In order to obtain a building permit for a deck attached to a single family residential home, your plans must be reviewed to be in compliance with the IRC. The International Residential Code (IRC) is a comprehensive collection of the specific rules that apply to residential construction and that is administered by the International Code Council (ICC). If you are a contractor, this book is a must have. You can buy a copy online at www.iccsafe.org. 

Nearly all states in the US have at some level adopted the International Residential Code as the model building code for construction of one- and two-family dwellings (duplexes), as well as townhomes. Townhomes are unique multi-family structures with an unlimited number of connected dwelling units. However, the units must be separated from the foundation vertically to the roof; no part of any one can be under or on top of another. Each unit must also be open on at least two sides. Traditional row homes are an example of townhome construction under the IRC.

In regions that have not adopted the IRC, they likely use the group R-3 exceptions contained in the International Building Code. These exceptions generally modify the commercial rules to be very similar to the IRC. Building codes are not regulated at the federal government level, and they are the authority of the state.

The building inspector’s job is to interpret and enforce the rules as they are stated in the IRC. In other words, inspectors are not allowed to make their own rules. Because of this, building codes should be fairly consistent from city to city and state to state.