A few things to consider about this sereis of code changes to the 2009 IRC:
A) The IRC now contains prescriptive requirements for the design of dwelling fire sprinkler systems. These requirements will be correlated to the next edition of NFPA 13D. This prescriptive design allows for cookbook style calculations for the design and plan review of these systems.
B) Based on a series of code changes, the 2009 IRC will require a dwelling fire sprinkler system in all townhouses effective the date the code is adopted. The requirements for one- and two-family dwellings are effective January 1, 2011. The idea behind this is analagous to certain changes in NFPA standards over the years. By having an effective date, it allows the regulated community and regulators to become prepared for its implementation.
C) With the adoption of IRC Section P2904, the building official (rather than the fire official) is responsible for the plan review and inspection of dwelling fire sprinkler systems. However, this will vary based on each jurisdiction.
D) The fire-resistance rating of the party wall between townhomes is reduced from 2-hour to 1-hour based on the installation of the dwelling fire sprinkler system.
Let me know if you have any questions.