The First Phius Retrofit in Georgia

Several years ago, when we decided to build a passive house in Atlanta, we were unaware that we were the first in Georgia to embark on this journey. We hoped that others had already gone down this path, so we could seek their advice and learn from their experience. Nevertheless, we were excited to be trailblazers for passive house construction in Georgia, having previously built to other green building standards.

Initially, we followed the Phius Prescriptive Path, which involved following all the prompts on the checklist to ensure compliance with the standard. Unfortunately, we had already designed the house and obtained a building permit, making it challenging to adjust the design to comply with Phius requirements. A structural redesign would require us to obtain a variance and return to the City for a new permit, which was not an ideal option. Thus, we opted for the performance path, which required a WUFI Passive analysis.

Our architect and energy consultant for the project, LG Squared, developed the overall design, performance details, and HVAC design. Chris and Jodi Laumer-Giddens were experienced in building homes similar to Phius, with the "Perfect Wall" assembly being a standard detail in most of their designs. Given our building science experience, we knew there would be trade-offs involved. We already understood the value of insulation and air sealing, as we incorporated these features in all our projects. However, going through the WUFI analysis revealed a few unexpected learnings.

We discovered that having a fastener with some thermal resistance is essential. For instance, changing the specification from a galvanized to a stainless steel fastener saved one inch of insulation in the modeling. Depending on the modeling for a particular house, such trade-offs can save on labor costs by reducing the layers from two insulation layers to only one layer in addition to the extra insulation cost. The model demonstrated that a plastic screw would be even better, although we were still looking for one long enough for our application.

We also learned the significance of passive solar design within a Phius project, particularly in this climate zone. A low solar heat gain coefficient in Atlanta is essential to block out the sun's rays and reduce the air conditioning load. However, our WUFI analysis required a high solar heat gain coefficient to reduce the heating load in winter and take advantage of the sun's energy. Failure to do this would have necessitated the addition of several extra inches of insulation. We may need to install solar screens during the summer if any windows receive direct sunlight. Fortunately, deciduous trees around should block out the direct sunlight during the summer while still allowing the sun to heat the house when the leaves have fallen.

Atlanta's unique climate zone, with similar or equal heating degree days and cooling degree days, requires a balance in the window design and building envelope for heating and cooling simultaneously. In Florida, for instance, one designs for hot and humid weather, while in New England, one designs for cold weather. However, given the location and elevation in Atlanta, we have mixed weather conditions that demand a balance in the design for heating and cooling equally.

Even so, our Phius-qualified window, which helps our clients save on operating costs, does not meet Georgia's energy code for windows and doors. If one chooses to use the prescriptive path, one may spend more on materials and labor than on the performance path. We are still calculating the differences and will share our findings with Phius to help establish a foothold in the Southeast United States.

We welcome anyone interested in our Phius project to join us at #1920sMakeoverATL, where we will discuss the design, project partners, materials used, and lessons learned.