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A net-zero mass-timber building

Designed by Generate Architecture and Technologies, a start-up company out of MIT and Harvard University, and design and construction company Placetailor, a five-storey building will be constructed in Boston, U.S., made from cross-laminated timber (CLT), said to be so energy efficient that its net carbon emissions will essentially be zero.

While certainly not the first of its kind, the construction in Boston will be one of the largest residential buildings in the U.S. made of CLT, thanks to innovative construction methods. The building will be assembled on site mostly from factory-built subunits, using large scale wood components known as mass timber. This type of components potentially make buildings of up to 18 storeys high possible.

Generate Architecture and Technologies modelled nine different versions of an eight-storey mass timber building, along with one steel and one concrete version of the building, each with the same overall scale and specifications. The analysis showed that materials for the steel-based building produced the most greenhouse emissions; the concrete version produced 8 percent less than that; and one version of the mass-timber building produced 53 percent less.

The most heard counterargument against building with wood is the fear of it being a fire hazard. However, tests have shown that rather than burning up, mass timber buildings retain their structural strength longer than a comparable steel-framed one. This is because the large timber elements, often 30 cm (1 ft) or more thick are made by gluing layers of conventional dimensioned lumber together. The wood chars on the outside, and this layer provides good insulation and protects the wood for an extended period. By contrast, steel buildings can collapse suddenly when the temperature of the fire approaches steel’s melting point.

Generate and Placetailor developed a kit-based approach, called Model-C, which allows the use of preconfigured modules, assembled in different ways, to create a wide variety of buildings of different sizes and for different uses. The subunits can be built in factories in standardised processes, and be assembled on-site, minimising construction time.

Because the thick wood structural elements are naturally very good insulators, the Boston building’s energy needs for heating and cooling are reduced compared to conventional construction. They also produce very good acoustic insulation for its occupants. In addition, the building is designed to have solar panels on its roof, which will help to offset the building’s energy use.

Photos: Generate Architecture and Technologies