See Tables 1 and 2 for visually graded lumber species and lumber species combinations and assigned specific gravity per the National Design Specification (NDS) for Wood Construction. Assigned specific gravity in the NDS is an average property based on weight and volume when oven-dry. Bold entries are commonly available lumber species combinations used in International Residential Code and International Building Code span tables for joists and rafters.

1. For a complete listing of lumber species, lumber species combinations and assigned specific gravity, see NDS Supplement Chapter 4 (https://awc.org/pdf-viewer/?idp=4126&idf=4) and its Addendum/Errata (https://awc.org/wp-content/uploads/2021/12/AWC-2018NDS-Supplement-Updates-Errata_22-4-18.pdf).
2. Lumber with specific gravity less than 0.42 may be associated with special prescriptive fastening requirements in accordance with the International Residential Code (IRC) and International Building Code (IBC). Bold entries are commonly available lumber species combinations used in IRC and IBC span tables for joists and rafters.

1. For a complete listing of lumber species, lumber species combinations and assigned specific gravity, see NDS Supplement Chapter 4 (https://awc.org/publications/2018-nds-supplement) and its Addendum/Errata (https://awc.org/publications/2018-nds-updates-errata).
2. Lumber with specific gravity less than 0.42 may be associated with special prescriptive fastening requirements in accordance with the International Residential Code (IRC) and International Building Code (IBC).