Best Underlayment for a Metal Roof

Choosing the right underlayment is just as important as choosing your metal roof. The material you install beneath the metal panels impacts how well and how long your roof holds up in Florida’s weather. Understanding the available underlayment options will allow you to make the right call for your home.

What Does Roof Underlayment Do?

Roof underlayment blocks moisture, reduces heat buildup, and protects against wind-driven rain. Think of it as the roof’s last line of defense before water reaches your home.

It’s installed directly onto the roof decking before the sheets of metal roofing go on. When done right, underlayment keeps the roofing system watertight and stops condensation from building up underneath. That’s especially important in hot, humid climates like Florida and is a crucial part of any quality roof installation.

Underlayment Material Options for Metal Roofs

There are three types of underlayment used with metal roofing.

1. Felt Underlayment (Asphalt-Saturated Felt)

Felt, also called tar paper, is the oldest underlayment still in use. It’s made by soaking cellulose or fiberglass mats in asphalt. Then it’s rolled out in 15 mil and 30 mil thicknesses. The thicker version offers better durability but still falls short compared to modern materials.

Felt is cost-effective and easy to work with. That’s why it’s still used on budget projects or quick installs. But it doesn’t hold up well under a metal roof in a hot, humid place like Florida.

It tears easily, soaks up water, and breaks down fast under heat. It also wrinkles or shifts under the metal roofing panels, which can lead to leaks.

Pros:

• Cheapest option upfront
• Easy to install and widely available

Cons:

• Not built for Florida’s heat and humidity
• Soaks up moisture, leading to mold or rot
• Wears out in 10 to 15 years, far less than the metal roof above it

2. Synthetic Underlayment

Synthetic underlayment is made from woven plastic fibers, usually polypropylene or polyethylene. It’s designed to stay strong, even in high heat, wind, or heavy rain.

This material doesn’t wrinkle or absorb moisture like felt. It lasts longer, goes on faster, and is safer to walk on during installation. This makes it a solid upgrade, especially in Florida, where the weather is rough on roofs.

Check the specs, though, because some synthetics aren’t rated for the heat that builds up under metal panels. And as with any underlayment material, it needs to be installed correctly in order to work as it should.

Pros:

• Strong and tear-resistant
• Blocks moisture without absorbing it
• Resists fungus, mold, and mildew growth
• Handles Florida’s heat, wind, and humidity
• Lightweight and easy to install
• Textured surface improves safety during the installation process
• Some brands can handle longer UV exposure if the job gets delayed

Cons:

• Costs more than felt
• Not all brands meet high-heat standards for metal roofs
• Not biodegradable

Tip: Expert roofers know how to work around the challenges of synthetic roof underlayment.

3. Self-Adhered Underlayment

Self‑adhered underlayment, also known as peel-and-stick, uses a rubberized asphalt or butyl adhesive layered over a polyethylene sheet. It bonds directly to the roof deck without fasteners, forming a waterproof seal. That seal makes it ideal for high-risk areas like eaves, valleys, and roof penetrations such as vents, chimneys, skylights, HVAC ducts, and solar panel mounts.

The Insurance Institute for Business & Home Safety reports, “A properly installed sealed roof deck can reduce water entry through a compromised roof by as much as 95%.” That added protection makes self-adhered underlayments especially valuable in Florida’s hurricane-prone zones.

In Florida, this type of underlayment is common and often required for coastal and hurricane zones. Furthermore, many insurance companies offer discounts when self-adhered underlayment is installed directly to the deck.

Pros:

• Creates an airtight, waterproof seal
• Meets high wind and hurricane codes when installed directly to the roof sheathing
• Ideal for complex roof lines and vulnerable areas like edges, valleys, and penetrations
• May reduce insurance premiums if applied correctly

Cons:

• Must be applied to a clean, dry deck; wet or dirty surfaces will prevent correct adhesion
• The adhesive degrades quickly when exposed to sunlight, which results in a short UV window in which to work
• Hard to remove during re-roofing and removal can damage the roof deck

Why Underlayment Matters for Metal Panel Roofs

Underlayment stops water from reaching the sheathing, helps manage condensation, and adds protection where metal alone can’t. It’s a key part of your roofing system and should not be skipped.

