In our quest for robust, simple and cost effective approaches to high performance building, the I-joist outrigger assembly provides powerful solutions. Similar to a Larsen truss or a modified Larsen truss, the depth of the I-joist is ideal for providing needed depth and support for high insulation values.
Not only should we learn the lessons of advanced framing, but also the usefulness of continuous insulation and airtightness, which basic building science tells us will achieve greater efficiency and sustainability. In the 21st-century, we need to be more aggressive and view each new building as an opportunity to help fight climate change.
The I-joists form the ribs of a “parka” that is hung step-by-step on a traditional wood frame construction. The traditional wood frame can be platform or balloon framed with 2x4s wrapped in sheathing. The sheathing serves a traditional structural purpose, and if ¾” thick may serve as the primary air barrier and inboard vapor control. Consequently the 2x4 structural zone becomes a very robust and flexible service cavity where wires and pipes may run and outlets placed without penetrating the primary air barrier.
The I-joists are screwed onto the box, hung like a cabinet might be, and allow for perfect alignment of same-sized construction elements, with less human error than elements built on-site. As there is sheathing incorporated at the 2x4 box to provide stability, no more sheathing outboard is required, and a membrane can be used instead. In heating dominated climates the membrane should be vapor open. The membrane should also be reinforced to support dense-pack cellulose or fiberglass, with SOLITEX MENTO PLUS, which also serve as a secondary air barrier.
In the 21st century, our wood buildings also need to be made as energy efficient as possible to help fight climate change. Their operational energy use should be reduced to Passive House levels that can result in net zero emissions. This can be done safely and robustly. We can make them Smart Enclosures.