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The Build

The Farmers' house sits on a corner lot near a train line and is a block away from a major highway. Trey points out that there's a lot of research showing a correlation between detrimental health effects and people living so close to freeways and freight lines, likely due to the high amount of particulate matter in the air. "Indoor air quality was a big issue for us, and the house was uncomfortable. Really hot or really cold. We had a monster AC unit outside our window that would churn on and sound like a diesel engine. It was a beautiful old house, but it didn't feel like it was safe to have a child there." For all these reasons, the Farmers chose to go the passive house route.

Trey's mentor, architect Hugh Jefferson Randolph, collaborated on the early design phase with the Farmers.

Texas Passive House Exterior Rear
Texas Passive House Exterior Rear. Photo Credit: Trey Farmer

They did not change the home's orientation, which runs east-west. They kept the original footprint and added 670 square feet onto the back. The house is now 2,100 square feet. The original façade and roofline were rebuilt, and all the detailing is the same. "[Doing this] made things easier with some of the permitting, and we wanted to keep the original charm and beauty of the Craftsman home," Trey says. The back of the house is contemporary, with a flat roof and big windows that take advantage of downtown views.

Texas Passive House, View of PV From Above
Texas Passive House, View of PV From Above. Photo Credit: Trey Farmer

How Did the Build Reach Passive House Standards?

Features include:

Texas Passive House Wall Assembly
Texas Passive House Wall Assembly. Photo Credit: Trey Farmer via House So Green

How Do Passive House Guidelines Apply In Texas?

Passive House standards focus on energy use. "You add more insulation; windows are typically better than code. We have triple pane, and the code here is double pane," Trey says. "The big lift here is airtightness. This is the thing about passive house that is the most foreign in our market because it's not something we really have to think about here."

Because of Austin's climate zone, the codes for airtightness are low — five air changes per hour. "It's three changes in other parts of Texas and the rest of the country. In a Passive House, it's 0.6. Once you get down to 2 or 1, you get pretty big energy savings because you're not leaking air that's been heated or cooled."

At that level, you also don't have any dust, pollutants, or allergens coming in through nooks and crannies. "You get a big indoor air quality benefit."

The ERV continuously runs to bring in the fresh air that's filtered and tempered, so the Farmers aren't paying the energy penalty from Austin's typically hot, humid air. They also have a dedicated dehumidifier, which Trey says he specifies for all his Austin projects.

Passive House guidelines offer targets for heating and cooling demands during peak conditions and total annual demands. The targets vary based on the project type, size, and location. You model your house in 3D and arrange it on the site, including all of your window parameters, wall and roof assemblies, HVAC system, and appliances. That model tells you an assumption of how much energy your house will use and if you're meeting those targets.

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At our neighbor's house, which was identical to ours [before the Passive House retrofit], it was 36°F. They may as well have been living in a tent.

Outdoor temperatures would be below freezing for a record 144 hours. The Farmers' house warmed up slightly during the day because of south-facing windows, but on the second night, it got down to 53°F inside. The following day the family went to stay with friends who still had power. "A neighbor checked on our place," Trey says. 

The coldest our house got was 49 degrees on the third day. It was quite a bit warmer than many people's experiences.

Proof of Concept

A February 2020 Rocky Mountain Institute study, "Hours of Safety in Cold Weather: Framework for Considering Resilience in Building Envelope Design and Construction," looked at how long a home could maintain thresholds of comfort and safety before reaching unsafe indoor temperature levels. It found that "homes with Passive House standard building envelopes and net-zero energy buildings maintained safe indoor temperatures for significantly longer than even code-compliant new buildings, lasting over six days before indoor temperatures fell below 40°F."

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Trey believes that overall, his house "performed well. It was a good case study and proof of concept from a passive survivability standpoint."

Here's the crew that helped create the Farmers' house:

Contractor – CleanTag LLC

Structural Engineer – Lester Germanio

Mechanical Design – Positive Energy

Mechanical Installation – New Results

Landscape – Austin Outdoor Design

Article By

Stacey Freed

I’m constantly on the hunt for a way to hike and write simultaneously.