Roofing Underlayment Types and Best Practices

When most people think about roofing, they think about shingles or tiles—the visible surface. But underneath that surface lies an equally important layer: the underlayment. This waterproof barrier is your roof's backup defense against water infiltration, and in Florida, it's not optional—it's required and critical.

What Is Roofing Underlayment?

Roofing underlayment is a water-resistant or waterproof barrier installed directly on your roof deck, beneath the primary roofing material. Think of it as a protective layer that:

• Provides secondary water protection if shingles fail
• Protects the deck during installation
• Adds another layer of weather resistance
• Meets building code requirements

Why Underlayment Matters in Florida

Florida's climate makes underlayment especially important:

• Heavy rain: Wind-driven rain can penetrate primary roofing
• Hurricanes: Shingles can lift or tear off; underlayment is the last defense
• UV exposure: Protects deck if shingles are damaged or blown off
• High humidity: Adds moisture barrier protection

As noted in our building codes guide, Florida has specific underlayment requirements that exceed national standards, especially in High Velocity Hurricane Zones (HVHZ).

Types of Roofing Underlayment

Asphalt-Saturated Felt (Tar Paper)

The traditional underlayment choice, felt has been used for over a century.

What It Is:

• Organic or fiberglass mat saturated with asphalt
• Available in 15-pound and 30-pound weights
• 30-pound is standard for most roofing applications

Pros:

• Lower initial cost
• Proven performance over decades
• Breathable, allowing moisture vapor escape
• Familiar to all contractors

Cons:

• Tears more easily during installation
• Can absorb water if left exposed
• Wrinkles in heat (common in Florida)
• Heavier to handle
• Shorter lifespan than synthetic

Florida Considerations:

Felt works in Florida but requires careful installation:

• Must not be left exposed for extended periods
• Can wrinkle in summer heat, causing bumps under shingles
• Not recommended for HVHZ without additional measures

Synthetic Underlayment

Modern synthetic underlayments have largely replaced felt for quality installations.

What It Is:

• Woven or spun polypropylene or polyethylene
• Typically available in various grades
• Some include slip-resistant surfaces

Pros:

• Lightweight (easier, safer installation)
• Tear-resistant (withstands installation wear)
• Lays flat in heat (no wrinkling)
• Can be left exposed longer
• Better UV resistance
• Longer lifespan (50+ years for premium products)

Cons:

• Higher material cost than felt
• Not all synthetics are equal—quality varies
• Some are vapor barriers (may trap moisture)

Florida Recommendation:

Synthetic underlayment is preferred for Florida roofs because:

• Handles heat without wrinkling
• Withstands wind during installation
• Better tear resistance during storms
• Lasts as long as or longer than the roofing above it

Self-Adhering (Peel-and-Stick) Underlayment

Premium underlayment that bonds directly to the roof deck.

What It Is:

• Rubberized asphalt with adhesive backing
• Also called ice and water shield (though Florida doesn't have ice dams)
• Creates a fully sealed barrier

Pros:

• Complete waterproof seal
• Self-seals around nail penetrations
• Required in HVHZ and vulnerable areas
• Best protection available

Cons:

• Highest cost
• More difficult to install correctly
• Cannot be easily repositioned
• Requires clean, dry deck

Florida Requirements:

Self-adhering underlayment is required by Florida Building Code in:

• High Velocity Hurricane Zones (South Florida, Keys)
• Valleys and other high-risk areas
• Around penetrations in many jurisdictions
• Edge areas in wind-prone zones

Florida Building Code Requirements

Standard Florida Requirements

At minimum, Florida requires:

• Underlayment beneath all primary roofing
• Proper overlap (typically 2-4 inches on horizontal seams)
• Fastening to resist wind
• Drip edge integration (see our flashing guide)

High Velocity Hurricane Zone (HVHZ)

In HVHZ areas (Broward, Miami-Dade counties, etc.):

• Secondary water barrier required
• Self-adhering underlayment at vulnerable points
• Enhanced attachment methods
• More stringent testing requirements

Wind-Borne Debris Region

Much of Florida is in the wind-borne debris region:

• Enhanced underlayment may be required
• Specific attachment patterns
• Compliance inspection required

Underlayment and Tile Roofs

If you have a tile roof, underlayment is especially critical:

The Tile Truth

Many homeowners don't realize:

• Tiles themselves are not waterproof on their own
• Underlayment does the real waterproofing
• Underlayment wears out before tiles (20-25 years vs 50+ years)

Underlayment Replacement

Tile roofs often need underlayment replacement:

• Tiles are removed and set aside
• Old underlayment is replaced
• Tiles are reinstalled
• Extends tile roof life another 20-25 years

This is a major project but significantly less expensive than full tile replacement.

