There's been a big movement in the energy-efficient and carbon-neutral design sector in recent years.
The initial primary design target has been to reduce operational energy usage (electricity, HVAC) because it was such a low-hanging fruit. The typical building constructed in the 20th century (and even 21st century) is pure crap in terms of energy efficiency. Their roofs and walls are leaky and lack insulation, and their windows leak tons of heat and air. So just making a building airtight, adding plenty of roof insulation & reflective roof material, and installing energy-efficient windows has done wonders in reducing HVAC needs.
Reducing carbon-usage beyond reducing operational energy usage is more difficult. The next major step is through reducing embodied carbon. Embodied carbon is the amount of carbon expended during the construction of the building, including methods and materials used. Both steel and cement manufacturing releases an exorbitant amount of CO2 into the atmosphere, some of the worst in any industry. So reducing the amount of steel and cement used in a building would drastically cut down on embodied carbon emissions.
This is where mass timber comes into play. Trees act as a carbon sink (up to a certain age). By using lumber instead of steel & cement, you are drastically reducing the initial embodied carbon in new construction.
Unlike modern wood-frame construction, mass timbers come in beam & column sections that are much, much thicker than a typical 2x4 or 2x8. This not only increases the inherent strength of the structural sections, but also makes it more fire resistant. When a fire occurs, the outside section of the mass timber chars, which helps protect the inner sections and helps maintain the strength of the mass timber.
Mass timbers are no longer a single solid piece of wood from a tree trunk. Old growth forests are protected, and newer lumber forests are still too young to produce such thick lumber. Instead, most mass timber consists of Cross-Laminated Timbers (CLTs), which are essentially made from several 2x4s glued & pressed into a single thick structural section.
You can read more about CLTs here:
https://www.naturallywood.com/produc...inated-timber/