If you know what Mass Timber means, you probably already know that that codes needed to help this new wood structural system be utilized in the US have been under development. If you don't really know, then read on:
Mass Timber is the use of wood to frame large buildings by layering 2X lumber, plywood style, into large panels and beams using various methods of lamination. This method holds the promise of taller wood frame structures, with reduced carbon footprint, and potential for reduced construction schedules and on-site labor. This method is being taken up in Europe but has faced resistance in the US, due in no small part due to the inability of local building inspectors to evaluate and inspect these structures. The updated codes permit these officials to do their work, and give designers a framework to work within.
Mass Timber can be considered to be structurally similar to precast concrete, which can be formed into slabs, beams and walls, and assembled by crane. A great advantage of Mass timber over precast is the reduced weight of the elements, which in turn reduces foundation costs. Both of these reduce the amount of concrete in the building which is a highly carbon intensive material.
Previously, these structures would have fallen under the "Heavy Timber" classification, which would limit construction heights to around 6 stories. The new codes permit significantly taller structures, up to 18 stories in some cases.
Yes. Wood burns. The new code takes that into account, and also takes into account the nature of these mass timber elements which have some natural resistance to combustion built in. Taller structures require redundant fire protection water sources, and requirements for structure longevity in fire conditions is substantial.
Mass timber structures have been constructed that utilize the wood structure as interior finishes, which can provide both economic and aesthetic benefits. Other structures are constructed and are visually indistinguishable from more traditional commercial buildings. There is an enormous range of design opportunity available, with potential economic and climate change reduction benefits. Take a look!