Installation Best Practices

Deck Preparation

Before underlayment installation:

• Deck must be clean, dry, and smooth
• Replace any damaged or rotted sheathing
• Remove old roofing materials completely
• Nail heads should be flush or countersunk

Proper Overlap

Overlap requirements vary but typically:

• Horizontal seams: 2-4 inches minimum
• Vertical seams: 6 inches minimum
• Hips and ridges: 6 inches each side
• Valleys: 12 inches minimum each side

Fastening

Proper fastening prevents wind damage:

• Use cap nails or staples as specified
• Follow manufacturer spacing requirements
• Stagger fasteners to avoid weak lines
• Increase fastening at edges and high-wind areas

Weather Considerations

Installation timing matters:

• Never install on wet deck
• Self-adhering products need warmth to bond (typically 40°F+)
• Complete before rain arrives
• Protect from extended UV exposure before shingles applied

Choosing the Right Underlayment

For Budget-Conscious Projects

If cost is primary concern:

• 30-pound felt for steep slopes, dry climates
• Basic synthetic for Florida conditions
• Add self-adhering at valleys and edges
• Ensure code compliance minimum

For Optimal Protection

For best long-term performance:

• Premium synthetic underlayment overall
• Self-adhering at all penetrations, valleys, edges
• Additional self-adhering in high-risk areas
• Consider full self-adhering for maximum protection

For Specific Roof Types

Shingle Roofs:

• Synthetic preferred
• Self-adhering at valleys, penetrations, edges

Metal Roofs:

• Synthetic with high-temperature rating
• Some metal requires specific underlayment types

Tile Roofs:

• Premium synthetic designed for tile
• Self-adhering at critical areas
• Long lifespan essential (tiles outlast cheap underlayment)

Flat Roofs:

• Different system entirely (see flat roof guide)
• Membrane systems serve as primary waterproofing

Common Underlayment Problems

Premature Failure

Underlayment can fail before expected:

• Cheap materials with short lifespans
• UV degradation if exposed too long
• Improper installation
• Moisture trapped beneath

Installation Issues

Common installation problems:

• Insufficient overlap at seams
• Improper fastening (too few, wrong type)
• Wrinkles that telegraph through shingles
• Damage from foot traffic during installation

Water Vapor Problems

Some underlayments trap moisture:

• Vapor-barrier synthetics can trap attic moisture
• Causes deck rot from inside
• Especially problematic with poor attic ventilation
• Choose breathable products when possible

Cost Comparison

Typical costs for underlayment (materials only, per square):

• 15-lb felt: $10-$20 per square
• 30-lb felt: $15-$25 per square
• Basic synthetic: $20-$40 per square
• Premium synthetic: $40-$70 per square
• Self-adhering: $75-$150+ per square

Note: A 'square' is 100 square feet. Labor adds significantly to these costs.

Cost vs. Value

Consider the total picture:

• Premium underlayment costs more upfront
• Protects against water damage (thousands in repairs)
• Lasts longer (may outlast the roofing)
• Often required for best warranty coverage
• Small percentage of total roof cost

Questions to Ask Your Contractor

When getting roof quotes, ask:

• What type of underlayment is included?
• What brand and product specifically?
• Where will self-adhering be used?
• Does the underlayment meet code for my area?
• What is the underlayment warranty?

Low bids often use the cheapest underlayment. Understand what's included before comparing prices.

The Bottom Line

Underlayment is not the place to cut costs on a Florida roof. This hidden layer provides critical protection against our challenging climate. Whether you're getting a new roof or evaluating an existing one, quality underlayment installed correctly is essential for long-term performance.

At Pro Specialty Services, we use premium synthetic underlayment as standard on our roofing projects, with self-adhering products at all critical points. We believe in building roofs that last—and that starts with the layers you can't see. Contact us for a roof inspection or consultation to discuss your roofing needs.