Interpretation #9475

FBC Building 1507.1.1.1 and Residential 905.1.1 Underlayment has 3 options. Option 2 is for taped joints and refers you to Table 1507.1,1.1 where either a single layer of underlayment is required at a "Roof Slope 4:12 and Greater" or 2 layers at "Roof Slope 2:12 and Less Than 4:12". Zip system has had their system approved without it in some jurisdictions using product approval that Zip feels supersedes code. The minimum standards of the Code are not intended to be lessened by product approval. These same requirements are in the Existing Building subcodes. In Existing Section 706.7 Mitigation and more specifically 706.7.2 "Roof secondary water barrier for existing structures with wood roof decks" and refers back to the Building and Residential sections cited above. The intent is that these underlayments serve as secondary water barriers if the primary roof covering is compromised. The Codes prescriptive underlayment requirements are based on testing as secondary water barriers. Zip systems are not described as an option to achieve this requirement.