I have been receiving questions from roofers about the uplift requirements for underlayments under tile in the HVHZ zones. It is my understanding that for Non-HVHZ, the FRSA/TRI manual and R301.2.1.3 is used to determine the wind uplift requirement, which is then compared to the underlayment manufacturer's published FBC Non-HVHZ approvals to find an assembly that meets the uplift pressures. However, the M-D NOAs and FBC HVHZ approvals do not publish uplift pressures with their assembly approvals. This is because the weakest link is in the required nailed 30#. The FBC Sections 1518.2, 1518.3 and 1518.4 indicate requirements for 30# securement, but do not indicate what uplift pressure the specified fastening achieves, and doesn't indicate if it needs to be extrapolated at the ridges and perimeters/corners. Therefore, it seems that a roof system will be installed to code with any approved system (as listed in the NOAs of FBC HVHZ approvals) under tile as long as the 30# is nailed in accordance with FBC Sections 1518.2, 1518.3 and 1518.4, despite not having an uplift pressure rating. Please confirm. If this is not the case, please indicate how to determine the allowable uplift pressure of a system with an NOA since the NOAs do not list MDPs for underlayments. Thank you!