Passive House Wall Section Development, Part I
A three part series on making a passive house wall that’s leaner, faster, lighter, flatter, and less “holey” than thou. What’s the key element to developing a leaner, faster, tighter, less expensive Passive House envelope? Surround it with smart, skeptical people. It’s a formula that has worked well for GO Logic, where we’ve continually fostered a collaborative environment between our design team and the builders in the field. The resulting communication among our team makes for insightful, improbable solutions to the inevitable speed bumps that occur on building projects. But the real fun starts when we see how quickly this feedback loop can enable an iterative, agile design process— an approach that is inherently necessary when building on the leading edge of building technology in the United States. With this three-part blog series, we’ll delve into the How, the Why, and the When of our work with Passive House prefab in North America, and how we are pushing the available technology forward. We are making these hard-won lessons available to all interested parties for the betterment of all in the Passive House community, because we believe Passive House construction to be the way to build in the 21st century. It is also a relatively accessible standard for established builders: Passive House construction requires only a modest set of modifications to traditional building practices to achieve a staggering 80% reduction in energy consumption. 
Modern building science dictates that the “perfect wall” follow a few simple guidelines: a structural system to hold things together, some control layers for water, air, vapor, and temperature—to keep what’s outside out and what’s inside in—and some cladding to dress it up and to protect those control layers. From our first project, our wall design has adhered to these “perfect wall” criteria, but has grown with each project to become more durable, more efficient, and more cost-effective to construct. A brief history of GO Logic Our first Passive House was the first constructed in Maine, in 2010. The building consisted of a structural timber frame and a 2X4 service wall with blown-in cellulose insulation, with SIPs providing the bulk of the insulation on the exterior of the timber frame. (For those left wondering, SIP stands for Structural Insulated Panel, or, in layman’s terms, a big foam sandwich on OSB bread). The interior face of the SIP was considered the air and moisture barrier in this wall section, which meant that the air-seal had to travel around at several locations in the building, adding to the labor costs (and requiring a lot of tape!) 
As many know, SIPs are a great building solution; they are erected quickly and provide shear bracing to the frame and a nailing surface for the exterior cladding, providing a one-size-fits-all solution to residential construction. However, they do have their drawbacks: they are large, cumbersome to install and airseal, and often sourced from another company well outside the builder’s neighborhood. Furthermore, panels usually required modification on site to match the architectural plans, which detracted from the efficiency of using SIPs in the first place. These factors were limiting the geographic footprint to which we at GO Logic could reasonably deliver a building envelope. 
GO Logic has steadily moved toward prefab as a cost-effective, efficient way of delivering a high-quality building envelope. During this process we began designing a new wall from the foundation up, questioning every detail, to see where we could simplify, shed weight, reduce labor and introduce environmentally friendly materials where possible. As much as we loved the timber frame, stud framing proved to be a more cost-conscious way of building, and we all knew that the SIPs wouldn’t be a great fit for prefab. 
We began looking beyond SIP panels and EPS foam for other insulation options, and were soon confronted with a great number of options in many different flavors. There’s an insulation to satisfy every shade of builder, from all-natural insulation in the form of expanded cork and batts made from sheeps’ wool, to low-carbon options like cellulose or recycled denim, to—our house favorite—the industrial by-product known as rock wool. Rockwool (commonly marketed under the name Roxul) is non-combustible and hydrophobic, a material made partly from the slag left over from making steel. The main component of Roxul is basalt, melted and mixed with the slag and spun, like cotton candy, into board or batt form. It can be cut quickly and quietly with a serrated knife, and provides a respectable R4 per inch. It mops up sound as an acoustic insulation, and critters largely ignore it because they—like us—don’t enjoy chewing on rock. (That said, it doesn’t contain pesticides or additives to fend off pests, so we take care to keep it protected!) But most importantly, using rockwool allowed us to separate the airseal from the bulky insulation layer, which could greatly simplify the panelization process. Next, we’ll talk about integrating that insulation into our first prefab houses; our first forays into panelization and the lessons that came with those projects. -Andrew Frederick, Foreman
