Washington, DC (Sept. 24, 2010) – As a result of a strategic alliance between the National Center for Sustainability and MDS10 Architects of Asheville, North Carolina, the United States will soon have its first “pure” cross laminated timber (CLT) structure—a 78-foot bell tower adjacent to Myers Memorial United Methodist Church in Gastonia, North Carolina—as well as a showpiece for demonstrating the environmental, performance and cost benefits of this unique wood product.
‘Sustainable Cross Laminated Technologies LLC” (SCLT) was formed earlier this year to initially import, and eventually produce CLT, which is widely used in Europe, for use by North American design and building professionals. Utilizing small diameter timber from sustainably managed forests, CLT is comprised of boards stacked together at right angles and glued over their entire surface. The result is an exceptionally strong—and environmentally sustainable—product that significantly increases the possibilities for wood design and construction.
“In addition to the fact that wood is the only major building material that’s renewable and sustainable, life cycle assessment studies show that wood products are responsible for less air and water pollution, and less greenhouse gas emissions than other materials,” said Steve Cochran, SCLT’s chief sustainability officer. “The process to manufacture CLT is energy-efficient and low polluting, prefabricated panels eliminate jobsite waste, and CLT buildings are proven to maintain their ambient temperatures with less energy. From an environmental perspective, the availability of CLT in North America is a huge step forward in sustainable development.”
“The 78-foot bell tower includes 70 feet of CLT above a three-foot concrete foundation—which, because of CLT’s light weight, is substantially smaller than would have been necessary to support a tower built in steel or concrete,” said project architect Michael DeVere, who is also co-director of architecture design and research for SCLT. The tower is 12x12 feet and utilizes 4-foot panels of varying lengths, which are prefabricated at the manufacturing facility and assembled on site. The dimensions were chosen to allow the panels to be assembled in an “H” formation that provides natural openings for windows and doors.
“In Europe, thousands of CLT buildings have been constructed over the past decade—including an apartment building in London comprised of eight stories of wood over one story of concrete,” said DeVere. “Given its environmental, structural and economic benefits, we believe that CLT’s acceptance in the North American market will be swift and enduring. The bell tower in Gastonia is just the beginning.”
Using the nine-story UK building as an example, the architect of that project estimated that, between the greenhouse gas emissions avoided by not using steel or concrete and the fact that wood products continue to store carbon absorbed during a tree’s growing cycle, the building saved about 300 metric tons of carbon—which is the amount the building was projected to emit over 21 years of operation.
For comparison, the design team also presented the developer with concepts for two almost identical structures, one in CLT and the other in concrete. The wood structure was estimated to cost £1,420 per square foot (approximately $2,208 USD at today’s exchange rate) compared to £1,750 a square foot ($2,722 USD) for concrete, a savings at the time of 15 percent.
“In addition to lower material costs, the building was projected to weigh four times less than its concrete counterpart, which lowered transportation costs, allowed the design team to reduce the foundation by 70 percent and eliminated the need for a tower crane during construction,” said Greg Tolan, SCLT’s director of construction.
Particularly impressive was the fact that the architect proposed to shave five months off the typical construction process for this type of building—a goal he exceeded. It took four carpenters nine weeks to erect nine stories—and the entire building process was reduced from 72 weeks to 49. Erection of the bell tower in
Gastonia is expected to take 2-4 days and will take place early in November.
“In terms of structural performance, the bell tower is located in a 90 mph wind zone, and yet is projected to move only half an inch at its apex during even the highest wind conditions,” said Crawford Murphy, SCLT’s second co-director of architecture design and research who designed the project with DeVere. “However, because CLT is new to the U.S., the design had to undergo building code equivalency testing before it was approved by the City of Gastonia.”
The WoodWorks program, which provides technical support for architects and engineers using wood in non-residential buildings, is supporting the Gastonia project by contributing technical expertise via an independent building official whose role is to ensure that the structure meets all local building code requirements. The introduction of CLT in the U.S. is also being supported by the American Wood Council and APA – The Engineered Wood Association, which is leading the development of American National Standards Institute (ANSI) product standards. Medlock & Associates, PA of Asheville are the structural engineers for the project.
In collaboration with the architectural and engineering community, timber research organizations and forestry stewardship initiatives, the construction sector, higher education and building code organizations, SCLT will serve as catalyst, importer and ultimately the leading manufacturer and builder of CLT technology systems in North America. SCLT will also work with the Global Institute for Sustainability Technologies at Asheville-Buncombe Technical Community College to develop workforce training in the use of CLT.