Cross-laminated timber is a wonderful way of using up all those billions of board-feet of pine-beetle kill lumber that's rotting away. Cut it, glue it and press it, and you have giant panels that can used for strong, earthquake resistant and yes, fire resistant construction. It already is a form of flat-pack prefabrication, but Seattle architects Weber Thompson take it one step further: They are proposing to go modular with it as well.
Until now, modular construction and CLT have been studied and executed in isolation, but never in this combination,” says [Associate Myer] Harrell, who has a passion for sustainable design and won the AIA Seattle Young Architect award in 2011. “In order to really gain momentum, we’ll need to formalize a code alternate or code revision with the City of Seattle, and then work with an eager developer and contractor who are willing to go outside the boundaries of conventional building,” says Harrell.
They explain why CLT is such an attractive material.
It is the sustainability and aesthetic aspects that appeal most to architects. When forested or recycled responsibly, wood has long been understood as a renewable resource with a net carbon reduction to the environment as analyzed in its overall lifecycle, things that neither steel nor concrete can claim. The ability to build more densely out of wood is a win-win for the green building movement. And, when detailed to expose the wood in walls and ceilings, CLT can help bring the warmth and beauty of wood finishes to high rises, achieving an honesty of structure to which architects often strive.
The case for going modular with CLT is not entirely convincing. CLT is already cut in a factory to the exact prefabricated panel size, usually up near the forests where the wood comes from and is shipped very efficiently as a flatpack. One would have to set up another factory closer to the site to assemble the modules, which are too expensive to ship long distances. CLT high-rises in the UK and Australia went up really fast, and had all the chases for electricity and holes for plumbing pre-drilled, so that the trades could do the on-site work more quickly and easily. Going modular also uses more material, as every unit has its own walls and ceilings; in traditional modular there is a 30% increase in the amount of wood.
Flatpack CLT prefab is a pretty impressive thing all on its own. The wonder of CLT construction is that it is already fast, it is terrific for lower buildings which are often on tighter lots (and where it is harder to swing a crane with a whole module than just a panel). I wonder if modularizing it isn't a technological step too far.
More at Weber Thompson, whose own offices are, I think, one of the most important and overlooked buildings in America.