STORM GUARD by GAF:

Ice and Water Shield: Simply the best secondary resource for all those complicated areas of your roof. See:

15lb or 30lb felt ? In order to achieve fire-resistant ratings (Class A or C), an under-layments must be used regardless of the type of shingle being installed. A minimum of 2 layers of felt or 60lbs of base (2 layers of 30lb) is required for roofs with slopes less than 4/12. In such cases, the application must meet the requirements for low slope roofs. Alternatives for 2 layers would be 1 layer ice and water shield. The difference between 15lb and 30lb : We prefer the heavier felt for a few reasons.  We prefer to provide a more durable temporary water barrier while in renovations.  The 30 lb felt wont tear out while walking on steep roofs.  The felt paper lays evenly reducing wrinkles in the roof system.

NO. 30 ASTM -- Features a premium quality TAMKO organic felt that is saturated with asphalt. Accepted for use as an underlayment felt to be applied over the deck prior to the installation of TAMKO asphalt shingles. ASTM D-226, Type II. 72'x36" 216 sq. ft. per roll

30LB PLAIN FELT 2SQ/RL Other felt products by Tamko Tile and Metal Under layments and or Ice and Water shield Same product different names but same effect, overall the best secondary solution for high water areas, flashing details and roof penetrations. As seen in the photo below. Ice and Water Shield can add added protection to the life cycle of the roof. Also can and should be used for low sloped shingle or metal roofs.

A GAF 5 STEP TO A SUCCESSFUL ENERGY EFFICIENT WATER TIGHT ROOF