The roof underlayment is actually a layer placed between the sheathing and shingles. It’s an extra humidity barrier that shields your roof decking from drinking water that can be put beneath the shingles. The underlayment is available in the a few styles mentioned down below: Also, take a look at https://www.homerentla.com/top-7-roofing-companies-in-illinois-reliable-choices-for-quality-service/