Roof Underlayment: Synthetic vs Felt

Roof underlayment is the layer that goes on the roof deck before the shingles or metal panels. You never see it once the roof is done. It is still one of the most important parts of the roof, because it is the backup layer if wind-driven rain gets under a shingle.

What underlayment does

• Sheds water that gets past the roof covering.
• Keeps the deck dry during the install, between tear-off and shingles.
• Gives the shingles or panels a smooth, even surface to sit on.

Felt underlayment

Felt, often called tar paper, is the older option. It is paper or fiberglass mat soaked in asphalt. It works, but it is heavier, it can tear when walked on, and it can wrinkle if it gets wet before the shingles go down.

Synthetic underlayment

Synthetic underlayment is a woven or spun plastic sheet. It is lighter, stronger and harder to tear. It lies flat, gives the crew better footing, and stands up better to sun and rain if a storm rolls in mid-job. That is why we use synthetic underlayment on every package.

Underlayment is not the same as ice and water shield

Ice and water shield is a self-sealing membrane that sticks to the deck. It goes in the places most likely to leak, like valleys and around pipes, and seals around the nails that pass through it. Underlayment covers the rest of the roof. Read more in our guide to ice and water shield on an Arkansas roof.

Underlayment in each Patriot roof package

• Armor and Guardian: premium synthetic underlayment.
• Defender and Shield: synthetic underlayment.

On our Atlas shingle systems, the Atlas Signature Select system warranty requires Atlas underlayment along with the qualifying shingle and other Atlas accessories. Compare the packages on our roof replacement page.

Frequently asked questions

Can underlayment be replaced without a new roof?

Not across the whole roof. The shingles sit on top of it. In a small area, a repair can lift the shingles, replace what is underneath and re-lay them.

Does underlayment stop a leak by itself?

It is a backup, not a roof. Missing or damaged shingles still need to be fixed quickly.

Want a second set of eyes on your roof?

Book a free 30-minute storm or replacement inspection. You get our 21-Point Roof Inspection Report with photos, so you can see your own roof and decide for yourself.