Damage from the Marshall Fire in Boulder County on Dec. 30. Credit: Anthony Albidrez.

After Andrew Michler lost his home during the 1991 Oakland Hills Fire, he took the rebuilding process into his own hands. Today, he works as a certified “passive house” consultant and principal of the design firm Hyperlocal Workshop, helping people build ultra-low energy homes that reduce climate-warming gasses and better withstand an extreme weather disaster. 

Having designed and built Colorado’s first passive house in 2020 — a virtually airtight building that uses very little energy for heating and cooling — Michler made his expertise available to Marshall Fire victims during a March 3 webinar on the feasibility of rebuilding net zero after the disaster. The goal of the nearly two-hour presentation, hosted by the Boulder County chapter of the Colorado Renewable Energy Society (CRES), was to equip homeowners with knowledge and advice to rebuild their destroyed homes with a focus on climate resilience. 

Last week, the Louisville City Council moved to exempt Marshall Fire victims from the 2021 update to its building code. The decision followed a lengthy public comment session during which many victims expressed their anxiety and uncertainty over the additional cost of rebuilding to the most recent code, which adopted the 2021 International Energy Conservation Code (IECC) standard along with additional requirements. Some victims said they planned to build to the 2021 standard whether or not the exemption passed. Others said that they would build to the highest standard their budget would allow.

Michler discussed the benefits and logistics of building to the International Passive House Standard (much higher than the IECC code), the outsized effect of buildings on global carbon emissions, Xcel Energy incentives for Marshall Fire victims and more.   

Firewise home: ‘Think like a log, not like a bundle of sticks’

Designing fire-resilient or “firewise” homes was the first topic covered by Michler. 

He began with a metaphor: “If you ever tried to make a campfire, you always want to start with a lot of sticks — you don’t want to start with a big log.” The bundle of sticks will burn more easily than the log because there are more air pockets and a greater surface area. Likewise, a house with a simpler design that minimizes external surface area is harder to burn than an ornate house with many complex elements. Michler urges builders to “think like a log, not like a bundle of sticks.”

Michler discussed how building codes can make houses less susceptible to damage or destruction by wildfires. The airtight design of a passive house keeps out smoke and embers. Other ways to make one’s house more firewise include insulating the attic to keep embers from coming in an outside vent, using tempered glass for windows and replacing typical insulation materials like foam and fiberglass with less flammable materials like mineral wool. 

Michler summed up this philosophy as “build tight and ventilate it right.”

Housing and carbon: Passive houses eliminate use of fossil fuels

Buildings and construction make up 39% of global carbon emissions, according to a 2019 report from the Global Alliance for Buildings and Construction. Manufacturing building materials such as aluminum, steel, and cement account for over 11%. This, Michler said, is why building an energy efficient home is so important.

On the energy side, many passive houses eliminate use of fossil fuels onsite, meaning no natural gas lines and a roof that is ready for solar energy. They also use all electric equipment for heating, cooling, hot water and cooking. Michler said an air source heat pump is likely to be the most cost-effective, low-carbon heating method.

In addition to energy consumption, Michler said 40% of a building’s carbon footprint over its lifetime is from the materials used to build the house. Concrete is the largest source of carbon dioxide among building materials, so using alternatives is vital. Mainstream low-carbon alternatives include cellulose or wool for insulation, along with light wood framing and hempcrete, which is carbon negative.

Xcel Energy incentives: Unraveling the confusion

Xcel Energy is offering Marshall Fire victims rebates to rebuild their homes to energy efficiency standards. “Almost globally, this is unprecedented … to my knowledge at least,” Michler said. He said a Canadian utility had executed a similar program, but that he had not seen it in the U.S. 

The incentives include $37,500 for constructing a passive house, with lower payment amounts for lower efficiency standards, such as $17,500 for a house that meets the Energy Star certification standard. A passive house, according to Xcel, will see 60% to 80% lower heating and cooling costs compared to a house built to the minimum code.

Xcel is also offering a $7,500 rebate for meeting only the 2021 IECC code.

Michler addressed confusion over how much rebuilding to energy efficient standards will cost. “To be honest, when people are throwing out these numbers about what green building costs, a lot of them are literally making things up or are throwing out numbers that are hard to quantify,” Michler said.

Would the $7,500 rebate cover IECC costs?

In an email to the Boulder Reporting Lab, Christine Brinker, senior buildings policy manager at Southwest Energy Efficiency Project (SWEEP), also expressed frustration about “ridiculous estimates” of the cost to rebuild efficiently. She said the cost estimate done by Pacific Northwest National Lab (PNNL), which was presented at the Louisville City Council meeting, is the most reliable. PNNL estimated the additional cost of meeting only the 2021 IECC code to be $4,789.

Asked about Xcel’s incentive for Marshall Fire victims who voluntarily rebuild to the 2021 IECC standard, Brinker said the $7,500 rebate “would more than cover the expected cost increase of going from the 2018 IECC to an unamended version of the 2021 IECC, for an average house.” 

She added that the $7,500 would cover most or all of the cost of building to Superior’s or Louisville’s most recent building codes, except for Louisville’s net zero appendix, which requires houses produce all the energy they use on-site through solar panels or buy it through a solar garden subscription. 

“That is the wildcard, because there are so many different ways to reach it. Meeting the appendix requires increasing the efficiency and meeting the rest with solar. SunShare has already promised solar for affected homeowners at no additional cost than what they’d already be paying Xcel, so we can zero out that cost.”

Mariana Pickering, the co-founder and CEO of the passive house consulting firm Emu Systems, offered advice to anyone interested in building a passive house: Find an experienced passive house builder.

“Generally speaking, the percentage increase [in cost] also goes down with the experience of the builder,” she said. “Their first [passive house] build is a steeper learning curve, but once they have done it, it becomes part of their workflow.”

Despite having a higher price tag than a conventional home, passive houses have other benefits besides energy savings, according to Pickering. “The biggest actual cost differences homeowners will see is in window packages, but that is also what results in the highest yield for non-market costs like health and safety,” she said. “The biggest value is the indoor environmental quality that is created for the occupant.”