Rebuilding Fire Resilient Passive Houses in Colorado

Homeowners in the U.S. can build and improve their homes to be more resilient to increasing climate extremes. We aim to educate homeowners about climate-related risks and opportunities to reduce potential damage to homes and save lives. 

 

In this series of Stories, we share examples of homes built to withstand local climate risks. This blog focuses on a project designed to be a safe home for wildfire victims. 

 

The RESTORE Passive House is a predesigned passive house aimed to replace homes destroyed in the Marshal Fire in Colorado in December 2022, which burned an estimated 1084 structures, and another 149 were damaged.

The team completed the design process, and the city of Boulder granted the permit for the first projects. The construction of two homes began on February 2023 in Boulder County, CO.  

Andrew Michler, a passive house designer, acts as the passive house consultant and champion for these projects and helps design and develop an awareness of the passive house concepts and benefits. Michler cooperated with Joubert Builders, and Harrison Architects, an architect firm experienced in passive house construction, and led the consultant for the first certified passive house in Seattle. 

 

Climate Risks

The RESTORE passive house Colorado was designed primarily to address the climate risk of wildfires, smoke, and extreme temperatures for prolonged periods.

In recent years Boulder is experiencing more extreme temperatures and weather events, including a significant increase in the number of high-temperature summer days. A temperature above 90 degrees Fahrenheit is not uncommon anymore, even in the fall season.

 

In addition, the air quality in the region has decreased. Cooling houses by opening windows is no longer optimal due to smoke from wildfires, and other airborne conditions, such as the ozone. The ozone in the Denver metropolitan area in Boulder was downgraded from “serious” to “severe.” The ozone levels in the area are higher than EPA’s air quality standard, which can cause breathing-related issues such as bronchitis, emphysema, asthma, and skin and eye damage.  

The Marshall Fire in Colorado was a collective wake-up call to wildfire risk within urban and suburban surroundings. While it occurred outside the Boulder City limits, it was the most destructive in Colorado history. The Marshall Fire happened mid-winter, which illustrates that there is no such thing as a fire “season” anymore. 

Wildfires also pose a risk of smoke damage even to distant homes. The Marshall Fire Colorado caused severe smoke damage to many houses and prevented occupants from returning to their homes though their houses were not destroyed. 

Climate Resilience Strategies
 

Passive House is well known for its extraordinary energy efficiency, which increases the home’s climate resilience. It is designed to maintain comfortable climate conditions for occupants without a significant need for heating or cooling. In power outages, a passive house can maintain livable temperatures for up to 36 hours, despite extreme temperatures outside. The main components that allow it are the airtightness of the house’s envelope and the thick and continuous insulation in the walls. 

Passive houses are naturally more resilient to wildfires due to several characteristics based on the basic principles of the Passive House. Note that the strategies are fire resilient only if put together in a proper assembly.

The following are specific climate-resilient strategies specified in the Passive RESTORE House Design:

• Densely packed cellulose insulation treated for fire. All the air is pushed out, preventing air from entering the wall system, which makes it much less flammable.
   
• Two inches mineral wool exterior insulation system.
   
• An airtight membrane named Intello helps seal the envelope while allowing moisture out of the wall cavity to avoid excess build-up. The membrane controls air while operating as a valve to help buildings dry. Other similar membranes required by code don’t allow vapor moisture through, which can lead to moisture build-ups and mold.
  
  
   
• Passive House Institute (PHI) -Certified Energy Recovery Ventilation (ERV) unit called Brink distributed by 475 High Performance Building Supply. One fan brings fresh air into the house and distributes it in the living space. Another fan takes the air out of the house, usually from more contaminant-risk areas, such as the bathroom or kitchen. The air flows through a membrane that can recover energy when the air is replaced. This way, the house gets a complete air change every two or three hours. A Passive House always incorporates a fresh air system in an airtight building that controls the amount of air infiltration to the building and can be enhanced by additional air filters.
   
• Simplified Form Factor: The structure’s design is simplified, originally, to preserve heat. A simple design reduces the area exposed to exterior temperature, which decreases heat loss. This strategy also protects from wildfires as the simple design eliminates nooks and crannies where embers usually accumulate, thus is less susceptible for firebrands to lodge into the home’s fabric and ignite. Michler thoroughly explains this concept in a video that walks us through his own certified passive house.
   
• Metal roofs are less susceptible to wildfires and don’t ignite as easily as timber roof systems. The roof is considered the most vulnerable element of the house to flames, so it’s crucial choosing a fire-resistant roof. Choosing fire-resistant building materials wherever possible in a high fire-risk location can save lives and reduce damage.
   
• Vents are eliminated within the house’s structure to prevent embers from entering the house. Although most codes require ventilating the roof to allow air penetration and avoid moisture and mold buildup, it is one of the primary ways for buildings to burn down during fire events. Even with fire-retardant vents, a significant amount of hot air can enter the roof system through them. Instead, this passive house has unvented closed-roof systems. The insulation continues to the roof deck, preventing airflow. The Intello membranes installed under the roof system help dry the roof without airflow.
   
