When the February 2021 winter storm plunged Texas into a multiday power crisis, millions of households faced freezing indoor temperatures. Pipes burst, homes dipped below 40 degrees Fahrenheit, and dozens of people lost their lives. Yet one house in Austin never fell below 49 degrees indoors despite losing power for three consecutive days. That house was built to Passive House standards, and its performance offers powerful lessons about the value of deep energy retrofit construction in an era of increasingly extreme weather. This article examines the story of Trey Farmer and Adrienne Lee Farmer, who converted a drafty 1914 Craftsman bungalow into a certified Passive House, and how that decision proved critical when the grid failed.
The Story Behind the Texas Passive House Project
Trey Farmer, a licensed architect with Forge Craft Architecture + Design and a certified Passive House consultant, and his wife Adrienne, a designer with Studio Ferme, originally lived in a 1,430-square-foot Craftsman-style bungalow built around 1914. The home sat a few miles west of downtown Austin near a train line and a major highway. With a new baby in their lives, the couple became acutely aware of the home’s shortcomings. The original structure had no subfloor, minimal insulation, and such extensive termite damage and wood rot that the framing no longer met code. Despite wanting to preserve the original character, they discovered they had to essentially rebuild the house in place.
The Farmers chose to rebuild to Passive House standards, working with architect Hugh Jefferson Randolph during the early design phase. They kept the original east-west orientation and the original footprint, adding 670 square feet onto the back for a total of 2,100 square feet. The front facade maintained the original Craftsman charm with careful detailing, while the rear of the house adopted a contemporary flat-roof style with large windows capturing downtown views. This approach kept permitting simpler and preserved the neighborhood character. For those considering a similar approach, the Passive House design and construction lessons from the R House project offer additional insight into balancing historic preservation with high-performance building standards. The family moved out for 14 months and returned to their completed Passive House in mid-February 2020.
Key Passive House Features and Building Envelope Strategies
The Farmers’ home incorporates several features that together create a high-performance building envelope. Continuous insulation was a top priority. The walls received R-30 insulation, double the local code requirement, using Rockwool batts on the interior side combined with Zip System integrated sheathing rated at R-6 on the exterior. Triple-pane windows replaced the original single-pane units, far exceeding the double-pane windows that meet standard Texas code. According to Passive House Accelerator’s overview of what and why of Passive House, these strategies form the foundation of the standard’s energy performance targets.
The home’s mechanical systems are equally refined. A 6,500-watt solar array sits on the southern roof face, though without battery backup the system cannot operate during a grid outage. The home uses all-electric appliances, including a heat pump water heater located inside conditioned space. An energy recovery ventilator (ERV) continuously supplies filtered, tempered fresh air while capturing heat from exhaust air. The Farmers also installed a dedicated dehumidifier, which Trey specifies for all his Austin projects given the region’s hot, humid climate. Below is a summary of the key building envelope specifications:
| Building Component | Passive House Specification | Typical Texas Code Requirement |
|---|---|---|
| Wall insulation | R-30 continuous (Rockwool batts + Zip R-6 sheathing) | R-15 (approx.) |
| Windows | Triple-pane, high-performance | Double-pane |
| Airtightness | 0.6 air changes per hour (ACH) | 5 ACH |
| Ventilation | ERV with continuous filtered fresh air | None required by code |
| Water heating | Heat pump water heater in conditioned space | Standard electric or gas |
| Renewable energy | 6,500 W solar array (no battery backup) | Not required |
Adapting Passive House Standards for a Texas Climate
Passive House standards are often associated with cold European climates, but the principles apply equally well in hot and humid regions like central Texas. The Passive House concept is fundamentally about energy use targets rather than prescribing specific construction methods. Builders model their house in 3D including all window parameters, wall and roof assemblies, HVAC systems, and appliances. The model predicts annual energy consumption and verifies whether the design meets the required heating and cooling demand targets.
Airtightness is the aspect of Passive House construction that Trey Farmer describes as the most foreign to the Texas building market. Austin’s climate zone currently allows up to five air changes per hour (ACH) under code, while other parts of Texas and much of the country require three ACH. Passive House standards demand 0.6 ACH, nearly ten times tighter than Austin’s baseline. Trey explains that once you achieve two to one ACH, you realize substantial energy savings because you are no longer leaking heated or cooled air through the building envelope. At the Passive House level of 0.6 ACH, an additional benefit emerges: dust, pollutants, and allergens cannot enter through gaps and cracks, creating a measurable improvement in indoor air quality.
The ERV plays a critical role in this system. Because the home is so airtight, mechanical ventilation is essential. The ERV runs continuously, bringing in fresh outside air that is filtered and preconditioned using the energy from outgoing stale air. This means the Farmers are not paying the energy penalty that would normally come from conditioning hot, humid Austin air. The dedicated dehumidifier further manages moisture, an important consideration in a climate where summertime humidity can overwhelm even a well-sealed envelope.
