Integration of Three Wood-Based Products – GWC Mag

The design goal for this wall and roof assembly was to use three emerging European wood construction technologies that are starting to enter the U.S. market: cross-laminated timber (CLT), wood fiber insulation, and heat-treated wood siding. The objective was to maximize the building’s performance by creating a tight (R-38 wall, R-60 roof, .8 ACH50), resilient enclosure, while driving down the project’s carbon footprint by using biogenic, carbon-storing, structural, insulating materials.

The 100-mm-thick CLT panels provide a highly exact structural system, and the interior finish. Based on our BIM models, they were pre-cut by KLH in Austria and installed onsite in a matter of days. The wood fiber insulation was field-installed (9-1/4 in. in the walls, 16 in. in roof)—although we have discussed combining the CLT panel with our wood fiber board product to create one pre-fab assembly package. Actually, our vision for the second-generation panel includes CLT, wood fiber insulation, windows, WRB, and strapping. These assemblies would be pre-fabricated at OPAL Build in Belfast, Maine, and designed to be delivered onsite ready to go up, like the current iteration of panels.

A few notes on materials

The CLT panel is easy to handle and highly vapor permeable (0.05 to 0.6 U.S. perms); and the thick layer of exterior insulation we add can be carved out to integrate gutters, downspouts, and electrical runs. Because CLT and wood fiber insulation are both wood-based products they manage moisture similarly, creating a vapor-open assembly that allows moisture to pass through without getting trapped. This contrasts with combining a wood structural system with a foam plastic insulation layer that has no permeability and could result in moisture getting trapped in the assembly, potentially causing rot or mold.

The CLT is also the air barrier for both the roof and wall. The panel-to-panel joints are…