You’d never guess this new two-story, three-bedroom home just outside Gig Harbor, Wash., is a milestone in sustainable residential construction.
The 1,500-square-foot home is Habitat for Humanity’s first zero-carbon home. “The home is built with concrete that uses a sand replacement made of a biosolids waste product called biochar,” explains project architect Cameron Walker of Tacoma, Wash.-based Ferguson Architecture.
“This form of biochar sequesters carbon without diminishing concrete durability and energy performance,” Walker says. “It transforms a waste product nobody wants into an effective building material that locks up carbon for thousands of years. It’s a practical, emerging environmental solution.”
This sustainability breakthrough is the central component of a building system called insulated concrete forms (ICFs). ICF is an affordable construction method that uses Lego-like foam blocks to form a cast-in-place, steel-reinforced concrete wall system.
“It was our first ICF project,” reports Habitat for Humanity’s Jonah Kinchy, the local affiliate’s director of site development and construction. “Even though it was new to us, the documentation and instructions made every construction phase surprisingly easy.” Carbon neutrality and constructability weren’t the only things that surprised Kinchy and Walker. Here are a few highlights:
• Design Flexibility. Walker credits superb documentation from project partners and overall system simplicity for his smooth transition to ICF. “Even though it was unfamiliar initially, I felt really confident about moving forward,” he says. “The system worked really well with our original design intent.”
• Energy Conservation. Kinchy says the inherent air sealing properties of ICF along with building mass allowed them to moderately downsize the HVAC system. “We barely did any air sealing other than the attic space. My guess is the HVAC unit won’t run much. The structure will hold a steady, comfortable temperature all year round.”
• Code Compliance. In recent weeks, the state’s new mechanical, envelope, and lighting requirements went into effect for all new construction. Walker says the changes the code mandates, such as continuous insulation, have become a “… super-hot topic right now. There are a lot of conversations about the best ways to meet the new water barrier, insulation and durability requirements. ICF solves it all. It automatically complies with code. There’s no risk in trying to cobble together an envelope that complies.”
• Acoustics. The Gig Harbor property is next to a busy highway, meaning outdoor conversation requires an elevated voice. Walker took some design steps to mitigate the din, like orienting the front of the home away from the noise and minimizing window exposure on the highway side. ICF turned out to be the real star: “It’s mind-blowing when you open and close the back door,” the architect says. “When you’re inside with the door closed, you don’t hear a thing. You wouldn’t know you’re living next to a highway.”
• Affordability. The project has caught the attention of local architects, builders, contractors, and affordable housing advocates. “This home meets the exact spec of a Habitat homeowner,” Kinchy says. “This is safe, clean, and affordable housing, just right for the teachers, firefighters, and working-class folks we serve.”
Learn more about how zero-carbon ICF construction can transform the sustainability of your next project.
This project is part of a wider initiative between the Build with Strength coalition and Habitat for Humanity International to construct at least 50 sustainable concrete homes in 50 states in 5 years. The partnership currently has 76 homes in various stages of construction in 33 states in under 2.5 years.
Gig Harbor project partners include: Heidelberg Materials, Washington Aggregates & Concrete Association, Airfoam Industries, Brundage Bone Concrete Pumping, Quad-Lock, SolidCarbon, Clark Construction, Insulating Concrete Forms Manufacturers Association, and American Concrete Pumpers Association.
