Which material is recommended as an underlayment for roofing applications?

The recommendation of 30 lb roofing felt as an underlayment for roofing applications stems from its effective properties for moisture barrier and protection. Roofing felt, specifically the heavier 30 lb variety, provides a robust barrier against water infiltration while allowing for breathability, which is important in preventing moisture buildup and potential roof damage over time. This material is designed to be durable and withstand various weather conditions, making it an ideal choice for protecting the roof deck before installing the final roofing materials. Its weight and thickness also contribute to its ability to resist tearing, an essential quality given the installation process, which may involve walking on the felt.

In contrast, plywood is typically used as a substrate or sheathing for a roof but does not serve the same purpose as an underlayment. Fiberglass, while it has uses in various construction applications, is not commonly used as a roofing underlayment; it lacks the necessary properties for a moisture barrier. Plastic sheeting does not provide the same level of protection as roofing felt; it's more suitable for vapor barriers or ground covers rather than as an integral component in roofing assemblies.