The most current edition is the 2012 IECC.  The 2012 IECC requires duct testing (if ducts and/or air handlers are located in unconditioned space) as well as air tightness testing (blower door).  This marks a significant leap for energy efficient homes-- for the first time ever, a home built in a state or municipality that has adopted the 2012 IECC shall be required to pass testing provided by a 3rd party (HERS Rater).

Regardless of what edition (2006, 2009, 2012) of the IECC your design is subject to, you will need to comply with one of two ways:

This method requires the design to meet or exceed the standards for each design element.  For example, if you have a homeowner who wishes to install aesthetically pleasant yet slightly inefficient windows-- they will not comply with the Prescriptive Path.  See table below for 2012 IECC Prescriptive Path requirements:

This method allows trade-offs within building materials to create an overall building as efficient as the Prescriptive Path.  Using the example above, the homeowner may be able to install their preferred windows so long as they (example) improve the amount of attic insulation to offset the additional energy consumption of the inefficient windows.

The Performance Path (R405) is ideal because it allows builders and architects to achieve the desired energy efficiency standards while using a wider array of building materials, some which may be more financially lucrative or fit the design of the building better.

For these reasons, we encourage our clients to qualify for IECC compliance using the Performance Path in almost all circumstances.