Phius Consulting: a Success Story in the Making

March 20, 2024

What An Architect DoesAirtightnessEco DesignFrom the FieldPassive House Architecture

One of TBDA’s services is energy modeling and design support for Owner/Architect teams seeking Phius certification on larger projects. This 44-unit apartment building (a mix of affordable and market-rate) is our most significant consulting project so far, and we wanted to share some of the successful aspects.



First and foremost, leadership from the owner to build the team is critical–the bigger the building and team, the more important it is that everyone is aligned to deliver an exceptional result. David Pope’s leadership at Oak Park Residence Corporation, with Cullen CM as owner’s rep alongside, has been outstanding–communication is excellent, and the focus on goals is therefore constant. We’ve kept up weekly meetings throughout the process, and it’s been key to success. That communication enabled Ware Malcomb, the architect, to come up to speed quickly on Passive design, and for Synergy Group, the contractor, to participate in discussions about materials and constructability of air barriers, railing systems, the solar array, and so many other decisions. Synergy also took Phius Builders Training, a great help for in-the-field knowledge.


Rater/Verifier Input:

One of the eye-openers for us was how important early involvement of the third-party Rater/Verifier was. TBDA has designed many Phius certified projects, mostly smaller single family, up to 3-flats, in which we typically design HVAC as well as structure and architecture. Addressing the issues that come up with the rater during construction is therefore simple. But with a team this size on a much more complex building, having EcoAchievers at the table to work through how various field testing and verifications would fold into the construction process was crucial to good flow. They also have much valuable experience with multifamily-specific design and construction issues relevant to Phius. Now that we’re well underway with construction (air barrier testing in the next few weeks), their quality control inspections of insulation, membranes, and submittals ensures that what’s built will perform as designed.


Designing for Phius:

The design phase is where our main input happens. In this case, we worked with the design team through iterations of window sizes, insulation levels, shading, and balcony configurations to find the sweet spot. Phius uses metrics sensitive to both climate and building density, which set our energy modeling targets. It was fascinating to see that too much glazing (over about 28% window-to-wall) made the metrics nearly impossible, but once we got the glazing to a reasonable level, we actually had to moderate the insulation levels: given the high internal gains (lots of people and appliances/lighting per square foot), we had to find a balance between heating and cooling energy. Too much insulation and the cooling energy was too high; too much shading and the heating energy could dip just below the threshold. As we got deeper into the design, we reviewed the window specs, insulation types, and air barrier transitions, calculated the thermal bridges of balconies and other connections, and helped conceive of the rooftop and south facade solar array.


Since this project received a grant from the Illinois Clean Energy Community Foundation, an important proof of success will be demonstrating net zero energy on-site over a 12-month period. A significant portion of the grant disbursement relies on achieving this, which will mean that resident behavior, mechanical system performance, and the weather will need to, on average, get along! With a certified Phius building, though, we stand the best chance of achieving that goal, since Phius’ scrutiny of the energy model and EcoAchievers’ site verification provide quality control. 


Stay tuned for upcoming tours and presentations on this important project!