Roof Underlayment: What Florida Homeowners Should Know

Roof underlayment is the water barrier that sits between your roof deck and your shingles, metal, or tile. It's your backup plan. If wind tears off shingles or water sneaks under tile, the underlayment is what keeps rain out of your attic.

Most homeowners never see it. But in Florida, where storms push rain sideways, it does a lot of quiet work. Here's what it is, the main types, and what to ask your roofer about it.

What Roof Underlayment Does

Think of your roof in layers. From the bottom up, you've got:

• Rafters or trusses. The frame of the roof.
• Roof deck. Usually plywood or OSB boards nailed to the frame.
• Underlayment. A sheet or membrane rolled out over the deck.
• Roof covering. Shingles, metal, or tile on top.

The roof covering is your first line of defense. The underlayment is your second. It catches water that gets past the top layer and sends it down and off the roof. It also protects the wood deck from moisture.

When a storm rips shingles off, the underlayment is often the only thing between the rain and your ceiling. A good one can buy you time until a roofer can make repairs.

The Main Types of Underlayment

Felt (Tar Paper)

Felt has been around for a long time. It's paper or fiberglass soaked in asphalt. It's cheap and it works, but it has downsides. It can tear in high wind, it soaks up moisture, and it breaks down faster in heat. Fewer roofers use it as the main layer today.

Synthetic Underlayment

Synthetic is made from woven or spun plastic. It's lighter and stronger than felt. It resists tearing, it doesn't soak up water, and it holds up better if it sits in the sun for a few days during a job. It's now one of the most common choices for shingle and metal roofs.

Self Adhered (Peel and Stick) Membrane

This type has a sticky back. You peel off the film and press it right onto the roof deck. It seals around nails and bonds to the wood. That makes it very good at keeping out wind driven rain. It costs more than felt or synthetic, but many Florida roofers use it, at least in the spots most likely to leak, like valleys and edges.

Why Underlayment Matters More in Florida

Florida gets heavy rain, strong wind, and long hot summers. That's tough on every layer of a roof.

When a tropical storm or hurricane blows through, wind can lift shingles or tiles. Rain then hits the underlayment directly. If that layer is weak, torn, or poorly sealed, water goes straight into the deck and the attic.

Florida law takes this seriously. State law directs the Florida Building Code to include standards for secondary water barriers on roofs. It also calls for a roof replacement on many older homes to include a secondary water barrier and better roof deck attachment. In plain English: when you replace the roof on an older Florida home, the new roof should do a better job of keeping water out than the old one did.

A licensed roofer should know what the current code requires for your home and pull the permit for the job.

Underlayment Under Tile Roofs

This one surprises a lot of people. On a tile roof, the tiles are mostly there to shed water and protect what's below. The underlayment does much of the actual waterproofing.

Concrete and clay tiles can last for decades. The underlayment under them usually doesn't. It often needs to be replaced every 15 to 20 years, even if the tiles still look fine. When an older tile roof starts to leak, worn out underlayment is one of the first things we check.

The good news is that tiles can sometimes be lifted and reused while the underlayment below them is replaced. Whether that works depends on the condition of the tiles.

Signs Your Underlayment May Be Failing

You usually can't see underlayment from the ground. But these clues can point to a problem:

• Water stains on your ceiling, even when the roof looks fine from outside
• Damp spots or dark stains on the wood in your attic
• Leaks that show up only during heavy, wind driven rain
• An older tile roof that has started to leak in more than one spot
• Shingles that are missing, which leaves the underlayment exposed to sun and rain

If you spot any of these, don't wait. Small leaks turn into rotted decking and mold faster than you'd think in Florida's humidity. Our roof repair team can track down the source.

Questions to Ask Your Roofer About Underlayment

When you get quotes for a new roof, underlayment is one area where cheap bids often cut corners. Ask these questions:

• What type of underlayment will you use? Felt, synthetic, self adhered, or a mix?
• Will it cover the whole deck or just certain areas?
• How will it be fastened or sealed?
• Does your plan meet the current Florida Building Code for my home?
• Will you pull the permit?
• What happens if you find rotted decking? Get the answer in writing.

A good roofer will answer these without any fuss. If someone can't tell you what goes under your shingles, that's a red flag.

Quick FAQ

Can you replace underlayment without replacing the whole roof?

On shingle and metal roofs, the underlayment is almost always replaced when the roof is replaced. Swapping it alone means taking the top layer off anyway. On tile roofs, it's sometimes possible to lift and reuse the tiles while new underlayment goes down.

Does underlayment affect my insurance?

It can. Florida law requires home insurers to offer discounts for features that help a home resist wind, including how well the roof covering performs. Ask your agent what your policy offers.

Is underlayment included in a roof replacement quote?

It should be. Make sure your quote names the product so you can compare bids fairly. Learn more about our roof replacement process.

Book a Roof Inspection

Not sure what's under your roof or how it's holding up? Don Schmidt Roofing has been helping homeowners in St. Cloud, Kissimmee, Orlando, and Osceola County since 1988. We're family owned, A+ rated with the BBB, licensed and insured, and an Owens Corning Preferred Contractor.

Book a roof inspection or call (407) 892-9884. We'll tell you straight what we find.