Roof Underlayment Types & Why They Matter in Altamonte Springs, Florida

Most homeowners in Altamonte Springs spend a lot of time picking out shingles — the color, the style, the warranty. That's understandable. Shingles are what you see. But roofing contractors will tell you the layer you *can't* see is often the one that decides whether your home stays dry after a hurricane or a long Florida rainy season. That hidden layer is the underlayment, and choosing the right type matters more here than almost anywhere else in the country.

Florida's combination of intense UV exposure, high humidity, driving rain, and hurricane-force winds puts roofing systems under stresses that most northern building codes weren't designed to address. Understanding what underlayment is, how the three main types compare, and what Florida's updated building codes actually require can help you make a smarter decision the next time your roof is replaced or repaired.

What Is Roof Underlayment — and Why Is It the Real Waterproofing Layer?

Shingles are your roof's first line of defense, but they aren't truly waterproof. They're designed to shed water, not seal against it. Wind-driven rain, ice dams (rare in Florida but not impossible during unusual cold snaps), and the eventual aging of shingles all create paths for water to slip past the surface layer.

Underlayment is the water-resistant or waterproof membrane installed directly on your roof deck — between the deck and the shingles. It's the barrier that catches any water that makes it past the outer layer. In a strong storm, when shingles lift, crack, or blow off entirely, the underlayment is often the only thing standing between your attic and open sky.

That's why roofing professionals call it the secondary water barrier. It's not a backup afterthought. In Florida especially, it's arguably more important than the shingles themselves.

The Three Main Types of Roof Underlayment

Felt (Asphalt-Saturated) Underlayment

Felt underlayment — often called "tar paper" — has been used on American roofs for well over a century. It comes in two weights, commonly referred to as #15 and #30, based on the original weight per 100 square feet (though modern manufacturing has changed the actual weights somewhat).

Pros: Inexpensive, widely available, and proven over decades of use.

Cons: Felt absorbs moisture, which makes it prone to wrinkling, tearing during installation, and deterioration in humid climates. Under Florida's heat, it can dry out and become brittle quickly. It also offers very limited protection if shingles are stripped away and the roof is left exposed for any length of time before repairs can begin — which, after a major storm, could be days or weeks.

For most modern Florida re-roofing projects, felt is increasingly being replaced by better-performing alternatives.

Synthetic Underlayment

Synthetic underlayment is made from woven or spun polypropylene or polyethylene. Over the past two decades it has become the standard choice for most Florida reroofing jobs, and for good reason.

Pros: Synthetic is significantly lighter and stronger than felt. It resists tearing during installation, holds up better under UV exposure (important if the roof deck is exposed between tear-off and shingle installation), and doesn't absorb moisture. It also lays flatter, which can reduce the chance of shingle irregularities over time. Many products carry high wind and water-resistance ratings that meet or exceed Florida Building Code requirements.

Cons: Quality varies widely between manufacturers. A budget synthetic from an unknown brand may not perform as well as a name-brand felt product. Your contractor's material choices matter here.

For most sloped roofs in Altamonte Springs, a quality synthetic underlayment is the baseline expectation for any reputable reroofing job.

Peel-and-Stick (Self-Adhering) Underlayment

Peel-and-stick underlayment — also called self-adhering modified bitumen membrane — is the highest-performing option available. It bonds directly to the roof deck, creating a fully adhered, watertight seal rather than just lying on top of it.

Pros: When shingles are completely removed by wind, a peel-and-stick underlayment can keep the interior of your home dry for an extended period. It seals around nail penetrations, which is a significant vulnerability in standard underlayments. It provides excellent protection at eaves, valleys, and other high-risk areas where water tends to pool or intrude.

Cons: It costs more than felt or standard synthetic, and it requires more careful installation in high heat since it can become extremely tacky and difficult to reposition.

What Florida Building Code Requires

After the devastation of the 2004–2005 hurricane seasons, Florida significantly strengthened its roofing code. The Florida Building Code now requires a secondary water barrier on most residential reroofing projects. This typically means either a full layer of self-adhering peel-and-stick membrane, or a synthetic underlayment applied in a specific nail pattern that meets the code's requirements for wind uplift resistance.

Many insurers in Florida also want documentation that your roof meets current code standards — and some will reduce premiums or restore coverage for roofs that do. If your home has an older roof installed before these updates, it's worth having a licensed roofer evaluate whether your current underlayment would meet today's standards. A free inspection is the easiest way to find out.

Which Underlayment Is Right for Your Altamonte Springs Home?

• Re-roofing a standard sloped roof? A high-quality synthetic underlayment meeting Florida Building Code wind-uplift ratings is the minimum to consider.
• In a high-wind zone or coastal area? A full peel-and-stick system, or peel-and-stick at eaves and valleys with synthetic in the field, gives you the strongest protection.
• Filing an insurance claim after [storm damage](/services/storm-damage)? Be sure your contractor documents the underlayment type and installation method for your insurer.
• Tight budget? Even if you can't do a full peel-and-stick system, insisting on a code-compliant synthetic over felt is a meaningful upgrade at minimal added cost.

The right choice also depends on your roof's pitch, your specific location within Florida, and the requirements of your homeowner's insurance policy. A licensed local roofer can walk you through the options that make the most sense for your situation.

If you're not sure what's currently under your shingles — or you've recently had storm damage and want to know whether your roof's secondary water barrier is intact — Rune Roofing can connect you with a licensed local roofer who offers a free inspection. Don't wait until the next storm to find out. Call us today and let us match you with a trusted, vetted contractor in Altamonte Springs who can give you a straight answer about where your roof really stands.