Tall timber buildings are on the rise. Design teams around the world are taking advantage of ever-evolving mass timber technologies, resulting in taller and taller structures. Building off our recent article exploring the future of high-rise buildings, we’re taking a deeper dive into new emerging timber technologies and the advantages of building taller with wood. This tutorial explores how to make tall timber structures a reality.
The Council on Tall Buildings and Urban Habitat (CTBUH) provides definitions for what constitutes “tall” around the globe. The CTBUH defines the materials from which tall buildings are comprised. Buildings constructed from timber are permitted through “the use of localized non-timber connections between timber elements” and in some cases a “floor system of concrete planks or concrete slab on top of timber beams” since timber still acts as the primary structure. These tall wood projects can be either heavy timber or mass timber.
When building tall, the structural system must be taken into account, including ductility, load paths, and transfer and uplift forces. You should consider connections in the building to address ductility. Load paths can cause elements to experience compression, tension, bending, torsion, or shear. For tall wood buildings, the structural elements are particularly susceptible to shrinkage, and you can address this by utilizing construction where wood grain is parallel to the load path. Stairs or elevator shafts can also be used to transfer loads. Because they are often lighter, wooden tall buildings are susceptible to uplift.
The IBC classifies five major construction types, each with subcategories and maximum permissible heights. Type I-A (Unlimited), I-B (180′), II-A (85′), II-B (75′) are for noncombustible construction. Type III-A (85′), III-B (75′), V-A (70′), and V-B (60′) are for light frame wood construction. Type IV-HT (85′) pertains to heavy timber. Each subcategory has its own fire resistance requirements, and these height limits are only permitted on buildings equipped throughout with an NFPA 13 sprinkler system.
After the structural and code considerations are met, you should address fire protection, acoustic, seismic, and thermal standards. Even though mass timber members have natural qualities that resist fire, there are additional steps that can be taken for further protection. Mass timber or heavy timber products can be sheathed in gypsum wallboard, a fire-resistant material, either fully or partially. If done partially, the structure and the ceilings of the building are normally covered. For sound, look to floor, ceiling, and wall assemblies. Likewise, from a thermal standpoint, wood does not need a thermal break between the structural and exterior envelope. In some cases, mass timber can store solar heat energy during the day and release it at night, reducing energy loads.
Looking to dig deeper to build taller with wood? Learn with Think Wood’s continuing education unit Design and Construction of Taller Wood Buildings. Take the Course or check out Wood Works Mass Timber Design Cost Optimization Check List to help you with your next project.
Author: Eric Baldwin
This article was first published in Arch Daily and is republished with permission.