Underlayment is a felt (15 lb or 30 lb) or synthetic material installed over your decking to provide additional protection if water gets underneath the roofing materials. It's one of the most crucial components of a roof system.
In this video, you'll learn what roof underlayment it is, why it's necessary, the different types,, and more.
After watching this video, don't forget to check out the next video on the roofing components: Drip Edge.