Mass timber is an engineered wood product formed by gluing or fastening wood panels in layers to achieve exceptional strength and stability.
The production is so versatile that it can be used as structural panels, columns, beams, load-bearing structures, or even for interior finishes.
The mass timber family of products includes cross-laminated timber (CLT), glue-laminated timber, structural composite lumber (SCL), nail-laminated timber (NLT), and dowel-laminated timber (DLT).
This article discusses the provisions of mass building construction as per IBC 2021 and how it is gaining popularity as an alternative to high carbon footprint building materials like cement and steel.
Mass Timber for Tall Wood Building Construction
In response to the growing interest in tall wood buildings, particularly constructed from new mass timber materials, the International Code Council (ICC) came up with a set of proposals to allow tall wood buildings in the International Building Code (IBC) 2021.
Based on this, IBC 2021 mentions three new tall wood building construction categories using mass timber or non-combustible materials. The maximum height limit, the details of Fire Resistance Ratings (FRR), and the non-combustible protection of the mass timber building elements are explained in the code.
The three categories of tall wood buildings that can be constructed using mass timber are:
- Type IV-A: Maximum 18 stories, with non-combustible protection on all mass timber elements.
- Type IV-B: Maximum 12 stories, limited area of exposed mass timber walls and ceilings allowed.
- Type IV-C: Maximum 9 stories, all mass timber permitted to be exposed (with a few exceptions, e.g., shafts) and designed for 2-hour fire resistance.
Hence, the 2021 IBC defines mass timber as “Structural elements of Type IV construction primarily of solid, built-up, panelized or engineered wood products that meet minimum cross-section dimensions of Type IV construction.”
The three types are based on already existing Type IV-HT, which is the heavy timber construction category, but Type IV-A, B, and C require additional fire-resistance ratings (FRR) and higher levels of noncombustible protection, as explained in Table-1.
Benefits of Mass Timber in Construction
Mass timber and its use in construction offer various properties and benefits over other building materials like concrete and steel. The main benefits of mass timber in building construction are:
1. Mass Timber is Fire Resistant
During fires, the exposed surface of mass timber chars on the outside, forming an insulating layer that protects the interior wood from damage. Based on the country's regulations, the mass timber may require protection using gypsum wallboard, which would help achieve damage-free performance during a fire.
2. Mass Timber is Structurally Strong
Mass timber combines multiple load-bearing wood panels bonded by glue, dowels, or nails, making them highly strong and stable. The layers of wood panels in a mass timber can be compressed in parallel or perpendicular directions based on the desired structural integrity.
3. Mass Timber is Light in Weight
Mass timber is light in weight and has high strength ratings compared to concrete and steel. Mass timber buildings weigh approximately 1/5th of the weight compared to other concrete buildings, thus reducing the foundation size, inertial seismic forces, and embodied energy. They perform well during seismic activity due to their high strength-to-weight ratio.
4. Mass Timber is Sustainable
Lumber is the main raw material used for mass timber production. It is not only sourced for construction practice but also sustainably harvested using the best practices.
Using mass timber instead of steel would reduce carbon dioxide emissions by 15 to 20%.
5. Mass Timber Construction is Cost-efficient
Mass timber is not inexpensive, but in terms of overall performance, it is 25% faster to construct and requires 90% less construction traffic compared to concrete building construction.
Mass timber building elements can be prefabricated and assembled on-site, especially for projects with shorter timelines. This, in turn, results in safer construction sites.
Mass timber construction inspires innovation. As per WoodWorks reports, in the U.S. since 2013, 1300 multifamily, commercial and institutional projects have been completed, and some are in design progress using mass timber or heavy timber. Hence, this technology is on the rise because of its benefits in terms of strength and sustainability.
FAQs
Mass timber is an engineered wood product formed by gluing or fastening wood panels in layers to achieve exceptional strength and stability.
The mass timber family of products includes cross-laminated timber (CLT), glue-laminated timber, structural composite lumber (SCL), nail-laminated timber (NLT), and dowel-laminated timber (DLT).
IBC 2021 mentions three new tall wood building construction categories using mass timber or non-combustible materials. The maximum height limit, the details of Fire Resistance Ratings (FRR), and the non-combustible protection of the mass timber building elements are explained in the code.
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