We have our Green Building Code in California, which is unique to the world. To truly be green, other parts of the Building Code needs to change or at least be more flexible to allow greener methodology to really work. This has always been true for any changes in technology. The building code is reactionary to these changes and never proactive. When the use of hay bales or mud/dirt was used as a green material, there was and still is nothing in the codes that really permit this. How do these materials comply with standard building material testing? Can any of these materials withstand the seismic/lateral loads we apply in California?
Wood, like hay bales and mud, is one of the most sustainable materials we have as well as being cost effective.
Wood is a renewable crop and it’s a carbon sink, sequestering the carbon dioxide it absorbs during growth, even after it has been turned into lumber. A large wood building stores tons of carbon while an equivalent steel and concrete structure would generate tons of carbon dioxide during production. Mathematically, the net savings by using wood would be the sum of the two values (wood used – tons + concrete/steel – tons not used).
So what if we build our high-rises out of wood – this would be a very green building! The biggest drawback to wood is its flammability. That is the primary reason the code limits the use of wood in building to a certain size (height and area). What if we changed the concept of wood from standard balloon or western platform framing to something more fire resistant; should we allow a wood high-rise (greater than 75-feet) building? One of the approaches would be to us a highly engineered wood product called Cross Laminated Timbers (CLT). It is like Oriented Strand Board (OSB) in what would be using 6 inch thick wood panels: plywood on steroids. This would be more like heavy timber construction. Heavy timber has a unique fire resistant property. When wood burns, it chars on the surface. The charring acts like an insulator to the interior of the wood member. During a structure fire the exposed wood surface will be converted to char until the thickness of char provides a layer that then serves to protect the remaining structurally sound core of wood, which can continue to carry the building loads if appropriately designed.
This method of construction using CTL is already being used in England (up to nine stories) and proposed in other countries (up to 32-stories). As a thought experiment, Skidmore, Owings and Merrill’s design team came up with a 42-story building. Although developers are finding that there is a cost saving using CLT instead of conventional steel and concrete, the thought is that people may be unwilling to use or buy within this type of construction.
The biggest and hardest sell is to those enforcing the current building regulations. The height of a highrise was based on the ability of firefighting equipment being able to reach an occupied floor/story. To compensate for the increased height, additional fire protection features are required by the code. (The so called high-rise package.) This includes automatic sprinklers with emergency power and water supply, additional fire departments access. All of these elements should be continued in a wood high-rise building, but is this enough to convince the fire service equivalent to what we have now? Note that historically high-rise buildings are one of the safest structures we have. For this concept to move forward, designers, developers along with the enforcing entities will need to work together to make this happen.
The building codes were originally generated as a response to catastrophic fires that burned down whole cities. The elimination or mitigation of combustible construction was a driving force in code development. Now, with sprinklers, modern fire departments, and application of fire-resistant materials the combustibility of building materials is much less critical. This begins to open the possibility that safe tall buildings can be made out of what are today considered to be combustible materials. The advantage of these materials is that they are renewable and can be locally sourced. CLT materials also have unique properties similar to heavy timber that can be considered to make them naturally fire resistant without added materials, thus reducing material use. They also have the ductile properties of wood that can make these tall building materials perform well in seismic design.
The biggest issue for any new materials for code allowances is tied to the inherent resistance to change in the code development and code enforcement community. There is very much a mentality of fighting prior wars that leads to resistance to innovations. The remedy for this is data gathering through testing and allowance for providing buildings under alternate means to get real buildings in place to demonstrate that they can perform well. Architects will need to work with innovative clients and innovative material suppliers to move these new ideas forward.