The roof decking could be the layer of plywood or O.S.B. nailed towards the trusses or rafters. Roof decking is usually 7/sixteen” and comes in 4’x8’ sheets. In case you’re tearing off old roofing, the roofer can search for problems that needs to be repaired when the deck is bare. https://digitalbizgenius.com/top-5-roofing-contractors-for-joliet-il-expert-services-for-your-home/