A.There are hundreds, if not thousands, of individual code interpretations in this country. A community adopts a code or some version of a model code and enforces it locally. Until recently there were three model codes that were used to develop local codes. However, in 2002, the three code-writing bodies, BOCA, ICBO, and SBCCI, consolidated all operations under one organization called the International Code Council. The ICC's International Residential Code for One- and Two-Family Dwellings (IRC) is catching hold and has currently been adopted by Washington, D.C. and 18 states as a statewide code. This is nice, but if you live in one of the other 32 states, your local code may still use and enforce some other code, like the 1999 BOCA National Building Code, for example. So you'll need to check your local code for a definitive answer.
From a technical standpoint, you should absolutely use felt or housewrap. But from a legal standpoint, you probably don't have to in most cases. The 2003 IRC deals with this in section R703.2, "Weather Resistant Sheathing Paper." It states that asphalt-saturated felt or other approved weather-resistant material shall be applied over...
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