The side of roofing felt that goes down is the smooth side, which faces toward your roof deck. The bumpy or textured side faces up, where it grabs nails and holds shingles in place. Think of it like a sandwich: the smooth side sticks to the wood, and the rough side holds the shingles on top. Getting this right matters because it keeps water out and shingles from sliding off.
Why Does Roofing Felt Direction Matter?
Roofing felt is also called underlayment. It sits between your roof deck and your shingles. The smooth side down stops water from backing up under your shingles.
The bumpy side up gives nails something to grip. This keeps your shingles from moving around in wind or storms.
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What Happens If You Put Felt the Wrong Way?
If the bumpy side goes down, water can sit on the smooth top surface. Water rolls off instead of being caught and drained away. This causes leaks inside your home.
Shingles also slide more easily on a smooth surface. High winds can tear them off. According to industry data, storm damage causes 33 percent of roof replacements nationwide. Proper underlayment helps stop this.
How to Install Felt Correctly
Start at the bottom of your roof. Lay the felt with the smooth side down on the wood deck. Roll it out going up the slope. The bumpy side should face up.
Overlap each row by four inches. Use roofing nails every 12 inches. According to RubyHome, roof installation costs range from 4 to 40 dollars per square foot depending on materials. Good underlayment saves money by preventing leaks that cost much more to fix later.
| Felt Type | Lifespan | Cost |
|---|---|---|
| 15-pound felt | 5 to 10 years | Budget option |
| 30-pound felt | 10 to 15 years | Mid-range |
| Synthetic underlayment | 20 to 30 years | Premium choice |
Why Quality Underlayment Matters Now
According to the Insurance Information Institute, hail damage cost U.S. homeowners 160 billion dollars in reconstruction value in 2024. Good underlayment protects your roof deck from hail and rain. Asphalt shingles, which cover about 80 percent of U.S. homes, need strong support underneath to last their full lifespan of 20 to 30 years.
Average roof replacement costs about 9,526 dollars, according to RubyHome. Catching water damage early with proper felt installation can save thousands. The smooth side goes down. The bumpy side goes up. That simple choice protects your home.
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Connect with an experienced roofing contractor to discuss your roofing needs and schedule an inspection.