Metal roofs expand and contract with temperature swings (one of their known challenges). Without the right underlayment, that movement can lead to leaks over time. It also helps reduce noise from rain, keeping your home quieter during storms.

In Florida, roof underlayment plays a big role due to the frequent rain, high humidity, coastal exposure, and hurricanes that put your roof to extreme tests. A strong underlayment is important to protect the insulation and your entire home.

Best Underlayment for Florida’s Climate

Synthetic underlayment is the best choice. It handles Florida’s extreme heat, high humidity, and heavy rain better than other materials. It also resists UV exposure during installation and won’t break down under the heat of metal panels.

Self-adhered underlayment is another strong option, especially for homes in coastal areas or with complex rooflines. It forms a watertight seal directly to the roof deck, which helps prevent leaks from the wind-driven rain that is common during hurricanes.

Felt underlayment is the least reliable in Florida’s climate. It absorbs moisture and deteriorates faster under metal roofing systems due to the heat factor. It may work short-term, but is not built to last in Florida.

Choosing the Right Underlayment

The best underlayment depends on various factors, including your metal roof type, budget, and climate. There’s no one-size-fits-all choice. Consider the following before making your decision.

Roof Slope

Low-slope roofs need extra protection from standing water. Self-adhered or high-performance synthetic works best here. Steeper slopes shed water faster, so high-heat-resistant synthetic is enough.

Climate Conditions

Florida homeowners need to choose something built for heat and moisture. Felt won’t last. Synthetic or self-adhered underlayments are better for holding up under the sun, storms, and salty air.

Metal Roof Type

Standing seam metal roofing systems require high-temperature-rated underlayment. Check your panel manufacturer’s recommendations. The wrong underlayment product could void your warranty or shorten your roof’s lifespan.

Budget

Felt is the cheapest but wears out fast. Synthetic lasts longer and adds better protection, but costs more than felt. Self-adhered offers the strongest seal but costs the most, starting at around $100 per square (100 square feet).

Installation

Felt and synthetic underlayments need fasteners. Self-adhered underlayment sticks on contact and doesn’t leave nail holes, but there’s little room for error. Whatever you choose, correct installation matters because a bad installation will cause leaks, rot, and expensive repairs down the line.

FAQs About Metal Roofing Underlayment

Our clients often ask the following questions.

Does a metal roof really need an underlayment?

Yes, an underlayment is a critical component in any roofing system, even a metal one. It’s vital for moisture control, noise reduction, and long-term roof health.

Does underlayment reduce roof noise?

Yes, underlayment helps dampen noise from rain and wind hitting the metal panels. Thicker, rubberized materials like self-adhered membranes offer the most sound reduction.

What’s the best underlayment for metal roofing in Florida?

Synthetic underlayment is the best option for Florida homes. Self-adhered underlayment adds extra protection for coastal homes or low-slope roofs.

How much does underlayment cost?

Felt is the cheapest at around $20 to $60 per square (100 square feet). High-temp synthetic underlayment ranges from $30 to $70 per square, while self-adhered options cost $100 to $150 per square.

What is the lifespan of underlayment under a metal roof?

Felt lasts 10 to 15 years, depending on its exposure. High-quality synthetic or self-adhered products last 30 years or more when installed correctly.

Can I install the underlayment myself?

Felt and synthetic are easier for DIYers. Self-adhered underlayment requires precision. Once it sticks, it’s hard to adjust. Hiring a licensed roofing contractor will give you the best possible results under your metal roof.

Make the Right Call for Long-Term Roof Protection

The right underlayment plays a major role in how well your metal roof holds up, especially in Florida’s extreme heat, rain, and wind. It adds crucial protection beneath the panels and helps prevent moisture-related damage over time.

Synthetic underlayment is the top choice for most metal roofs, while self-adhered works best for coastal homes and high-risk areas like valleys and eaves. No matter what you choose, have it installed by a licensed roofing professional to get the protection your home needs.