Cross Laminated Timber (CLT) has been in use in Europe for years and is finally making its way to North America. This fast-build, environmentally friendly construction is making a push to compete in the marketplace. Read on to learn about one of the newest building technologies and the acoustical properties associated with it.
What is CLT?
CLT, or Mass Timber, is a wood structure that is made up of planks of wood that are stacked on top of each other and glued together, with each layer being set perpendicular to the previous layer. The number of layers that are used depends on the thickness and structural requirements of the project. The panels come in a range of thicknesses up to one foot. By setting these layers perpendicular, structural rigidity of the panel is obtained in both directions.
All CLT panels are prefabricated and designed to handle the precise structural load required of it, whether a floor, ceiling, wall, or roof. These prefabricated panels are designed to incorporate door and window openings as well as routings for electrical and mechanical systems. When the panels arrive on the job site, they are installed almost like a large Lego kit.
So, are they good for acoustics?
CLT panels are significantly less massive than a concrete slab and are very rigid, which is not the best combination for good acoustical separation typically driven by both mass and decoupled structures. Therefore, CLT assemblies alone do not provide very good acoustical separation. A typical 7” CLT floor/ceiling assembly has airborne and impact sound transmission ratings of approximately STC-40 and IIC-26. That’s a long way from meeting minimum IBC requirements of STC-50 and IIC-50 between dwelling units. Improved acoustic separation can be achieved with additions to the CLT assembly including concrete toppings, resilient underlayments, and gypsum board ceilings.
CLT structures are also used as wall assemblies and have the same low acoustical performance issues. CLT walls can be improved by decoupling multiple panels or incorporating a stud and gypsum board partition in tandem with the CLT assembly.
So, if CLT isn’t excellent for acoustics, then why use it?
Unlike concrete, CLT has several environmental benefits. Its largest advantage is carbon sequestration – the timber acts as a carbon store and begins life as a carbon-negative material. Taking into account material, transport, site work and end-of-life, a steel-framed CLT building generates nearly half the CO2 emissions per square meter as a reinforced concrete one. Building with timber also reduces the overall carbon footprint as wood is a renewable resource and growing a tree is a low-impact method of production; it uses photosynthesis rather than machines. Trees are grown in abundance in the United States and don’t need to be imported from abroad, reducing the amount of energy expended on shipping.
In addition to its environmental benefits, CLT manufacturers claim that by using prefabricated pieces, the construction process is significantly faster versus conventional construction, which leads to reduced construction costs. While the up-front cost of the material may be more expensive, that cost is made up quickly due to expedited construction.
Check out this video on how CLT is made, here.
So, while sticks and stones might break your bones, Cross Laminated Timber will be lean and green, and treated properly – an acoustical sound machine!