• Fiber cement or cement board sidings that are fire-resistant.
   
• Triple pane windows by Alpen with tempered glass prevent heat from the fire to break the glass and prevent the embers from entering the house and burning the house from the inside. The tempered glass increases energy efficiency and makes the glass stronger and much more fire-resilient.
  
  
  
   
• Energy-efficient mini split heat pumps are used for heating and cooling, distributed by Small Planet Supply.
   
• Landscape: about four feet of hardscape around the house to eliminate flammable objects close to the structure. The decks and plants are fire resilient to help wildfire mitigation.

 

Building Codes in Colorado

Michler believes the International Building Codes (IBC) are strong enough to ensure structures withstand snowstorms in Colorado. The code is also strong enough to mitigate damage by windstorms or extreme element conditions. Yet the code fails to include maintaining habitable conditions in incidents of power outages or low air quality. Both are crucial emerging aspects of resilience and should be considered by builders and designers before starting construction. 

The city of Superior adopted the 2021 International Energy Conservation Code (IECC). Despite significant code improvement in the past decade in terms of energy-efficient design, the Passive House is more energy efficient than the latest energy codes. Michler believes that is where the energy code will end up eventually, where buildings use 80% less energy than today.

As the Passive House consultant for the project, Michler is working with the city of Superior to encourage Passive House as a compliance path for the energy code by conveying how Passive House is significantly more stringent than the most updated building codes adopted. 

 

Cost

The cost of rebuilding has been a primary issue in this project. In addition to the extraordinary cost increase of building in the U.S., Boulder is one of the more expensive areas in the country to rebuild. Aside from the personal devastation of destroyed homes, there is a lot of confusion about coverage of the damage from insurance companies. Most homeowners were underinsured for replacement costs. There is an existential question of whether insurance companies will continue to offer insurance for reconstructed homes and how insurance companies will adapt to a new setting where buildings are more susceptible to climate conditions.

Xcel Energy, the primary utility service provider for energy for natural gas and electricity, has provided a substantial rebate of $37,500 for rebuilding certified Passive Houses, which was a significant motivator for the project. This significant rebate largely contributed to the conversation around the project.

In addition, the State of Colorado offers an additional $10,000 rebate for all-electric homes. Combining the two, close to $50,000 rebates allow offering homeowners the project. 

There has been an effort to lower the cost of construction as much as possible. The team manages to reduce the cost to about $550,000 for a basic two-story with a full-size basement and approximately 2,500 square feet of living area. This cost is roughly in line with or less than the cost of Energy Star Homes, yet more expensive than building a basic 2018 code house with very few extra frills.

 

Andrew Michler

Andrew Michler is a designer and Principal of Hyperlocal Workshop, a Passive House design group based in Colorado with a mission to design structures that will adequately function for decades. He built and resides in the first certified Passive House in Colorado. Since the house is located in the woods, a significant amount of work was done on fire resilience.

Michler’s family lost their house in the Oakland Fire in 1991. Rebuilding the house with his father was the beginning of his career. Michler has always been sensitive and appreciative of the climate and our planet. Realizing the negative impact of buildings on the environment, he diverted his interest and work early on to sustainable homes. After purchasing an off-grid cabin in the mid-90s, he engaged in learning about energy efficiency and energy systems but struggled with scattered, undocumented, and unmeasured information.

After multiple unsatisfactory projects with different approaches, including LEED and similar third-party voluntary certification, Passive House’s physics-based quantifiable process resonated with Michler and transformed his approach to looking at buildings. 

Michler is a hands-on professional who makes sure to experience firsthand how elements work by testing conditions in his own passive house and engaging in the installation of different components. Only after installing the insulation several times and thoroughly understanding how to apply the product within thicker wall systems, and only after feeling comfortable with the procedure, he started specifying it in his projects. Michler also purchased and installed sample heat pumps in projects and his home to understand the installation process, their effectiveness, comfort, and ease of use.

His house proved smoke damage resilience in Cameron Peak Fire in October 2020, which burned 220,000 acres and destroyed 469 structures in Colorado.  The flames reached the edge of his property, and smoke blanketed the house for at least a couple of weeks, but the airtightness component maintained the interior air quality. The same occurred to a retrofitted passive house owner in Boulder County. The wildfire stopped across the street, so the home survived the fire. But that homeowner was the only one to return home while all other evacuees stayed away for months afterward due to the substantial smoke damage.

