Building Codes

Citing sustainable, economic and energy efficiency advantages, a movement to build taller with wood is gaining traction around the world. Development of new technology and building systems are supporting the use of wood in more applications, and its benefits are being recognized through updates to building codes. 

Today, builders have the opportunity to operate within the parameters of the recently approved 2015 International Building Code (IBC), which is beginning to be adopted in various jurisdictions all over the United States. Others are closely following research and testing that in the future will enable us to join other countries where buildings over 10 stories are being built with mass timber.  

Understanding all updates reflected in each new edition of the IBC, and how to engage in and influence change in future codes, can be intimidating for professionals in construction and building design. There are several ways the building design community can be involved in the process. 

First and foremost, builders should familiarize themselves with current building code requirements and design guides. Having a clear understanding of the current landscape can help inform you on how to engage in both the model building code development process as well as the code-change processes put in place by individual states. 

2015 International Building Code 

The IBC is in use in 50 states, the District of Columbia, Guam, Northern Marianas Islands, the U.S. Virgin Islands and Puerto Rico. In June 2014, the 2015 version of the IBC was released – and will be adopted by increasingly more jurisdictions over the next few years. Specific to wood buildings, one primary change to the 2015 IBC was the introduction of mass timber, specifically referenced as cross-laminated timber (CLT), for use as Type IV – heavy timber – construction. Other changes for wood construction are reflected in the following standards, which are specified for use in the IBC: 

    •National Design Specification (NDS) for Wood Construction – The 2015 NDS is a dual format allowable stress design and load and resistance factor design standard used to design wood structures worldwide. In this edition, provisions for CLT were added, including the design of CLT members, connections in CLT and fire design of CLT. Another significant change is new provisions that explicitly permit structural composite lumber to be designed for fire requirements using NDS Chapter 16. The 2015 NDS Supplement, packaged with the NDS, contains updated design values for the visually-graded southern pine and the mixed southern pine dimension lumber. 
    •Special Design Provisions for Wind and Seismic (SDPWS) – Provisions have been added to the 2015 SDPWS for seismic design of cantilevered wood-frame diaphragms that provide important design clarifications, especially for design of “corridor-only” multi-story wood-frame structures. There also are revisions to the protocol for determining equivalent deformation-based shear distributions that allow more efficient seismic design of shear walls containing high aspect ratio shear walls. 
    •Wood-Frame Construction Manual for One- and Two-Family Dwellings (WFCM) – New tabulated spans in the 2015 WFCM for lumber framing members reflect changes to design values referenced in the 2015 NDS. Tables also were added to provide prescriptive wood-frame solutions for rafters and ceiling joists in response to the new deflection limits adopted in ICC’s 2015 International Residential Code (IRC) for ceilings using gypsum wallboard or brittle finishes. 
    •Permanent Wood Foundation (PWF) Design Specification – A permanent wood foundation is a load-bearing wood-frame wall system designed for both above and below-grade use as a foundation for light-frame construction. This specification primarily addresses structural design requirements and the 2015 PWF standard has been updated to reflect reference to the 2015 NDS and 2015 SDPWS. 

These new standards equip users with engineered design methods that result in buildings better able to withstand damage and increase longevity. Recently updated design tools are even more relevant for designers hoping to achieve this higher level of performance.

Environmental Benefits Affect Change 

While it is encouraging to see new building systems and materials such as CLT starting to be embraced in the 2015 IBC, proposals are already underway to expand options for wood design in future codes. Currently, the ICC is accepting public comments on code change proposals to be incorporated in the 2018 IBC, and building code officials are already reviewing recommendations from the American Wood Council (AWC). 

Notably, two proposals submitted by AWC would allow up to nine stories of mass-timber construction up to 100-feet tall. Currently, the building code only permits up to five stories for residential structures and six stories of heavy-timber for certain types of commercial structures.  The primary drivers encouraging these changes include the potential environmental benefits that can be realized through wood construction. 

Increased use of wood in building construction has the potential to significantly reduce the environmental impact of the construction industry. 

Illustrated by life-cycle assessment (LCA) studies, wood performs better in terms of embodied energy, air and water pollution, and importantly emissions that contribute to greenhouse gas build-up. Like the trees from which they are derived, wood buildings extend that carbon sink that has removed carbon dioxide from the atmosphere and stored it as carbon in every wood product. 

The green building movement has embraced the inherent benefits of wood through more urban projects, as showcased by the number of tall mass timber buildings being constructed globally. To encourage similar progress in the United States, building codes need to be updated to allow for expanded applications. 

For the proposals mentioned earlier to be adopted in the 2018 IBC, two-thirds of the ICC membership must vote in favor. Building designers have the opportunity to participate in the discussion process by submitting public comments to the ICC and participating in hearings. 

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