Timber house design to push sustainable building
Researchers around the world are seeking ways to make buildings more efficient and less dependent on emissions-intensive materials. This MIT project using timber is no exception.
The Longhouse, developed through an MIT class, is an energy-efficient design for a large community building that uses massive timbers made of conventional lumber laminated together – like a kind of super-sized plywood.
The design will be presented this October at the Maine Mass Timber Conference, which is dedicated to exploring new uses of this material to build safe, sound high-rise buildings.
John Klein, a research scientist in MIT's architecture department who taught a workshop called Mass Timber Design that came up with the new design, explains that 'in North America, we have an abundance of forest resources, and a lot of it is overgrown. There's an effort to find ways to use forest products sustainably, and the forests are actively undergoing thinning processes to prevent forest fires and beetle infestations’.
The structure designed by the class uses massive beams made from layers of wood veneers laminated together, a process known as laminated veneer lumber (LVL), made into panels 15m long, 3m wide, and more than 6 inches thick. These are cut to size and used to make a series of large arches, 12m tall to the central peak and spanning 15m across, made of sections with a triangular cross-section to add structural strength. A series of these arches is assembled to create a large enclosed space with no need for internal structural supports. The pleated design of the roof is designed to accommodate solar panels and windows for natural lighting and passive solar heating.
'Each arch tapers and widens along its length because not every point along the arch will be subject to the same magnitude of forces, and this varying cross-section depth both expresses structural performance while encouraging materials savings,’ said Demi Fang, an MIT architecture graduate student who was part of the design team.
The arches would be factory-built in sections, and then bolted together on site to make the complete building. Because the building would be largely prefabricated, the actual on-site construction process would be greatly streamlined, Klein says.
'The Longhouse is a multifunctional building, designed to accommodate a range of event scenarios from co-working, exercise classes, social mixers, exhibitions, dinner gatherings and lectures,' Klein said.
Whereas the production of concrete, used in most of the world's large buildings, involves large releases of greenhouse gases from the baking of limestone, construction using mass timber has the opposite effect, Klein claimed. While concrete adds to the world's burden of greenhouse gases, timber actually lessens it, because the carbon removed from the air while trees grow is essentially sequestered for as long as the building lasts. 'The building is a carbon sink,' he said.
One obstacle to greater use of mass timber for large structures is in current US building codes, Klein said, which limit the use of structural wood to residential buildings up to five stories, or commercial buildings up to six stories. But recent construction of much taller timber buildings in Europe, Australia, and Canada – including an 18-storey timber building in British Columbia – should help to establish such buildings' safety and lead to the needed code changes, he hopes.
Even buildings taller than 20 stories should ultimately be practical with this technology, he says. One of the largest mass timber buildings in the US is the new 7,618m2 John W. Olver Design Building at the University of Massachusetts at Amherst.