How the Farmers’ Home Performed During the 2021 Deep Freeze
In mid-February 2021, a polar vortex sent multiple storms tracking across the jet stream, bringing record low temperatures to Texas. Between February 11 and February 20, three separate ice storms hit the region. On February 14, temperatures dropped into single digits, and the Electric Reliability Council of Texas (ERCOT) began rotating power outages. The Farmers had been asked to conserve energy and had set their thermostat to 68 degrees Fahrenheit. At 1:00 a.m. on Monday, the power went out.
When Trey woke that morning, outdoor temperatures had plunged to 9 degrees Fahrenheit. Inside, the house registered 62 degrees. By comparison, the identical neighboring house before its Passive House retrofit had dropped to 36 degrees indoors under the same conditions. Trey describes the difference succinctly: the neighbors “may as well have been living in a tent.” Outdoor temperatures remained below freezing for a record 144 consecutive hours. The Farmers’ home warmed slightly during daylight hours thanks to south-facing triple-pane windows capturing passive solar gain. On the second night, indoor temperatures fell to 53 degrees. The family then moved to stay with friends who still had power. A neighbor checked on the house, and according to Trey, the coldest it ever got was 49 degrees on the third day. This performance aligns directly with the Passive House design principles that prioritize envelope performance over active mechanical systems.
A February 2020 Rocky Mountain Institute study titled “Hours of Safety in Cold Weather: Framework for Considering Resilience in Building Envelope Design and Construction” examined how long a home could maintain safe indoor temperatures during a power outage. The study found that homes built to Passive House envelope standards maintained indoor temperatures above 40 degrees Fahrenheit for more than six days, significantly longer than code-compliant new buildings. The Farmers’ experience provided real-world confirmation of this research.
Passive House vs. Conventional Homes: A Performance Comparison
An informal comparison shared online during the storm highlighted the dramatic performance gap between building standards. Three Austin homes were compared, each having lost power for more than 50 hours. The first house, an 800-square-foot structure built in 1919 with single-pane windows, balloon framing, and no wall insulation (though it had R-80 attic insulation and R-20 floor insulation), dropped below 40 degrees within five hours and hovered around 31 degrees. The second house, a 2,300-square-foot home built to 2009 code with standard spray foam insulation, no attic, and a sealed crawl space, dropped below 40 degrees within 48 hours. Its occupants could only maintain temperatures in the 50s by running gas burners at full blast. The third house was the Farmers’ 2,100-square-foot Passive House, which never dropped below 49 degrees throughout the entire outage.
The comparison underscores a critical point: Passive House construction provides a safety margin that standard building codes do not. During a grid failure, that margin can mean the difference between sheltering in place and evacuating. Trey monitored his home using Airthings sensors that tracked temperature, humidity, carbon dioxide, radon, VOCs, and particulate matter. During the first night with no power, the family of three plus their dog slept behind a closed bedroom door. Carbon dioxide levels reached 3,270 parts per billion, well below the OSHA limit of 5,000 ppb and comparable to typical airplane cabin levels. The rest of the house never exceeded 1,200 ppb. This data illustrates how even in a compromised situation, the Passive House maintained acceptable indoor environmental quality. For those interested in the broader landscape of high-performance building, a review of various green building certification programs including LEED, Energy Star, and net-zero standards provides useful context for how Passive House compares with other approaches.
Lessons for Resilient Home Design
The Farmers’ experience offers several takeaways for homeowners, builders, and policymakers. First, building envelope performance is the most reliable path to passive survivability during a power outage. Insulation, airtightness, and high-performance windows do not require fuel or electricity to work; they slow heat loss passively. Second, the all-electric nature of the home created a trade-off during the outage. Without gas appliances, the Farmers could not boil water for warmth or cooking. However, hospitals in Houston reported over 300 carbon monoxide poisoning cases from people using gas stoves for heat, illustrating that gas reliance carries its own dangers. Battery backup for the solar array would have allowed the Farmers to island their home and draw stored power during the grid failure, a lesson for future projects.
Trey Farmer views the experience as a successful proof of concept for passive survivability. The house performed well under extreme conditions that most code-built homes could not match. As climate change increases the frequency and severity of extreme weather events, the gap between standard construction and high-performance building becomes more consequential. The techniques used in this project from continuous insulation to airtightness detailing are well documented. For builders seeking construction-level guidance, Passive House framing techniques for energy efficiency with double-stud walls offer a practical starting point for achieving these performance targets in new construction or deep retrofits. The Farmers’ Craftsman bungalow demonstrates that resilient design does not require sacrificing aesthetics or historic character; it simply demands a commitment to building better.