Yes. Atlas requires the use of felt underlayment with all our shingle product applications. Felt provides several functions. Although not water proof, felt is water resistant and acts as a secondary protection against wind driven rain. Felt also protects the shingles from resins from roof decking materials, and felt is a required component in meeting Class A or Class C fire ratings. The only alternative to felt underlayment is to use a higher end synthetic underlayment such as Atlas Summit™ Synthetic.