Key Takeaways:
- Avoid Felt: Asphalt saturated felt is outdated for the Florida climate.
- Go Synthetic or Rubber: Use synthetic underlayments for standard protection and rubberized asphalt (peel and stick) for premium storm protection.
- Check the Deck: Always tear off old layers to inspect the roof deck before installing new roofing underlayment.
- Insurance: Ask if your choice of underlayment qualifies for an SWR (Secondary Water Resistance) discount.
Most homeowners focus on shingles, tiles, or metal panels, but the unsung hero of Florida roofing systems is the roof underlayment beneath the primary materials. Our state’s climate is designed to test the limits of building materials, and when a Category 3 hurricane churns off the coast, or when a typical Florida afternoon thunderstorm dumps three inches of rain in an hour, your dimensional shingles are only the first line of defense. The real hero, or the point of failure, is the roof underlayment.
What Is Roof Underlayment?
Roof underlayment is a protective, water-resistant, or waterproof barrier, typically made from materials such as rubberized asphalt or synthetic materials. It is installed directly on your roof deck (the plywood or OSB sheathing) beneath the outer roofing layers such as asphalt shingles, tile, or metal.
The Role of Underlayment in the Roof System
Underlayment acts as the final line of moisture protection, shielding your roofing system from wind-driven rain and helping to prevent leaks, damage, and mold. It protects the roof sheathing and the interior of your home from moisture intrusion. In Florida, where wind-driven rain can defy gravity and move horizontally, a high-quality underlayment ensures that water slipping past the roof shingles drains off the roof rather than soaking into the wood.
Think of your roof covering (the shingles or tile) as a windbreaker. It sheds most of the water and takes the brunt of the wind. The roofing underlayment is the raincoat worn underneath. If the windbreaker rips or water gets driven up the sleeves (or under the shingles), the raincoat keeps you dry.
What does roofing underlayment do?
- Moisture Barrier: It prevents rain from reaching the roof deck if shingles blow off.
- Temporary Protection: During a roofing project, it keeps the house dry after the old roof is torn off but before the new roof covering material is installed.
- Chemical Barrier: It separates the roofing material from the roof decking, preventing chemical reactions (common with asphalt shingles on resinous wood) or heat transfer issues.
Florida Underlayment Requirements
- Code-compliant: Must meet the Florida Building Code (FBC), which is essential for insurance and inspections.
- Wind resistance: Needs high uplift resistance to withstand hurricanes and strong winds.
- Waterproof: Must act as a strong barrier against intense, wind-driven rain.
- UV resistance: Should be able to withstand prolonged sun exposure during installation delays. Proper installation: Overlaps must be at least 2 inches horizontally and 6 inches vertically.
Statewide Underlayment is mandatory. The type, weight, and installation method (e.g., lap sealant) are dictated by the roof’s slope, the FBC section for the specific roof covering (shingle, tile, etc.), and the building’s wind speed designation.
Wind-Borne Debris Regions (Key Term): For roofs located in these regions (which include HVHZ), the FBC requires a much more robust system: a sealed deck using self-adhering membrane or tape applied to the deck sheathing before underlayment, followed by an approved underlayment, and then the roof covering. This is a critical hurricane mitigation detail.
Local Amendments: Always check with the local building department. Some counties (like those in HVHZ) have their own product approval lists and additional rules.
Types of Compliant Roofing Underlayment for Florida
When you receive a quote from a roofing contractor, you’ll typically see one of three options listed. Understanding the difference between these roofing underlayment types is critical for ensuring structural integrity.
Asphalt-Saturated Felt (The Traditional Choice)
For decades, this was the only game in town. Often called tar paper or felt paper, this is made from a natural base (like wood pulp or polyester) saturated with asphalt to make it water-resistant.
- Composition: A flexible base layer saturated in asphalt.
- Pros: It is inexpensive and breathable.
- Cons: It tears easily during installation, wrinkles when wet, and dries out rapidly in Florida heat, becoming brittle.
Is roof underlayment the same as tar paper?
