101 Series: No Thermal Bridges (WED 12/6, 9am PT/ 12pm ET)
March 17, 2023

Real-World Benefits of a Passive House Retrofit

Real-World Benefits of a Passive House Retrofit

It has been a little over a year since my community, Louisville, suffered one of the worst natural disasters in Colorado history. The Marshall Fire ripped through our neighborhoods in December of 2021, destroying more than 1,000 homes while simultaneously impacting people's sense of place and safety. Some of those who lost their homes will never return. They simply can’t afford to rebuild or in some cases would rather not return to live in a place that reminds them of such painful memories. 

Sometimes what is overlooked in the conversation of lost homes and the need to rebuild in a more resilient way is the fact that many homeowners who didn’t lose their homes suffered extensive smoke and heat damage. Even months after the fires, some of those homeowners have yet to return to their homes, as they are still dealing with smoke, soot, and ash. 

My family and I are ever thankful that we did not have to endure either experience. While we were very lucky that our house didn’t burn, we can attribute the fact that we were able to move back into our home within a couple of days to us having undertaken a Passive House retrofit. 

Several years before the fires, we had started to retrofit our home using Passive House methodology. In fact, in the fall of 2021 we had made one of our final improvements and switched off the gas to our house when we installed a heat pump for heating and cooling. This small act ended up helping us to return to our home within a couple of days after the fires. As it turns out, when there is a fire all the utilities are shut off so as not to contribute to the fire’s spread and for the safety of the first responders. The first utility to return, typically within one day of a fire, is electrical. This allowed us to return to a warm home. Others, unfortunately, could not because their homes were heated with gas. 

In addition to our good fortune of having gone all electric, the fact that our home was well air sealed and had filtered mechanical fresh air paved the way for us to return to a home that had healthy indoor air quality and no smoke damage. Unlike our neighbors, when we returned the day after the fires we walked into a home with no smell of smoke and only a small trace of ash. Testing proved that the pH, chemical, and soot levels in the house were normal, and no further action was required. After the electricity was restored, we turned on the heat pump and the ERV and have lived in our home ever since. As the fires continued to smolder and the outdoor air quality continued to be toxic, we were able to live in our home without worry of becoming sick or potentially experiencing the long-term effects of breathing air heavy with melted plastics, metals, and other chemicals. Without the steps that we took to retrofit our home, we could have faced months of restoration work such as insulation remediation, not to mention window, drywall, furniture, and clothing replacement. It can't be overstated how important it was that we were able to return to our home, our lives, and our normal routines with minimal disruption. 

In our practice we often speak with clients about indoor air quality as an important benefit of Passive House construction. It isn't often, though, that we are able to point beyond charts and scientific jargon to real-world examples of how indoor air quality can impact lives on a daily basis, not to mention when there is a toxic event such as an urban wildfire. The ash and char produced by an urban wildfire can contain heavy metal, dioxins, and furans. The air can be heavy with carbon monoxide and volatile organic compounds (VOCs) such as benzene, formaldehyde, and a wide variety of polycyclic aromatic hydrocarbons (PAHs) such as pyrene, phenanthrene, and particulate matter. Exposure to such poor air quality can result in reduced lung capacity, chronic illnesses, pulmonary and cardiac disease, and cancers. Clearly, when a home is built without taking into account air tightness and filtered mechanical fresh air, then the impact of a wildfire is much greater than in one built with these standards in mind. 

The good news is that we know how to avoid many of these tragedies—with a good air sealing strategy and mechanical fresh air. The homes in my neighborhood were built in the late 1980s and early 1990s. At the time, the building world was unconcerned with air sealing and indoor air quality. Building science was not yet part of most builders’ vocabularies. For most developers and builders, the idea was to build as quickly as you could sell. Homes were not viewed through the lens of quality, durability, and resilience. 


It is fair to assume that, because my home is part of a production home development, all the homes in my neighborhood were built to the same poor quality as my house was—before it had been renovated—and, unfortunately, none of the others had been retrofitted at the time of the fires. With winds gusting to 85 mph and flames moving at a 1,000 feet per second, it is no wonder that these homes suffered the damage that they did. 

