Roof decking, or sheathing, is the first layer of roofing that supports the underlayment and shingles. For flat roofs, you should consider using a more water-resistant material, while slanted roofs have the benefit of not letting water pool at the top of your home.
The two most common materials for roof decking are plywood and OSB, also known as composite plywood. Plywood is considered a more expensive option but offers greater insulation and protection from the elements. Composite plywood does offer some water resistance and is the go-to option for most roofs.
Although the underlayment isn’t always necessary for some homes, you don’t want to be caught without it when bad weather hits. You can find underlayment in materials like asphalt-saturated felt, rubberized asphalt, and synthetic underlayment.
Rubberized asphalt is considered the best option for waterproofing your roof but is also one of the most costly. The next best option for protection and cost is synthetic underlayment, currently the most popular choice for roofing today.