Why Roof Underlayment Is Crucial to a Complete Roof System
Don’t let shady roofers intimidate you with their secret language. We get it. I mean, what is underlayment, anyway? Good news! You don’t have to get up on a ladder or hammer any shingles to understand the different parts of your roof—and why they are important.
At Roofing Louisiana, we provide a Red Carpet Experience for all our clients, and that means we don’t cut corners while we work or communicate. If you want to know why we replace every part of your roof system–from sheathing to flashing to, yes, underlayment–we happy to share why. So…
What is Underlayment?
Roof underlayment is the water-resistant or waterproof barrier that’s installed between your roof decking and your shingles. It’s your roof’s second line of defense. Of course, you have shingles to protect your home when rain, wind, or debris, but what is underlayment? It’s the backup, if anything gets past your shingles.
There are a few types of underlayment:
- Felt (Asphalt-Saturated): This is the traditional black paper-like material that’s been used for decades.
- Synthetic Underlayment: Modern and more durable, synthetic options offer better protection and resistance to tearing.
- Peel-and-Stick (Self-Adhering): Especially useful around vulnerable areas like valleys and eaves, this waterproof material sticks directly to the decking for maximum seal.
No matter the material, the job of the underlayment is the same—keep moisture out and protect the wood decking beneath.
Why Replacing Underlayment Matters
Here’s the thing: roofing is a system, and every layer has to work together. If you’re replacing your roof, skipping the underlayment or leaving the old one in place is a risky move. Now you know what is underlayment, here’s why it’s important:
1. It’s Your Backup Protection Against Leaks
Even the best shingles can fail in a heavy Louisiana storm. Wind can lift them. Hail can crack them. Water can find its way in. But your underlayment is your safety net. It catches the leaks before they become major damage.
2. It Can Be Damaged or Deteriorated
Underlayment breaks down over time. Moisture, heat, and age can make it brittle, torn, or moldy. Reinstalling new shingles over old underlayment just doesn’t work. Even if it’s not that old, there are 40,000 nails on an average roof, which means 40,000 holes in the old underlayment. That old Swiss cheese can’t do much protecting.
3. It Affects Warranty Coverage
Most major roofing manufacturers require new, properly installed underlayment to honor their warranties. If a contractor tries to save money by leaving the old stuff, they might be saving on cost—but risking your coverage.
4. It Keeps Your Decking Dry
Your decking is the wooden foundation of your roof. Once it gets wet, that’s bad news, especially down in South Louisiana. Once your decking gets wet it can warp, rot, or grow mold in no time. Good underlayment ensures that your decking stays dry—and your entire roof system stays structurally sound.
How Underlayment Fits into a Complete Roof System
REMEMBER—a roof isn’t just a layer of shingles. It’s a full system of parts working together:
- Decking or Roof Sheathing
- Underlayment
- Shingles
- Drip Edge
- Flashing
- Ventilation
Each layer plays a role. Skip one, and you compromise them all.
At Roofing Louisiana, we don’t believe in cutting corners. We tear down to the decking to inspect and replace your underlayment as needed. We only use high-quality materials that are designed to stand up to Louisiana’s extreme weather. And we follow manufacturer guidelines to protect your warranty and your home.
Don’t Be Fooled by a Cheap Quote
Let’s be real—some contractors will skip the underlayment step or reuse what’s already there to give you a lower price. But here’s what they’re not telling you: that shortcut can cost you thousands in future repairs. And they definitely won’t be around when your roof starts leaking in a storm and the manufacturer denies your warranty.
A complete roof system might cost a little more upfront, but it pays for itself in performance, durability, and peace of mind.
Final Thoughts
If you’re replacing your roof, don’t just ask about shingles. Don’t wonder what is underlayment anyway. Ask if the underlayment will be changed. The difference between a roof that looks good and a roof that lasts comes down to what’s under the surface.
Underlayment is your silent shield—and without it, your roof is vulnerable. At Roofing Louisiana, we’re committed to doing it right the first time. We install complete roof systems, and after decades of dedication to Acadiana, you know we’re not leaving town.
Ready to protect your home with a roof that’s built to last? Schedule your free inspection today, and let’s make sure every layer—including your underlayment—is ready for whatever the harsh South Louisiana weather throws at it.
