Georgia Roof Guide

What is roof underlayment?

Short answer. Roof underlayment is a water-resistant sheet, usually synthetic or asphalt felt, rolled over the roof deck before the shingles go on. It sits between the wood and the shingles as a second line of defense, catching water that gets past the shingles and protecting the deck when shingles blow off.

Where it sits in the stack

  1. Rafters or trusses
  2. Decking (plywood or OSB)
  3. Drip edge at the eaves
  4. Self-adhered membrane in valleys, around penetrations and on low-slope sections
  5. Underlayment over the rest of the deck
  6. Drip edge at the rakes, then starter strip and shingles

What you will see in an estimate

Estimates list underlayment by type: "felt #15," "felt #30," "synthetic underlayment," and "ice and water barrier" or "self-adhered membrane" for the specialty areas. Insurance estimates price it by the square, meaning per 100 square feet of roof. If an estimate shows felt only and no membrane in the valleys, ask why.

Why Georgia homeowners should care

When a thunderstorm peels off a section of shingles, the underlayment is the only thing between the rain and your ceiling. Well-fastened synthetic underlayment holds up far better in wind than felt. It also keeps the deck dry if a pop-up afternoon storm arrives partway through a replacement.

How to tell what you have

From the attic you see only the underside of the deck. The underlayment is visible from outside only at a damaged spot or at an edge during a repair. Older roofs mostly have felt, newer ones mostly synthetic. For more, read synthetic underlayment vs felt and roof anatomy explained.

In depth

Are impact-resistant (Class 4) shingles worth it in Georgia?What UL 2218 Class 4 really tests, what it does not promise, how Georgia's FORTIFIED discount law works, and wWhat is drip edge, and does a Georgia roof need it?What roof drip edge does, what IRC R905.2.8.5 requires in Georgia, how it should lap with underlayment, and hoOSB or plywood roof decking: which is better, and what happens at a reroof?OSB vs plywood roof decking in Georgia: span ratings and thickness, how each fails when wet, plank decks, and

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