Just over two years ago, Colorado’s Marshall fire swept through the town of Louisville, where Alpen is headquartered. It destroyed 1,084 homes and damaged hundreds of other structures, displacing thousands of Louisville residents. Now, those who were most affected by the fire are faced with difficult decisions as they rebuild their homes and lives. Some homeowners have recognized Passive House principles as a solution for creating resilient, fire-resistant homes.
Our team recently toured the Marshall Fire Zone and were interested to see several Passive Homes under construction. As an industry leader in energy-efficient windows and doors, (which are integral components of Passive Houses,) we are excited to delve into the role Passive House building principles play in fire-resistance.
Streamlined Design Protects from Firebrands
Photo of Firebrands courtesy of Fire Safety Research Institute
At the core of Passive House design is a simplified form factor, strategically reducing thermal losses from exposed surfaces. Beyond energy efficiency, this design mitigates the risk posed by firebrands – flaming or glowing particles that can readily ignite debris or cladding during a fire. By eliminating complex exterior geometries, Passive Houses effectively prevent firebrands from finding vulnerable spots around the structure.
Robust Windows for Heat Stress Mitigation
In Passive Houses, Triple-pane windows in substantial frames play a crucial role in reducing vulnerability during a fire. The use of tempered glass and over-insulation adds an extra layer of protection, significantly delaying the potential failure of windows due to heat stress. This not only enhances fire resilience but also contributes to the overall durability of the home.
Focus on Fire-Resilient Materials
In the aftermath of the Marshall fire, it is evident that the choice of building materials makes a big difference. Passive House builders prioritize fire-resilient materials for claddings, decks, fences, roofing, and insulation. This goes beyond eliminating foam insulations, emphasizing environmentally friendly alternatives like dense-pack cellulose or mineral wool. These materials not only resist flame spread but also contribute to creating healthier indoor environments.
Insulation Strategies
Fully insulating assemblies, including service cavities, is a key Passive House strategy that enhances R-values and minimizes the possibility of flames spreading within the structure. This approach is particularly valuable in roofs, where appropriate insulation, elimination of vents, and full coverage of framing create limited access points for fire ingress.
Incorporating continuous exterior insulation layers, such as mineral wood board or fire-rated wood fiber board, further fortifies the fire resilience of cladding and roofing. Adding a rainscreen and creating a vapor-open assembly are additional measures that contribute to a more robust structure.
While not certified Passive, Colorado Earth Home (Left) is being constructed from Stabilized Earth Bricks and is being built to be fire resistant using similar insulation strategies.
Surviving Smoke Exposure
Passive Houses not only resist fire but also excel in managing smoke exposure. During the Marshall Fire, a Passive House retrofit owned by builder Mark Attard withstood the fire front with minimal smoke damage compared to neighboring homes. This underscores the idea that Passive Houses not only provide fire resistance but also ensure a healthier indoor environment during wildfire events.
In conclusion, while the concept of Passive Houses is synonymous with energy efficiency, their application in creating fire-resistant homes is becoming increasingly apparent.
As we continue to reflect on the lessons learned from the Marshall fire, it is clear that the integration of Passive House principles can pave the way for homes that not only meet high energy performance standards but also stand resilient in the face of unforeseen challenges.
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