The roof decking could be the layer of plywood or O.S.B. nailed into the trusses or rafters. Roof decking is often seven/sixteen” and is available in 4’x8’ sheets. When you’re tearing off previous roofing, the roofer can try to look for problems that needs to be fixed once the deck https://digitalbizgenius.com/top-5-roofing-contractors-for-joliet-il-expert-services-for-your-home/