Which standard is acceptable for underlayment for asphalt shingle covering with an ultimate design wind of 140 mph?

The standard ASTM D226 Type II is indeed a suitable choice for underlayment when using asphalt shingles in areas with high wind design pressures, such as those reaching up to 140 mph. This standard specifies the requirements for water-resistant underlayment used in roofing applications, particularly designed for steep-slope roofing.

ASTM D226 Type II underlayment is made from felt and is classified as a high-quality, durable product that is appropriate for use under asphalt shingles, providing a secondary line of defense against water intrusion. The robust properties of this underlayment help resist damage from high winds and protect the roofing system, ensuring integrity and performance under challenging conditions.

Other standards such as ASTM D4869 Type III, ASTM D6757, and ASTM D4819 may also relate to underlayment for roofing applications; however, they do not provide the same level of performance or suitability specific to the required ultimate design wind speed of 140 mph that ASTM D226 Type II ensures. Each of these other standards has particular intended uses and may not be rated to withstand the same wind forces as specified for ASTM D226 Type II, making the latter the best option in this scenario.