 

 

Alongside demanding design and consulting commitments, Michler continuously shares his climate-resilient design education and experience in various forms:

• The organizer of the Passive House Rocky Mountains (PHRM), an advocacy and educational organization that partnered with the passive house network after its development. The PHRM developed a culture around Passive House and brought many educational resources to the public, including continuing education for professionals.
• Author of the book “Hyperlocalization of Architecture” on contemporary sustainable architectural archetypes. The book captures concepts such as resilience, zero carbon, and regenerative design.
• Promoter and champion of the Passive House concepts wherever possible, including motivating the project’s builder, Chuck Bower, to take passive house builders training.

 

Overcoming Challenges

Numerous challenges typically emerge in the design and construction processes and have the potential to amplify when it comes to building climate resilience. Examples are budget, communication among the different service providers and the customers, and lack of understanding of climate adaptation strategies. 

 

Predesign

Generally, a passive house is designed individually according to the specific project’s conditions. This project is unique as it was predesigned and precertified before approaching potential homeowners. Having gone through the traumatic damage from the wildfire, homeowners wished to build a fire-resilient home, be involved, and understand the costs, the visual aspect, the concepts, and the resilience of a passive house. All this information was necessary for homeowners before adopting this design. It was a new process for the building professionals involved and for PHI and included much thought.
This process involved informative meetings where all service providers submitted their insights on the design. The inputs and guidance from all professionals, including the builders, engineers, designers, and contractors, were crucial to understanding the potential challenges, complexity, and feasibility of the construction process and the estimated labor cost.
The effort resulted in a design that can be replicated throughout the City of Superior and Boulder County. Michler leads two additional RESTORE projects.

 

Rebuilding for fire victims

It is always tough to rebuild for someone who lost their home. Each victim has a complicated personal story and different opinions on how and what to rebuild. 

Rebuilding a house after a fire typically takes an extensive amount of time in which homeowners consolidate their finances and debris is cleared out, along with other complications, such as pulling permits and design processes. 

Although it is a delicate situation, it’s essential to educate homeowners why a passive house is a better option than regular construction or even an Energy Star house. This effort results in initiating a conversation with potential homeowners to adopt this concept and design. At least a dozen home rebuilds in the Marshall Fire area will be passive house certified.

 

Choosing building materials

The choice to construct a wooden house was an attempt to avoid using materials that might exacerbate climate change. Concrete, for example, is considered durable and strong, but has an extremely high carbon-intensive production process. Foams used for insulation are made of petroleum and use high global warming potential gasses. Michler tries to avoid those materials as much as possible in construction. Instead, he implements two-by-eight timber construction and specifies cellulose for insulation and materials that are bio-based but still fire-resilient when properly assembled. 

The PHI certifies components tested according to uniform criteria and of excellent quality regarding energy efficiency. The certification facilitates the material selection but still leaves the challenge of cost and availability. Cellulose insulation, for example, is needed in large amounts in a passive house. The team invested significant time and effort to ensure the insulation was purchased at an affordable cost, locally made, and available. Although the team planned to use PHI-certified prefabricated panels, the project’s scale was too small to buy those panels. The challenge is finding the match between the quality and availability of a product, its climate impact, its ease of use, and its cost efficiency. 

Still, the most crucial aspect is that builders/designers have previous experience with the installation because the best material in the market will not function as desired if it isn’t properly installed. 

Hyperlocal Workshop uses the passive house concepts as a design baseline for the building’s functionality and is creative with applying the architecture and materials as long as the components work together. Current examples are a straw panel building and cabins constructed of mass timber using wooden nails.

 

Final Thoughts
 

Designing with climate risks in mind may be more complicated than regular construction since new multiple factors go into the equation, yet, it’s feasible. 

 

Adapting to climate change and future extreme events can be done by acquiring existing education and information, factoring in all aspects at the beginning of the design, and making sure the goals are clear and communicable. 

 

The Passive House concepts support the construction of highly energy-efficient homes that can provide comfortable conditions despite extreme outdoor temperatures or power failures. Those concepts also protect from flames and smoke due to wildfires and contribute to the climate resilience of the passive structures.

 

Andrew Michler believes “it is the future of buildings, and we don't need complicated, and expensive systems to create such conditions.” 

Michler promotes the passive house concepts for years but recently has taken on the delicate and complicated task of rebuilding homes for fire victims, which requires a gentle approach with homeowners after trauma while maintaining a firm dedication to the concepts he believes in. 

 

It is possible by carefully selecting the building materials as part of his design, making sure they are available and affordable and can be installed relatively easily, and educating fellow professionals and homeowners.

 

Michler walks the walk, lives as he preaches, and implements climate-resilient strategies firsthand before recommending them to others. Professionals like Michler are paving the way for others to achieve energy-efficient, safe, and climate-resilient homes. 

Michler admits it is an ongoing learning process with contradicting information, new technologies, and emerging products that should be tested in theory and practice.

 

eampact strives to help with providing information on climate risks and solutions, vetting building products that are climate resilient and eco-friendly, and professionals experienced in implementing climate-resilient strategies. We are excited about the growing community around properly building homes for people, nature, and the climate.