnerPHit standard for our subject building are relatively simple:

  • Replace the windows with high performance units
  • Reclad the façade with insulation and an airtight layer
  • Upgrade the ventilation to a balanced system with heat recovery
  • Replace the heating and cooling with a high efficiency system


The analysis described throughout this report was performed jointly by Steven Winter Associates in New York, New York and the Passive House Institute (PHI) in Darmstadt, Germany.  PHI are the original developers of the Passive House standard, which they continue to refine, and among many other activities administer the international network of accredited Passive House certifiers.

Multiple strategies have been explored in each category to determine the most effective solution that limits disruption to the occupants. To meet the Passive House EnerPHit criteria, analysis was done of improvement: envelope (insulation, airtightness, and windows), heating and cooling systems, ventilation, and domestic hot water systems.

  1. Envelope:
    • Roof Insulation
    • Airtightness measures (shafts, etc.)
    • EIFS and sheathing at exterior (incl. airtightness layer, and VRF risers at exterior)
    • or Rainscreen System
  2. New Passive House certified windows
  3. Heating + Cooling
    • Install VRF units (Distributed or Centralized)
      • Replace steam radiators with VR cassettes
      • connect to risers
      • Recladding
    • or High Performance Packaged Units
  4. Ventilation
    • Decentralized, semi-decentralized or centralized ERV supply
    • Return ventilation system
  5. Domestic Hot Water
    • Replace to steam exchanger with high-efficiency boiler
    • Air to water heat pumps for DWH
  6. Lighting
    • Upgrade lighting to LED
    • Install energy efficient appliances
  7. Plug + Process Loads


Although a full retrofit is the least disruptive overall, phasing has been carefully explored so that owners might align upgrades with financial or other milestones.



Proposed Retrofit Strategies Proposed Retrofit Phases
1 New windows + roof insulation + airtightness measures (shafts, etc.) Year 0 Envelope 1: windows + roof insulation
2 Centralized ERV supply & return ventilation system Year 4 Ventilation system (balanced ERV system + exhaust)
3 EIFS and sheathing at the exterior (incl. airtightness layer, and VRF risers at exterior) Year 8 Envelope 2: wall insulation & airtightness
ALT 3: Rainscreen system
4 Install VRF rooftop units, replace steam radiators with VRF cassettes, connect to risers Year 12 Replace heating/cooling systems with VRF system
ALT 4: High-performance packaged units
5 Replace domestic hot water heat exchanger with high-efficiency boiler Year 16 Replace domestic hot water boiler with high-efficiency model
6 LED lighting and controls, energy efficient elevators, EnergyStar appliances Anytime Upgrade lighting to LED, upgrade elevators, install energy efficient appliances

The good news about climate change is that it is cheaper to fix than it is to ignore.Amory Lovins, The Rocky Mountain Institute

Benefits + Costs

The benefits of a complete Passive House retrofit result in a radical transformation of the building, from improved comfort, air quality, and aesthetics, to more responsive heating and cooling systems, to far lower utility bills.


The report includes conservative estimates of costs of each phase of the proposed work.

Simple energy efficiency projects are typically evaluated by the number of years required to pay back the expenditure from utility savings. But this is an insufficient lens through which to evaluate a deep retrofit that transforms a building in almost every capacity. Instead, we should evaluate these projects based on their impact on the total value of the building.
At the same time, we should identify mechanisms to connect the overall societal benefits of these projects to the costs borne by the individual building.

The costs of the optimal retrofit are roughly 12% of the current market value of the property. New apartment buildings in the vicinity have an average sale cost that is roughly twice that of the subject building. It is clear that the retrofit described here—featuring a completely new exterior skin, vastly improved interior conditions, and highly responsive, efficient systems—would deliver an increase in market value several times greater than the costs.

Paths Forward

Moving forward we will need to incentivize the more effective delivery of retrofitted systems, whether this means creating a strong market demand for modular recladding systems or ensuring that efficient equipment such as the high performance packaged heating and cooling units.  We will also need to identify mechanisms that connect the broader societal benefits of deep retrofits with the costs to individual building owners.

A substantial percentage of our existing building stock must undergo deep, holistic retrofits if we are going to meet our climate action goals and avoid the most calamitous impacts of global climate change.  We’ve selected the Passive House pathway to inform this report because of its focus on comfortable, healthy spaces and its strong track record of delivering significant heating and cooling energy savings.  The costs are substantial, but the benefits are extensive and result in a radically transformed building of significantly higher value that will allow our community to meet its climate action goals.  Inaction is not an option.


We recommend the following path forward to build on the work of this report:

Deep Retrofit Studies:  Applying this analytical framework to multiple other building typologies.

Modular Systems Research:  Additional research to determine the feasibility of creating modular retrofit systems.

Finance and Policy Research:  Financial and policy instruments that might directly incentivize extensive and holistic retrofits.

High-Performance Systems Research:  Identify systems or products either available elsewhere, or are on the cusp of commercialization, that could significantly improve the transformation of existing buildings.

Education and Training:  Extensive education and technical training to enable high-performance retrofits to move forward at scale.

It is clear from our analysis that it is feasible to transform an occupied building of this type to meet the demands of our coming century, and while doing so producing a living environment of far higher quality than we currently experience.


Primary Author
Yetsuh Frank
Building Energy Exchange

Lead Technical Advisor
Lois Arena
Steven Winter Associates

Passive House Modeling
Jan Steiger
Passive House Institute

Cost Estimating
Greg Bauso
Monadnock Construction

Technology Support
Sam Macafee

Mike Woolsey

Ken Levenson
475 Building Supply

Joe Fox

Report Sponsors


Available For You


  • Deep Retrofits
  • Retrofit
  • Multi-Family
  • Passive House / High Performance
  • Passive House

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