Not every new roof needs an underlayment to keep out the rain. It depends on where you live and how much rain you get each year. Cities like Mobile, AL, Tallahassee, FL, or Lake Charles, LA, get over 50 days and 50 inches of rain annually. Underlayments aren't costly extras, so for residents of those cities, the outlay pays quickly for itself. If you live in a dry place and get less than six inches of rain a year, though, you've got a choice whether an underlayment would benefit your home or not.
What an underlayment? It's a moisture barrier between your roof deck and shingles that helps keep the rain from soaking through your roof deck into your home or business. There are three basic types.
Asphalt felt
Asphalt felt is also known as asphalt saturated felt. If you see it, you'll recognize it since it looks like tar paper, although it is chemically a bit different. If you've lost shingles in a storm, you can see the black underlay where the shingle used to be. It's been around for decades and isn't as hardy as its synthetic counterparts. Asphalt felt fell out of favor about 15 years ago when synthetic underlays became the go-to for roofing pros due to its overall cost-efficiency and ease of use. Asphalt felt is still less expensive than synthetic underlays and is water-resistant.
Rubberized asphalt
Because it uses higher amounts of asphalt and rubber polymers, rubberized asphalt is the most expensive underlay and is waterproof. It will keep your roof deck soak-free even if you lose a bunch of shingles during a storm or during an extended rain event.
Non-bitumen synthetic
Synthetic underlays like non-bitumen weigh less and cover more of your roof deck than non-synthetics like asphalt felt. They are water-resistant. A non-bitumen underlay is made from polypropylene or polyethylene, the same materials that you'll find in much of your kitchen plastic.
Is a waterproof or water-resistant underlay best?
It depends on where you live. Do you know the difference between a water-resistant and waterproof underlay? Waterproof underlays won't allow any water to permeate your roof deck. You can't guarantee that with water-resistant underlays. They resist water, but you could still have some leakage over the life of your roof.
If you live in a rainy climate, chances are high that your roofing contractors will quote your repair or roof replacement with the waterproof underlay unless you specify that you want a water-resistant one.
To learn more, contact a resource like Indy Roof Company.
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