Before starting my retrofit, I decided to establish a baseline by which I could measure my improvements, and then I developed a plan that I could implement over time. While I knew my house was uncomfortable, it was shocking to me how far from even code it was. The baseline blower door test was 17 ACH50! On a 45°F day, the interior temperature of one of my window’s center of glass was 50°F and the aluminum frames were even colder. My opaque wall surfaces were 59°F. 

When implementing my retrofit plan, I started with the low-hanging fruit first and made over the crawl space area by adding insulation to the floors and walls and installing a 15-mil vapor barrier over the floor and mechanically fastening it to the foundation. I then addressed air leakage between the foundation and timber-framed portion of the house. Because the siding on my house was failing and in need of replacement, I took the opportunity to replace the windows, air sealing them to my newly installed water-resistant and air barrier before adding 5 inches of continuous mineral wool insulation. One of the final pieces was to add a filtered mechanical fresh air system to the home. To do this, I needed to convert the attic to conditioned space allowing for the placement of the ERV and ducting. We used a Broan ERV and added an inline filter box to allow for MERV-13 and charcoal filter placement on the intake side of the unit. The last piece was the addition of a heat pump for heating and cooling, which eliminated all gas-fired appliances from the home.


All images courtesy of Mark Attard

Outside of the Passive House world, the trend of electrification can be misguided. On the surface, electrification would seem to fit well with the general movement towards a more sustainable housing stock. The problem, particularly for existing homes, is that there is very little discussion of how to upgrade the efficiency and the comfort of these homes in a way that would create real resiliency in the face of current and future climate disasters, leaving us in much the same position we are currently in. As just one example, many strategies for electrification rely on limited resources (lithium, silica) without a plan for managing those commodities for our long-term use. While this switch ostensibly moves us away from fossil fuels as our primary energy source, it still leaves us with a building stock that is vulnerable to natural disasters and does nothing to address the comfort and health of the occupants, the results of which we experienced in the Marshall Fire. While a thousand homes were lost, the totality of the disaster was exponentially increased due to poorly built homes that were left standing. 

Ironically, the far less glamorous option of retrofitting through air sealing a home offers one of the greatest benefits to our existing building stock because it decreases energy loss, increases comfort and durability, and allows for better control of IAQ. Moreover, this can be one of the least expensive ways to improve building performance. 

While it is important that the homes we build and retrofit for our clients maintain the highest levels of comfort and health, one of the basic benefits of sustainability and resilience is the ability to shelter in place during and in the aftermath of catastrophic events. In our tiny neighborhood of 20 houses there were countless lost work hours, and extraordinary financial losses, not to mention the emotional and psychological tolls on my neighbors. Multiplying that across thousands of households is unfathomable, but this is the reality we face. As we continue to fall deeper into the climate crisis, these events are happening multiple times on an annual basis. 

As municipalities across the country look to adopt carbon neutrality goals, the issue of how to address our existing building stock becomes ever more important. With 40% of the global emissions coming from buildings, they cannot be ignored if we want to meet any climate goals. Improving and maintaining our building stock is a greater act of sustainability than trying to replace it with new construction, even if it is high-performance. 

Certainly, education is a key component in achieving sustainability goals, but developing air sealing and indoor air quality programs to pair with incentives to electrify our homes and amending our building codes would help increase the speed at which we can turn our existing building stock into efficient, comfortable, and durable assets instead of the existing liabilities that they are. As we learned when doing our own retrofit, the easiest upgrades, like air sealing and adding filtered, mechanical fresh air, offered the greatest benefits. Depending upon the home, these improvements can be accomplished for around $10,000.  More importantly, these kinds of retrofits will increase our community resiliency and bring peace of mind to the building owners that may not have to face months of repairs and the emotional losses from having to be displaced from their homes when facing down a climate disaster. 

Mark Attard

Mark Attard

Mark Attard is the Operations Manager for Hammerwell, Inc., a Passive House custom home builder in Boulder, CO.. They are currently rebuildi...

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