Wood is perhaps the greenest building material; it is a renewable resource that absorbs carbon dioxide as it grows, which is sequestered in the wood when it is cut into building materials. But until recently its use was limited to low rise structures due to concern about the fire hazard.
But it has been known for centuries that heavy timber actually performs better in fire than structural steel; a layer of insulating and fireproof char forms on the outside of it when it burns, protecting the structural integrity of the wood. (It is designed bigger than it needs to be to allow for this char layer.) The recent development of cross-laminated timber creates a building material with all of the virtues of heavy timber without the need for the big trees. We've previously shown Waugh Thistleton's CLT building in London, 9 storeys of wood.
Now a new Canadian study demonstrates a hybrid system that has been engineered for buildings up to thirty stories. In Tall Wood (PDF Here), Author and architect Michael Green makes THE CASE FOR Tall Wood BUILDINGS: How Mass Timber Offers a Safe, Economical, and Environmentally Friendly Alternative for Tall Building Structures.
He starts off on the wrong foot with (I think) a dreadful name, FFTT, standing for "Finding the Forest Through the Trees".
The acronym speaks to the idea that much of the sustainable building conversation is focusing on minutia. While even the minutia contributes and is important, the big systemic change ideas are what we believe will be necessary for the built environment to tackle the scale of the climate change and housing demand challenges facing the world. FFTT is a contribution to hopefully many significant shifts in the way we approach buildings in the next decades. The goal is simply to focus on the forest but never forget the trees.
But after that he reaches for the sky.
The structural details of FFTT as a “strong column – weak beam” balloon-frame approach using large format Mass Timber Panels as vertical structure, lateral shear walls and floor slabs. The “weak beam” component is made of steel beams bolted to the Mass Timber panels to provide ductility in the system.
The system differs from pure CLT plays in that it also uses Laminated Strand Lumber (LSL, trade name Parallam) and Laminated Veneer Lumber (LVL). But the reasons for using wood in whatever form remain the same:
Wood is typically the best principal material available for building structures with respect to embodied energy use, carbon emissions and water usage. Sustainable forest management and forest certification are a necessary precursor to the increased use of wood. The ability of the public to embrace an increase in wood buildings comes with a strong understanding of the overall impact on BC, Canada and the world’s forests. Deforestation is a critical contributor to anthropogenic climate change. The concept of using more wood will only be fully embraced when the harvesting of wood is understood to be truly sustainable and responsive to the environment.
Sustainably harvested wood is the resource that lasts forever, employs local trades and minimizes shipping. Thanks to the Mountain Pine Beetle, we have more of it than we could possibly use.
Architect Michael Green and Engineer J. Eric Karsh have produced a remarkable 240 page document. Furthermore, they could have patented or licenced it but are giving away all of their research under a Creative Commons licence, writing:
The scale of the opportunity contained in these solutions is enormous, and there will be meaningful opportunities for some organizations, companies and individuals to profit from pursuing these ideas. The decision of the authors and originator of these ideas is to encourage an Attribution Non Commercial Share Alike approach (see below for definition) that encourages adoption of FFTT CC into mainstream building practices. This decision underscores our belief that these ideas are stepping stone concepts to the types of systemic change necessary to address climate change issues in the building industry with the increased use of sustainably harvested wood in building structures.
Their work may well change the nature of construction in much of the United States and Canada, where there is lots of wood and a lot of underutilized infrastructure and underemployed workers thanks to the crash in the single family housing industry. Green and Karsh may be planting the seeds of a construction revolution.
Download the big (31MB, 240 Pages) PDF here