In fact, Hagerman says, Passive House has no prescriptive requirements; if a building’s heat load is less than 4.75 kBtu per square foot per year and total energy use is 38.1 kBtu per square foot per year while air exchanges are at 0.6 per hour at 50 pascal the building has met the standard. Hagerman adds there are stringent comfort, hygrothermal and durability aspects important to the design and certification process. Glasswood, which is approximately 3,000 square feet, was a prime candidate for a Passive House retrofit because it was in a very dilapidated state. “The entire perimeter of the building was rotten through the rim joist,” Hagerman remembers. “We had to build the floor system on the first floor all the way out to the exterior sheathing, and then we were able to take out most of the interior walls and replace them with beams. We were essentially left with two very large open spaces that we could improve upon.”
Despite almost starting from scratch, Hagerman still encountered challenges with retrofitting the space. He and Thomas decided to make the second floor of the building the home performance and building science division’s office; the first floor would house Xico, a Mexican restaurant Thomas co-owns. Because of the challenges presented by the high loads of the restaurant and commercial cooking equipment, it was decided early on that they would not seek certification for the first floor. However, the same Passive House principles were adopted and applied to Xico, making it an exceptionally high-performing restaurant space. (For an explanation about Xico’s high-performance characteristics, visit Hammer & Hand’s website.)
In addition, a parapet wall threatened to derail the Passive House airtightness plans for the second floor. “I didn’t have any cost-effective way to retrofit up and over the existing parapet wall and roof diaphragm with the airtight layer,” Hagerman remembers. “Retrofitting an airtightness layer through the existing parapet wall would have been extremely challenging, so I was really stumped until I realized I should simply move the airtight layer to the inside of the existing framing and frame a service cavity inboard of that.”
The Details
Hagerman describes the 1,400-square-foot second-floor Passive House space as simple with 10 large windows and a large concrete floor. The 12-inch-thick wall construction from the outside is constructed with siding, a rainscreen, a layer of 60# paper, a layer of fiberglass-mat gypsum panels over 2-inchthick expanded-polystyrene (EPS) insulation and a 3/4-inch structural sheathing CDX plywood over the existing 2- by 4-inch walls. A layer of 1/2-inch-thick oriented strand board (OSB) and air-sealing tape was placed on the inside face of the existing framing and then another 2- by 4-inch wall assembly layer, acting as a service cavity to run pipes and wires, was installed. (This OSB layer and nonstructural service cavity also were installed on the ceiling. OSB and tape were used as the air barrier at the floor.) Finally, the service cavity was covered with drywall.
The space’s triple-pane windows include a fiberglass frame with EPS insulation inside the frame. The European-style tilt-and-turn windows are installed in the center of the 12-inch wall assembly with a vapor permeable liquid-applied flashing system. A transition sheet material is embedded into the liquid-applied flashing to interface with the 60# paper.
“Liquid-applied flashing is a standard detail on all of our projects—big or small,” Hagerman notes. “The products and strategies were designed to become the membrane that wraps inside the window opening and forms a seamless waterproof bucket that remains vapor permeable. Then, the window is installed in the waterproof bucket and sealed on the inside and left open to the outside, so if and when the window leaks, this moisture can drip onto the sloped waterproof sill and drain out to the face of the rainscreen.”