By thoroughly explaining the design principles of Passive House and working with the needs of the homeowners, Cairn Collaborative’s YouTube video series is a great resource to see a Passive House come to life. The series, developed with In Balance Green Consulting, walks you through the construction process of the Bishop Passive House, a 2,900 square foot home in California that is pursuing Passive House certification and adhering closely to the standard’s design principles.
The Slab
Mike Horgan begins the series by talking through the layers from the foundation up to the slab: compacted fill, Glavel (insulated glass aggregate), a continuous layer of 15 mil Stego vapor barrier over all of the aggregate, mastic around the edges, and then concrete poured directly on top of the vapor barrier. For the WRB system, Cairn went with an all-in-one approach consisting of half-inch CDX for the wall sheathing, with 475’s ADHERO exterior membrane. In Mike’s words, ADHERO is “the best WRB available on the market!” By using 475’s CONTEGA MULTIBOND adhesive to attach right to the slab, the airtightness system has already begun. Next, the ADHERO wall membrane is applied and attaches to that adhesive, continuing the airtight envelope. ADHERO is a fully self-adhered membrane that provides many benefits: bulk water defense, airtightness, and moisture control.
The Cairn team goes on to explain the importance of having insulation under the slab as well as their intentional efforts to steer clear from foam (see our “Foam Fails” blog series for more on that). This insulated slab provides a thermal break between the ground and the slab. Therefore, a cold evening won’t always mean a cold floor, as the air bubbles in the Glavel cause the temperature to stop moving from the ground into the slab, which creates said cold floor. Glavel is a 100% recycled glass aggregate with a porous texture that comes in a rock shape about 3 inches tall. The material is very lightweight and it can be laid down quickly.
The Wall Assembly
The wall assembly for Bishop Passive House consists of 2x6 framing filled with blown-in cellulose, CDX sheathing wrapped in ADHERO, with continuous GUTEX wood fiber board insulation on the exterior strapped with a vented rainscreen that gives a ½ in air gap. It's important in Passive House construction to not sacrifice views and daylighting for airtightness and performance. High quality windows let there be a balance and allow us to highlight the reason that a client bought a property in the first place: for the extraordinary views.
Thermal Insulation
Exterior Insulation (a.k.a. the puffy jacket) provides it with a lot of benefits: comfort, temperature regulation, and sound attenuation are just a few. Understanding the psychrometric chart can help illustrate just how much this simple step can boost the efficiency of the home. The Bishop House used 1.5” Gutex Multitherm woodfiber insulation to wrap the entire exterior of the conditioned envelope. GUTEX is made of wood and is tongue and groove, so snapping a reference line around the building and then going up from there makes it easy to assemble. It is attached with staples but further secured with furring strips. GUTEX is not only healthier for inhabitants and installers, but also has a low global warming potential, making it a great product for the planet as well.
When constructing an airtight home, transitions are the spots that will make or break the project. In typical construction, these are the places that could turn an otherwise comfortable home into an oven or an ice box. As tedious as these details may be, they are crucial for achieving that continuous insulation and airtight boundary. Thermal bridges can be thought of as an uncontrolled highway allowing for temperatures to move in and move out. Because one of the main goals of Passive House is to keep control of the temperature, being mindful of thermal bridging is key. Cairn was able to implement all of the Passive House principles into this project, while keeping costs in mind and the homeowners very happy. We’re huge fans of Cairn Collaborative’s work and can’t imagine a better example for our products. We hope you subscribe and keep watching their YouTube channel for more.
