How do I choose a roof underlayment?
A majority of underlayment product offer about the same amount of protection against smoke, but flame protection may vary significantly. Look for a rating of A, B, C. An A rating is the best (this is the most fire-resistant options) and C is the worst (offers the least fire-resistance).
Synthetic Underlayment This is currently the most popular choice for roof underlayment, and with good reason. Made with an asphalt-saturated basemat and fortified with a mix of fiberglass, this product is not only extremely water-resistant, much stronger and more resistant to tears than other types of underlayment.