Most people would assume it makes zero sense to build a passive house in a hot, humid climate. The indoor/outdoor temperate differences aren’t as extreme as they tend to be in other climate zones.

But a passive house still offers a huge performance increase from traditional building methods, and a great improvement in the indoor air quality – a major attraction to homeowners. Not to mention the reduction in energy bills. In a cold climate, a passive house is projected to reduce energy expenses by 90%. In a hot climate, more like 70%*.  Still a signifiant savings, and worth the investment in additional time and materials up front.

Choosing Investment vs. Expense

From the financial side, the theory is that you’re spending more money on performance, then that money gets divided over the life of your mortgage. If you can spend $30 more a month on a mortgage, while achieving $100 savings a month in utilities – you’re at a major advantage.

Not only does it make a lot of sense, it’s something energy efficient builder Mark Larson, CPHC, Built Green Texas, can readily convey to his clients as a professional builder and consultant. 

“When you allocate your money this way, you’re choosing to invest in the value of your home, not the expense of living in it.“

-Mark Larson, CPHC, builder, Built Green Custom Homes, Austin, Texas, and homeowner

Performance Metrics Make the Difference

Mark Larson started his career in corporate real estate. He decided to make the leap into building because he loved that side of the business. If he was going to completely change careers and build houses, he wanted them to be the best ones on the market.

That’s how he discovered passive house design. It’s the most stringent building metric in the world, but also the only one that is performance based. It’s not prescriptive like LEED, meaning certified to operate a certain way in theory. Passive houses MUST perform as they are designed, or they don’t achieve passive house certification. They have to hit certain metrics for air tightness, measured with a “blower door test”.  The fact that the performance is completely measurable was much of the appeal.

“I’m a huge fan of performance based metrics – which is exactly what passive house offers. I knew my family would live and breathe in the highest indoor air quality. It really matters.”

-Mark Larson, CPHC, builder, Built Green Custom Homes, Austin, Texas, and homeowner

Blower Door Testing

IAQ Texas conducted the initial blower door testing. But Mark didn’t get the results he was hoping

for, so he employed his own blower door contraption to help find leaks. Mark used a 2500 cfm construction ventilation fan and taped roof underlayment around the door opening.

He found some opportunities for better air sealing between the top plates, and at plate boards butted together. The attic hatch was also a source of leaks. Zip tape was sealed into a 90 degree corner, but air leaked out the ends of the length of tape. Some random nail holes and a few casements windows needed slight adjustments to better seal when closed.

Once those changes were made, Mark’s passive house rater from ATS Engineering did another blower door test before adding interior insulation. These results surpassed Mark’s expectations, and made it below the Passive House metric of .6ACH, and hit .57ACH. (via instagram, Feb 1, 2019). This figure is expected to drop even lower once interior insulation and drywall are added.

The Building Envelope

Mark spent a significant amount of time researching the materials he wanted to use for his home. For the building envelope, he used 2″ x 6″ studs, 16″ on center, Zip sheathing, Rockwool ComfortBoard exterior insulation, and Alpen windows. He had discovered ThermalBuck years prior, and was excited about finally having the chance to use it on his own home.

“ThermalBuck simplifies the water, air, and thermal control layers of window and door installation. It solves a specific problem of how and were to flash windows within continuous insulation. ThermalBuck will always be a tool in my design toolbox to solve the complexities of “outies” in CI,” said Larson. 

“It solves a specific problem of how and were to flash windows within continuous insulation.”

-Mark Larson, CPHC, builder, Built Green Custom Homes, Austin, Texas, and homeowner

Passive House Austin

Mark is part of a dedicated group of building industry professionals working to make passive design well-known in the Texas market. Passive House Austin promotes the principles of passive design through events, podcasts, workshops, and most notably, the Humid Climate Conference. Held annually in Austin, the Humid Climate Conference recently featured Joe Lstiburek, widely recognized as the leading building science expert in the industry. It draws building professionals from all over the South, to focus on issues specifically related to their climate – offering a huge benefit over national or international events.

To learn more about Passive House Austin, and view more photos from the recent Huber sponsored happy-hour event at Mark Larson’s passive house build with IAQ Texas and Positive Energy, click here.

Helpful Links & More Info:

Mark Larson Instagram
Built Green Custom Homes, Austin Texas
Passive House Alliance – US

* homebuilder estimates from personal research