Apr 15, 2024

CASE STUDY: Award-Winning Multifamily Phius Project

Project Background 

Starting in March 2020, Center for Energy and Environment’s (CEE) New Homes team helped the Verdant Apartments, an 82-unit affordable housing building in St. Paul, achieve the Passive House Institute U.S. certification (Phius+). This is the first Phius+ certified multifamily building in St. Paul, and only the second in all of Minnesota. This building is 93,010 square feet and during final testing, was tighter (at 3200 cfm50 total air leakage) than many existing single-family homes. The project officially received the Phius+ certification in 2022, and in 2023 won Best Affordable Housing project at the 2023 Phius Passive Projects Design Competition.  

Inspection and Testing

CEE played a crucial role in helping this project reach the Phius+ certification by providing recommendations early in the building process to maximize efficiency throughout the building, and CEE’s in-house Phius+ rater, Jake Selstad, performed testing and verification throughout the process to ensure the building was on track to achieve Phius+ certification. To meet all certification requirements, CEE helped prepare the building by ensuring all pre-requisite certifications would also be achieved (EPA’s ENERGY STAR and Indoor airPlus and DOE’s Zero Energy Ready Homes).  

During construction, CEE performed frequent insulation inspections, mid-construction blower door tests, air leakage test of the HVAC ductwork, and assisted with testing and balancing the whole building Energy Recovery Ventilation Unit. Towards the end of construction, CEE performed final testing and verification to ensure the project met or exceeded all the stringent performance targets of Phius+. Once final testing was completed, the project was submitted to a third-party verification through the RESENET and Phius quality assurance teams. After the third-party verification process was complete, the building received Phius+, Energy Star Multifamily New Construction, EPA Indoor airPLUS, and DOE Net Zero Ready Homes certifications.  

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Case Summary

Certifications and Ratings

  • Phius+ 2018 Passive House Building Standard (Version 2.1)
  • DOE Net Zero Energy Ready Homes
  • EPA Indoor airPLUS
  • Energy Star Multifamily New Construction
  • HERS Score average (per apartment unit): 33
  • Air tightness (total building): 0.036 cfm50/ft2 surface area or .177 ACH50 (residential code for buildings three  stories or less is 3.0ACH50)

Energy Efficient Features

  • Super air-tight construction
  • Minimal thermal bridging
  • Increased R-values on all building assemblies
  • Double-framed wall for increased R-value (R-38 for total wall assembly includes R-23 batts plus continuous R15 on the inside) and minimally separated to, prevent thermal bridging while lowering the risk of moisture damage through carefully designed vapor control lay.
  • Triple-pane windows (U-Value: 0.15) for improved comfort and energy performance.
  • Energy recovery ventilation providing 7,000 cfm of fresh air to living spaces and extracting the same amount from pollution sources like kitchens and bathrooms. All 7,000 cfm is distributed to 82 units and common spaces.
  • Water loop heat pumps in dwelling units, served by high-efficient condensing boilers and an evaporative cooling tower.
  • High thermal efficiency condensing water heaters providing domestic hot water through a demand-based recirculation system.
  • All appliances Energy Star rated


  • Phius
  • Sherman Associates
  • Frana Companies
  • Kaas Wilson Architects
  • Cain Thomas Associates, Inc
  • Precipitate: Architecture, Planning, Research
  • City of St. Paul - Government