Technically, yes, tar paper is the colloquial term for asphalt saturated felt. However, modern felt underlayment has evolved slightly from the true “tar” papers of the early 20th century, though the limitations remain.
Synthetic Underlayment (The Modern Standard)
Over the last 20 years, synthetic underlayments have largely replaced felt. These are typically made from woven polypropylene or polyethylene.
- Composition: A coarse woven material often with a polymer film bonded to the surface for slip resistance.
- Pros: Synthetic roof underlayment is incredibly tear-resistant, lighter than felt, and UV resistant (it can be left exposed for weeks). It is a non bitumen synthetic product that doesn’t dry out.
- Cons: Slightly more expensive than felt. If it’s not installed correctly so it’s breathable, it can trap moisture in the attic if ventilation is poor.
Rubberized Asphalt Underlayment (The Florida Gold Standard)
This is the premium option, often referred to as “peel-and-stick.” Rubberized asphalt underlayment contains higher percentages of asphalt and rubber polymers, creating a material that is flexible and sticky.
- Composition: Polymer modified bitumen with an adhesive back.
- Pros: It is self sealing. If a nail is driven through it, the asphalt seals around the shank of the nail, maintaining a waterproof seal. It adheres tightly to the roof deck, creating a protective membrane.
- Cons: It is the most expensive option and can be difficult to remove once installed.
Why Underlayment Matters More in Florida
In calmer climates, roof underlayment is a backup plan. In Florida, it is a structural necessity. The unique combination of high winds, intense UV radiation, and salt air requires a roofing system that is robust from the bottom up.
The Threat of Wind-Driven Rain
Florida hurricanes and tropical storms create pressure differentials. Wind can lift asphalt shingles or tile shingles just enough to force water underneath. If you are using a basic felt underlayment held down by staples, that water will find the holes and rot your roof decking.
Rubberized asphalt underlayments are critical here. Because they adhere directly to the entire roof deck, water cannot migrate laterally beneath the membrane.
Secondary Water Resistance (SWR)
This is a crucial term for Florida homeowners. Insurance companies often offer discounts for Secondary Water Resistance. This generally refers to a self sealing underlayment (peel-and-stick) applied directly to the sheathing, or a high-end synthetic roofing underlayment that is taped at all seams to create a sealed barrier.
UV Degradation and Heat
Florida roofs get hot—upwards of 160°F in the summer. Asphalt saturated felt contains volatile compounds that evaporate in this heat, causing the material to crumble over time. Synthetic underlayments and rubberized asphalt are engineered to resist heat and maintain their flexibility for the life of the roof.
Comparative Analysis: Choosing the Right Material
To help you decide which underlayment materials are right for your roofing project, I’ve broken down the key factors below.
| Feature | Asphalt-Saturated Felt | Synthetic Underlayment | Rubberized Asphalt (Peel & Stick) |
| Cost | Low ($) | Moderate ($$) | High ($$$) |
| Durability | Low (tears easily) | High (woven/tough) | Very High (flexible/elastic) |
| Water Resistance | Water-shedding (absorbs some) | Water resistant | Waterproof |
| Florida Suitability | Poor | Good | Excellent |
| Lifespan | 10-15 years | 25-50 years | 50+ years |
| Self-Sealing? | No | Generally No | Yes (around nails) |
Cost Implications
While rubberized asphalt costs more upfront (often double the price of felt underlayment), the cost of moisture damage repair is significantly higher. For a standard 2,000 sq. ft. roof, upgrading to a full peel off membrane system might add $1,500 to $3,000 to the total project, but it effectively waterproofs the entire roof regardless of what happens to the shingles.
Critical Installation Zones: Where the Leaks Happen
Even if you don’t use peel-and-stick on the entire roof, you must use it in vulnerable areas. A competent roofing contractor will insist on extra protection where roof planes meet (valleys) and around roof penetrations.
Valleys and Eaves
Valleys funnel massive amounts of water. In colder climates, ice dams are a concern at the roof edge, requiring rubberized asphalt. In Florida, while we don’t get ice dams, we get “water dams” from backed-up gutters during torrential downpours. Using rubberized asphalt underlayments at the eaves and valleys is non-negotiable.
