Why are There Dark Spots on My Attic Decking? Roof decking is an important part of your roof, and therefore for your whole home. It is going to basically be the wooden foundation for the entire roof and if there is some reason that the water will get to this decking, it can create some serious problems. This can include problems like structural damage, mold, and mildew to name a few. This is why you need to have a good roof that is not old...