If you are working within the NYSERDA program it is important to do the calculations for an attic to vault conversion differently than normal due to a limitation in the way their software reads our HPXML files:

On the input screen, choose to add a vaulted ceiling. If there was an attic chosen, click on the trash can icon to remove it. Choose the appropriate insulation method that most closely resembles the current attic floor insulation.

Next click on the Now and Goal button for the Vault under Related Measures in the right hand Context Pane.

Next, double check that the square footage for the BASE Modeled Area. Make sure that this is the same as the footprint of the attic floor that is being converted. Next, set the IMPROVED Modeled Area to be the total square footage of the new vaulted ceiling. It should be a larger number based on the roof pitch. For an easy multiplier for the roof pitch, go here.

Then, double check the BASE Cavity Insulation and determine if the R Value looks right for the existing attic floor insulation (if any). Next, set the IMPROVED Cavity Insulation to the R-value of the material you wil be installing between the ceiling rafters. If you are overspraying any insulation on the top of the rafters, then for that portion above the rafters, you can add a value in the IMPROVED Continuous Insulation field.