Home Building: Stick Framing Is Here to Stay, and CLT May Be Next

Despite increased moves towards prefabrication in home building, stick-framing, whether using wood or steel studs, will persist because it is FLEXIBLE in the sense that it does not place limitations on size, configuration, or the style of a house. Combined with the ubiquity of the lumber and framing crews in the United States, it is not likely prefab (as in completed units delivered from the factory) will ever significantly penetrate the home building market.

Stick-framing has introduced many important prefabricated innovations over the last 60 years — gang-nail prefab trusses, glue-laminated beams, I-joists, and engineered lumber (LVL and LSL), just to name a few. Worth a visit, the Structural Building Components Association’s (SBCA) has a web page that compares old-style wood framing to newer methods using these more modern components. Also, the American Plywood Association (APA) has prepared a historical essay on the evolution of wood components. Add in other prefabricated components such as windows, pre-hung doors, and cabinets, and we see that conventional stick framed houses are, in fact, largely prefabricated.

In most instances, stick framing is NOT prefab when it comes to the framework, which of course, matters the most. The laborious task of nailing together sticks to form a structural frame is still the norm. The industry has introduced a multitude of steel brackets, tie-downs, straps, and more that do help when wood framed structures confront high winds and even earthquakes. But these techniques are not always successful, as witnessed in the destruction from recent Hurricanes Irma (US Virgin Islands, and many others), Maria (Puerto Rico) and Michael (Florida Panhandle).

The four HUB types (clockwise from the front): POST-BASE, TERMINAL HUB, INTERMEDIATE HUB, and BASE HUB.

HabiTek turns the platform wood framing model upside down. Instead of having framers install hundreds of steel elements, such as tie-downs and straps fastened in place with thousands of screws, HabiTek places the steel in a just a few components — HUBS, brackets, posts, beams — that are bolted together. Wood is reserved for infill: floors, walls, and roofs (with the exception of the Adapt-1 Beta Project). HabiTek’s primary modular structure is steel, making for very strong bones and much faster construction, and HabiTek’s resilient framework will not burn, rot, or warp.

In terms of wood construction, the new kid on the block is Katerra, a manufacturer of prefab wall panels, including cross-laminated timber (CLT) panels. Headquartered in Menlo Park, CA, Katerra is vertically-integrated in that they are the developer, general contractor, manufacturer, and supply most everything else involved with finishing a structure. While their target market is low and medium-rise apartment buildings, hotels, and office buildings, there’s no reason their CLT panels can’t be used for single-family homes. Like the HabiTek System, Katerra’s modular CLT panels are design flexible, with the only drawback being that heavy lifting equipment is required to position panels. This limitation would likely make CLT impossible in places like Puerto Rico, and certainly Haiti.

Cross laminated timber (CLT) panel being maneuvered into place with a crane. © D.R. Johnson, Green Building Advisor

With $850m in capital available, Katerra is currently in the process of building a major CLT manufacturing facility in the Spokane Valley, expected to be online later in 2019. Katerra’s modular CLT panels may be compatible with HabiTek’s steel frame module and could work nicely as infill for HabiTek’s frameworks. The possibility of rapidly enclosing a HabiTek framework with CLT panels is certainly worth exploring.

Happy New Year!