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News Article

Sustainable construction using mass timber

Prototype building designed to show that huge buildings can be built with wood

Nearly all types of buildings use vast amounts of energy and natural resources during their construction and operation.  With this in mind, researchers have long been trying to seek alternatives to make buildings more sustainable and which do not require emissions-intensive materials.  In the US, at the Massachusetts Institute of Technology (MIT), a project has developed a design for a large community building that utilises timber, one of the oldest construction materials in the world.  The structure, called “the longhouse” uses the lumber, which is laminated together. 

MIT research scientist John Klein, taught the Mass Timber Design workshop that developed the new design and explained 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.”

Wood tends to be considered as a suitable material for structures that are a few stories high, but not for larger structures.  Some builds are already using mass timber products for larger structures (products that are significantly bigger than conventional lumber) including medium-rise buildings of up to 20 stories.  According to Klein, buildings that are even taller that this could also use this technology.  One of the largest buildings made from mass timber in the US is the new 82,000-square-foot John W. Olver Design Building at the University of Massachusetts at Amherst.

But can tall wooden structures really be safe?  One of the main concerns people tend to have when they think of buildings made from wood, is the fire risk.  Klein explains that tests have demonstrated that mass timber structures can resist fire as well as, or better than, steel.  This is because wood, when exposed to fire, naturally produces a layer of char, which is highly insulating and can protect the bulk of the wood for more than two hours.  In contrast, steel can fail suddenly when heat softens it and causes it to buckle.

According to Klein, this natural fire resistance can be explained when thinking of dropping a lit match onto a pile of wood shavings, compared with dropping it onto a log.  The wood shavings will burst into flames, whereas the match will simply go out on the log.  In other words, the greater the bulk of the wood, the better it can resist ignition.

The structure that was designed by the research team uses huge beams made from layers of wood veneers that have been laminated together and made into panels 50 feet long, 10 feet wide and more than six inches thick.  They are then cut to size and used to make a series of large arches, 40 feet tall and spanning 50 feet across.  A number of these arches are assembled to create a large enclosed space without the need for internal structural supports.  The roof consists of a pleated design to accommodate solar panels and windows for natural lighting as well as passive solar heating.

Currently, most of the world’s largest buildings contain concrete, which releases greenhouses gases during the baking of limestone.  The researchers say that construction using mass timber has the opposite effect, as carbon removed from the air while the trees are growing is, in essence, sequestered for as long as the building lasts. 

One obstacle to the greater use of mass timber for large structures is the current US building codes, which restricts the use of structural wood for residential buildings to a maximum of five stories, or up to six stories for commercial buildings.  However, Klein says that the recent construction of much taller timber buildings in Europe, Australia and Canada should help to establish the buildings’ safety and could lead to changes in the US building codes.

The Longhouse design will be presented at the Maine Mass Timber Conference in October.

Further information is available on the Forest Science database.  Subscribers can retrieve over 380 records when using the search string "wood products" AND ("building materials" OR "building timbers")

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 28 August 2018
  • Source
  • Massachusetts Institute of Technology
  • Subject(s)
  • Forest products