This comprehensive code comprises all building, plumbing, mechanical, fuel gas and electrical requirements for one- and two-family dwellings and townhouses up to three stories. The 2021 IRC contains many important changes such as: Braced wall lines must be placed on a physical wall or placed between multiple walls. The rated separation for two-family dwellings is 1 hour whether or not a lot line exists between units. Emergency escape and rescue openings require a clear 36-inch-wide path to a public way. An engineered design is required for storm shelters. A habitable attic is limited to one-half the area of the story below and the dwelling requires sprinklers. Updated Wind Speed maps match IBC and ASCE 7 maps.