S2. Ep. 09: GreenBox®, an Innovative Mass Timber Floor System
This episode introduces GreenBox®, a prefabricated mass timber cassette system that reimagines how timber floors are manufactured, installed, maintained, and reused. Paul Becker and Kristina Rogers hear from Harry Crofton, who explains how cassette construction shifts work from the jobsite to the factory, where components can be built with tighter tolerances, greater quality control, and without exposure to weather or site constraints. The result is a system that can cover longer spans and be lifted into place quickly to speed construction. The discussion compares GreenBox with conventional CLT floor systems, focusing on how its plywood skins, glulam joists and specialized fill work together to optimize structural capacity, services integration and coordination, acoustics, and vibration control. Also discussed are the system’s fire performance and superior moisture-management detailing. Rather than solving each performance issue with added layers, GreenBox integrates multiple functions into one lighter, more efficient assembly. The episode also covers the benefits of GreenBox over the full life of a building and beyond: simple to repair, replace, and modify, it can also be easily disassembled and reused in circular construction. Key Insights GreenBox® is designed as an integrated mass timber floor system. Rather than treating structure, acoustics, vibration, and sustainability as separate design challenges, GreenBox combines these functions into one prefabricated cassette assembly. Prefabrication improves quality, speed, and consistency. By moving more work into a factory setting, GreenBox components can be built with tighter tolerances and then installed more efficiently on site. The system offers a potential alternative to conventional CLT floors. GreenBox uses glulam joists and oriented strand board (OSB) to create I-sections, allowing long spans with much lower volumes of timber than would be required with a solid wood panel. Acoustic and vibration performance are central to the system. The specialized filling helps address two common challenges in timber floor design: sound transfer and footfall-based vibration. Moisture management is integral to the design. GreenBox uses a two-line moisture-defense strategy, with sealed upper joints to limit water entry and breathable lower joints that allow any moisture to escape. Performance validated through testing. Because the new system pushes beyond routine assumptions, fire performance was validated through physical testing. Circularity is a long-term value proposition. GreenBox is designed to be lifted into place, removed, reused or modified over time, supporting a more adaptable kit of parts approach to building design. Topics Covered How GreenBox® works as a prefabricated mass timber floor system How timber cassette systems can improve construction speed and consistency How GreenBox compares with conventional CLT floor assemblies How GreenBox floors can work well for big bays and long spans in large commercial and residential buildings Why acoustics and vibration matter in mass timber floor design How integrated systems can reduce material use and embodied carbon How acoustic and vibration performance, moisture control and services coordination affect adoption Why reusable structural systems are important for circular construction Thornton Tomasetti has partnered with National Timber Systems to produce GreenBox in the UK









