J Quintero Roofing - When should I use 30lb felt? Most standard pitched roofs only need a 15lb. felt for proper underlayment. 30lb. is used for many specialty applications such as: low
Choosing Roofing Underlayment - Fine Homebuilding
Why Synthetic Felt Performs Better than 15 lb Felt
Synthetic Underlayment: A Roofing Professional's Guide