Penetrations
Anywhere a pipe, vent, or chimney cuts through the roof deck, there is a risk. Plumbing vents, cooling systems, and other roof penetrations rely on flashings, but the underlayment acts as the gasket. Rubber like materials found in modified bitumen gaskets around these penetrations are better than rigid synthetic or felt.
Frequently Asked Questions
As Central Florida roofers working with homeowners from coast to coast, we get these underlayment questions most often.
Is underlayment necessary for a roof?
Yes. Is roofing underlayment necessary? Absolutely. Building codes, including the Florida Building Code, mandate it. Without it, your roof decking would rot within months, and your roof shingles would deteriorate prematurely due to resin pockets in the wood sheathing. It provides a layer of protection that is vital for roof durability.
What is the most common underlayment for roofing?
Currently, synthetic roofing underlayment is the most common. It offers the best balance of cost and performance for the average roof. However, in coastal Florida markets, full rubberized asphalt is becoming the standard due to insurance incentives.
How often should roof underlayment be replaced?
How often should roof underlayment be replaced? Every time the roof covering is replaced. Never install a new roof over old underlayment. The underlayment materials age just like the shingles. To ensure a water resistant roof, you must strip the entire roof down to the deck and inspect the wood before laying new roof underlayments.
What is the best underlayment to use on a roof?
For Florida, the best underlayment to use on a roof is a fully adhered rubberized asphalt underlayment. It provides the highest level of wind uplift resistance and waterproofing. If budget is a constraint, a high-grade synthetic underlayment with taped seams is a strong runner-up.
Is roof underlayment the same as tar paper?
No. While some people still use the terms interchangeably, tar paper refers specifically to organic felt paper saturated in asphalt. Modern synthetic underlayments and rubberized asphalt are chemically different, utilizing synthetic polymers and rubber polymers for superior performance.
Drawbacks and Considerations
I want to be transparent: there are exceptions.
Ventilation Issues
If you use a completely impermeable rubberized asphalt over the entire roof deck, you are essentially wrapping your attic in plastic. If your home does not have adequate soffit and ridge ventilation, this can trap humidity inside the attic, leading to mold. Consult your roofing contractor to ensure your intake and exhaust ventilation is balanced before choosing a fully impermeable roof system.
Cost Overkill?
On extremely steep roof planes (like A-frames) where water runs off instantly, or on simple gable roofs in inland areas with heavy tree cover (blocking wind), a high-end synthetic roof underlayment may be perfectly sufficient. You may not need to pay the premium for rubberized asphalt on the entire roof system, only at the eaves and valleys.
Maintenance and Lifespan
Roof underlayment generally requires zero maintenance because it is buried beneath roofing materials. However, its lifespan is tied to exposure.
If a storm blows off your shingles, synthetic underlayments can withstand UV exposure for 3 to 6 months (depending on the brand) without failing. Asphalt saturated felt will wrinkle and degrade within days of exposure. Rubberized asphalt is incredibly durable but can be unsightly if exposed for long periods.
To avoid costly repairs, have your roof inspected after any major storm. If shingles are missing, your underlayment is your only shield.
The Verdict: Don’t Skimp on the Layer You Can’t See
In the roofing industry, we often say the roof covering material is for looks, but the underlayment is for life.
Florida’s climate and weather put roofs under stress that shingles alone can’t handle. The roofing underlayment is the primary moisture shield that protects the home when wind-driven rain gets under shingles or when shingles blow off in high winds.
In Florida, underlayment is not just a secondary layer, it’s an invisible hero protecting your home and your pocket.
When planning your next roofing project, ask your roofer about the brand and type of underlayment they intend to use. Investing in a high-quality underlayment, specifically a synthetic underlayment or rubberized asphalt, is the smartest insurance policy you can buy for your home.
Your roof is a system. Ensure every layer of protection, from the roof decking up to the weather surface, is built to weather the storm.
