The Perlita Passive House Journey Part II: Architectural and Engineering Design Strategies
By Sofia Siegel
As you know from Part I of this blog series (or, if you haven’t read it yet, check it out here!), Xavier Gaucher is galvanizing the Los Angeles Green Building community through the use of his own single-family residence, The Perlita Passive House, as a case study to promote Passive House design and inspire others.
Passive House, outlined in Part I, is design driven and performance verified; this non-prescriptive style makes Passive House easy to modify for a project’s various needs, but the required performance results are quite rigorous, and challenging to achieve.
Gaucher’s architectural and engineering strategies began with the basics. The first step to ensure a building’s efficiency is creating a high-performance envelope. Insulate insulate insulate! This reduces heat loss in the winter, and heat gain in the summer (and, much of spring and fall in Los Angeles), which leads to comfortable interior surface temperatures without the need for energy-hungry HVAC systems. From there, it is crucial to make sure that the envelope is airtight. This reduces drafts, and the potential for moisture damage (a real problem in damper climates, but still relevant in arid Southern California during the rainy season). It also cuts down on heat loss (winter), heat gain (summer) and humidity when applicable.
In the Perlita House, this airtight seal was achieved with the use of a membrane product, and Gaucher hosted an on-site demonstration of a Blower Door test to identify any possible leakage at this stage. This plastic sheeting process is installed in coordination with CertainTeed fiberglass insulation, in wall or ceiling cavities, and is specifically intended for our local climate. The Blower Door test revealed some leaks, which were addressed before closing and finishing the walls (at which point even the most basic repairs are prohibitively costly to make).
Here you can see the membrane product (left), and the Blower Door testing (right)
Gaucher targeted thermal bridges, or the areas in the home with significantly higher heat transfer than surrounding materials, as the next strategy to minimize energy loss. What good is an airtight envelope if the metal ties in your cavity walls are siphoning heat outside through the walls (or bringing in heat during the hottest months)? These problem spots reduce energy efficiency and allow condensation to form (leading to hard-to-treat mold problems, and thermal discomfort). These strategies are multi-dimensional and often include redundancies to best reduce unwanted heat loss or gain.
The next step in designing the Perlita Passive House was optimizing the windows and shading.
What makes a window perform?
Glass. Frame. Spacer. Install.
The project installed high efficiency and airtight double-pane windows for optimal thermal regulation (triple-pane windows in the Mediterranean Climate of our project site provides diminishing returns over the double-pane option, at a higher cost). A thermally broken frame contains a barrier between the inside and outside panes that will prevent conductive thermal energy loss—a low conductivity material (the spacer) is placed inside this barrier, around the perimeter of the glazing. And of course, the installation can make-or-break it. All the hard work and energy-conscious planning goes out the window if installation is not air-tight!
Continuous ventilation plays a huge role in the final comfort level in the home. By bringing in filtered, fresh air year-round, the project will help eliminate indoor pollutants. It reduces heat loss in winter, and humidity in the summer (Perlita House is in a climate that will require heat recovery as well). The difference in comfort in a continuously ventilated space is staggering, and not just due to temperature.
Bringing in constant fresh air helps manage Carbon Dioxide levels and keep Indoor Air Quality safe and healthy. A traditionally designed (read: dated) building will show huge leaps in amounts of indoor CO2 levels during the day, leading to periods of time when occupants suffer from the negative effects of CO2 (reduced cognitive performance being amongst the most alarming).
With these five design components considered, a Passive House still needs to meet the rigorous performance requirements outlined by the low-energy design standard. Peak heating and cooling demand, and peak heating / cooling load are hard (if not impossible) to meet without close attention to insulation, air-tightness, and ventilation. The Blower Door tests were required to ensure air-tightness (n50 < 0.6 ACH to achieve compliance), and total primary energy consumption must be limited to < 38 BTU/hr.ft². Performance will be revealed once the Gaucher family moves in, but proper envelope design and efficient appliances and features put the home on the correct path, and we are optimistic about the results!
Construction is now well underway, and we anticipate completion in September. Throughout the process, Gaucher remains active in the space, leading trainings and hosting open-house style demonstrations of various process points, including an on-site demonstration of a Blower Door test to verify leakage in the building envelope. Additionally, Xavier and Verdical Group’s Sofia Siegel spoke together at the Dwell on Design Conference in Los Angeles on June 25, which attracts 20,000+ design-savvy attendees annually.