The recent approval of the 2018 International Building Code (IBC) and International Residential Code (IRC) is of keen interest to professionals in the construction industry as it often means expanded options for structural applications. In support of these two codes, the American Wood Council has developed two standards: the 2018 National Design Specification® (NDS®) for Wood Construction and 2018 Wood Frame Construction Manual (WFCM). Each has been approved by the American National Standards Institute (ANSI) as American National Standards and both are referenced for wood design in the new IBC and IRC.
The 2018 NDS is key to designers of wood buildings and those responsible for oversight and code enforcement, and defines the methods to be followed in structural design with traditional and engineered wood products, as well as the design and fabrication of single and multiple fastener connections. Primary changes in the 2018 NDS include:
- Adjustments to fire design provisions for exposed wood members and connections to aid in new applications where fire resistance ratings are required;
- Added design provisions for fastener head pull-through in lumber and wood structural panels;
- New design provisions for ring shank nails to address increased roof uplift loads in ASCE 7-16;
- Added design provisions for stainless steel nail withdrawal; and,
- Revised provisions for incised lumber.
The 2018 WFCM equips designers and code officials with engineered and prescriptive construction methods that result in more resilient wood buildings that are better able to withstand forces associated with extreme natural disasters. Primary changes in the 2018 WFCM include:
- Clarification of terminology, and minimum construction details and limits of rake overhangs based on increased wind pressures;
- Revision of the “Roof Sheathing Attachment Requirements for Wind Loads” table to give common, box, and RSRS nail size and sheathing options by including requirements for uplift load per nail and fastener uplift capacity;
- Addition of roof rafter uplift tables to provide design wind pressure and maximum spans for roof rafters in accordance with ASCE 7-16 wind pressures;
- Updated design load standard reference from ASCE 7-10 to ASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures;
- Revisions to coordinate with ASCE 7-16’s increased roof wind uplift pressures and addition of lower wind speed categories (i.e. 90, 95, 100, and 105 mph); and
- Incorporation of fastener criteria from the 2018 NDS to include provisions for roof sheathing ring shank (RSRS) nails and fastener head pull through design procedures.
To make this code-referenced standard the most user-friendly it can be, AWC will now be developing supporting publications such as an NDS Commentary, revising technical reports and design aids to be consistent with this new edition, and conducting further research to ensure continued widespread acceptance of wood in construction.
Understanding all of the latest changes and what is allowed in various jurisdictions can also be a daunting prospect. In order to understand what the latest building code and standards updates mean for the specification of traditional and engineered wood products in buildings, AWC has several free webinars scheduled or available on-demand to provide an overview of changes to the 2018 AWC standards and 2018 building codes.
Both publications are currently available in a read-only electronic format on the AWC website, at www.awc.org/codes-standards/publications. A print version of each standard is expected to become available in early 2018.