That's what I was saying. You can have a "home business" under the 2009 IRC but as far as egress it must meet 2009 IBC regulations. The classification would change from a R3 to an R2.
Note: If the area is less than 10% of the structure it would still be classified as an R3. Also there is a maximum square footage for the live/work units. 50% of the residential area or 3000 square feet whichever comes first.
Code sections below!
R101.2 Scope. The provisions of the International Residential Code for One- and Two-family Dwellings shall apply to the construction, alteration, movement, enlargement, replacement, repair, equipment, use and occupancy, location, removal and demolition of detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress and their accessory structures.
Exception: Live/work units complying with the requirements of Section 419 of the International Building Code shall be permitted to be built as one- and two-family dwellings or townhouses. Fire suppression required by Section 419.5 of the International Building Code when constructed under the International Residential Code for One- and Two-family Dwellings shall conform to Section 903.3.1.3 of the International Building Code.
SECTION 419 LIVE/WORK UNITS
2009 IBC 419.1 General. A live/work unit is a dwelling unit or sleeping unit in which a significant portion of the space includes a nonresidential use that is operated by the tenant and shall comply with Sections 419.1 through 419.8.
Exception: Dwelling or sleeping units that include an office that is less than 10 percent of the area of the dwelling unit shall not be classified as a live/work unit.
2009 IBC
419.1.1 Limitations. The following shall apply to all live/work areas:
1. The live/work unit is permitted to be a maximum of 3,000 square feet (279 m2);
2. The nonresidential area is permitted to be a maximum 50 percent of the area of each live/work unit;
3. The nonresidential area function shall be limited to the first or main floor only of the live/work unit; and
4. A maximum of five nonresidential workers or employees are allowed to occupy the nonresidential area at any one time.