Authored by Elizabeth Turner, December 15, 2016

Passive house design goes beyond typical energy reduction improvements to maximize savings on energy bills and provide a high quality, comfortable environment for occupants. Aggressive improvements to the building envelope (insulation, air sealing, windows, and relationship to sun) enable a smaller and smarter mechanical system to meet heating and cooling demand.

Advocates of design for high performance and low energy consumption for 25 years, LHB recognizes that the rigorous and tested methodology of the passive house standard is integral to surpassing increasingly-stringent codes and meeting client demands for significant energy savings. Our region has been a leader in the passive house movement, with the Waldsee BioHaus near Bemidji (2006) the first certified Passive House in the US, and Passive House in the Woods raising awareness through a detailed blog and public tours.

This year I went through training to become a Certified Passive House Consultant (CPHC) through the Passive House Institute – United States (PHIUS) and have had the opportunity to perform preliminary feasibility analysis for two multifamily projects here in Minnesota. Following are the highlights of what I’ve learned so far.


CPHC Training Cohort in Boston, Spring 2016. Photo courtesy Yanel de Angel.

Passive design centers on five key principles:

  • Minimize Loss and Gain of Heat
  • Airtight Construction
  • Optimized Windows and Solar Gains
  • Balanced Ventilation
  • Minimized Mechanical Systems

PHIUS has developed a new climate-optimized rating system
The passive house movement began in the United States and Canada during the 1970s energy crisis, and continued to develop in Germany in the late 1980s, where the Passive House Institute (PHI) was founded. Unfortunately, the US certifying organization, PHIUS, recently split from PHI. While a setback for the unity of passive building movement, one positive outcome was the development of a new standard, PHIUS+ 2015, which includes key changes from the previous PHI standard. Both programs share the ultimate goal of improving the performance of building envelopes grounded in building science but take different approaches.

While the PHI standard has a singular target for heating and cooling demand regardless of project location, the PHIUS+ 2015 standard has developed climate-specific targets. Funded through a Department of Energy grant, PHIUS collaborated with Building Science Corporation and NREL to study the “sweet spots” of cost and impact of heating and cooling energy demand for more than 100 climates. Find the targets for your project site through this interactive map.

To achieve PHIUS+ 2015 certification, all projects must meet the heating and cooling targets for their location in addition to universal targets for primary energy use per person and airtightness of the building envelope. This change allows project teams to take a more creative and place-based approach to meeting universal goals.

While the PHIUS+ 2015 heating demand target is less rigorous for the Minnesota climate than the PHI target, this change makes certification more feasible and accessible. We see these cost-optimized standards as an excellent opportunity to utilize progressive building science methodology to greatly improve the energy performance of our affordable housing projects (60-85% better than code at a 0-3% cost premium), making the most efficient use of available funds and impacting a greater number of residents.

It’s not just for single-family homes
Though the PHIUS certified project database contains mostly single family homes, it also lists many projects that are multifamily housing and other project types, including the Orchards at Orenco, a 57-unit complex in Oregon. In Europe, commercial and multifamily projects have been applying passive standards for many years. Affordable housing funders are increasingly incentivizing multifamily projects seeking certification, including the Pennsylvania Housing Finance Agency, where in 2016 27 out of 94 projects intended to pursue certification, and ten of those were awarded tax credits. Moving forward, many suggest that the term passive building is more inclusive and accurate than passive house as we work to utilize these rigorous design standards across a broad range of project types.


Working model of affordable multifamily housing in WUFI Passive with project performance indicated at right, including climate-specific heating and cooling goals

High performance hinges on high-quality modeling and verification
PHIUS has collaborated with Fraunhaufer to develop an energy modeling program, WUFI Passive, based on the PHI Passive House Planning Package (PHPP). This software allows the Certified Passive House Consultant (CPHC) to optimize the design by testing the performance of building geometry and components, from insulation and window types to length of hot water pipe and heating system specifics. To avoid potential moisture issues in an extremely air-tight building, the project can be analyzed through embedded WUFI software.

This integration between envelope, mechanical systems, and building use enables project teams to determine the best way to achieve the PHIUS+ standard. Third-party verification through a PHIUS+ Certified Rater ensures that the energy model accurately represents the project as built and guarantees a level of construction excellence for the owner.

If you are interested in learning more about how the PHIUS+ 2015 standards can add value through high performance and comfort, we’d love to start the conversation!


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