A building official must enforce the code; his opinion would only apply to areas where the code is not clear.

To determine what the code says you must tell us what code applies in your area.

Asphalt shingle roofing requirements in building codes have closely followed the recommendations of the NRCA (National Roofing Contractors Association) for the past 30 years. The provisions of the 2009 IRC does that so it is a good guide:

"R905.2.2 Slope.
Asphalt shingles shall be used only on roof slopes of 2 units vertical in 12 units horizontal (2:12) or greater. For roof slopes from 2 units vertical in 12 units horizontal (2:12) up to 4 units vertical in 12 units horizontal (4:12), double underlayment application is required in accordance with Section R905.2.7.

R905.2.7 Underlayment application.
For roof slopes from 2 units vertical in 12 units horizontal (17-percent slope), up to 4 units vertical in 12 units horizontal (33-percent slope), underlayment shall be two layers applied in the following manner. Apply a 19-inch (483 mm) strip of underlayment felt parallel to and starting at the eaves, fastened sufficiently to hold in place. Starting at the eave, apply 36-inch-wide (914 mm) sheets of underlayment, overlapping successive sheets 19 inches (483 mm), and fastened sufficiently to hold in place. Distortions in the underlayment shall not interfere with the ability of the shingles to seal.

"Grace Ice & Water Shield" shingle underlayment is recognized by the IRC as a "Self-adhering polymer modified bitumen sheet complying with ASTM D 1970" and it is commonly accepted as a substitute for the double coverage underlayment described above, in fact it is generally considered far superior. If you apply Grace Water Based Primer to the sheathing, it would be virtually impossible to separate the underlayment from the sheathing. I don't recommend using any other brand of this material so include the Grace product in your roofing spec. "without substitution".

If these requirements apply, I can't see how a building inspector could have grounds for objecting to your roofing design unless there is a local code restriction.

Thanks for the response!!!! I will go to the building inspector with this new information and see what he states.

Thanks again