Franciscus Roofing

A roof replacement includes more than just new shingles. One of the most important components is the underlayment, a hidden layer that plays a key role in protecting the structure beneath the surface.

Many homeowners are unfamiliar with roof underlayment until they begin planning a roof replacement. It’s not visible once the roof is complete, but it supports the entire system and can affect how long the roof lasts.

Different types of underlayment exist, and not all are the same. Selecting the right one depends on your roofing material, the climate, and the condition of your roof deck.

This article explains the basics of roof underlayment, how it works, and how to compare your options when replacing a roof.

What Is Underlayment For Roofing

Roof underlayment is a water-resistant or waterproof barrier that installs directly onto the roof deck, underneath the shingles or other outer roofing materials.

Its main purpose is to provide a secondary layer of protection if water gets past the shingles. This helps prevent leaks that could damage the structure or interior of the home.

Underlayment also shields the roof deck during the installation process. It covers and protects the wood surface before the final roofing layer is applied.

Additionally, roof underlayment supports the performance of the top roofing material. It can improve wind resistance and help the shingles lie flat and stay in place.

Historically, builders used asphalt-saturated felt paper as the standard underlayment. Over time, synthetic underlayments and self-adhering membranes have become more common due to their durability and resistance to tearing.

Shingle Underlayment Types Compared

There are three common types of underlayment used for shingle roofing: asphalt-saturated felt, synthetic underlayment, and rubberized asphalt underlayment. Each type has different material properties, costs, and performance characteristics.

1. Asphalt-Saturated Felt

Asphalt-saturated felt is made from either an organic or fiberglass base that is saturated with asphalt. It is one of the oldest roofing paper types still in use today.

Felt underlayment comes in two common weights: 15-pound and 30-pound. The 30-pound version is thicker and more durable than the 15-pound version.

This felt paper for roof applications was the industry standard before synthetic alternatives became popular. It remains the most economical option for basic roofing needs.

However, it has limitations:

• Tears easily: Especially when wet or during windy installations
• Absorbs moisture: Can wrinkle and lose effectiveness when exposed to rain
• UV sensitivity: Breaks down quickly when exposed to sunlight
• Limited lifespan: Typically lasts 5-15 years for 15-pound felt and 15-20 years for 30-pound felt

Felt underlayment works best on budget-conscious projects or in areas with mild weather conditions where extreme protection isn’t necessary.

2. Synthetic Underlayment

Synthetic roof underlayment is made from engineered polymers such as polypropylene or polyethylene. These materials create a lightweight, water-resistant barrier that resists tearing.

Synthetic underlayment offers several advantages during installation:

• Stronger construction: Less likely to tear during installation
• Weather resistant: Can remain uncovered for 3 to 6 months
• Lightweight: 5 to 10 times lighter than felt underlayment
• Greater coverage: Covers more area per roll, reducing seams

Though its initial cost is higher, synthetic underlayment may reduce labor time due to its larger coverage area and easier handling. It typically lasts two to three times longer than traditional felt.

This type of underlayment has become the standard for quality roofing projects. It works well in areas with variable weather conditions and on complex roof designs where installation might take longer.

3. Rubberized Asphalt Underlayment

Rubberized asphalt underlayment is a self-adhering membrane made from rubber-modified asphalt. It has an adhesive backing that sticks directly to the roof deck.

This type of underlayment is fully waterproof rather than just water-resistant. It also self-seals around nails and fasteners, helping to prevent leaks.

While rubberized asphalt underlayment costs more than other types, it offers superior protection in critical areas:

• Along eaves where ice dams form
• In valleys where water collects
• Around roof penetrations like chimneys and vents
• On low-slope sections where water drains slowly

This material is temperature-sensitive during installation, requiring warmer conditions for proper adhesion. It’s commonly referred to as “peel and stick roof underlayment” because of its installation method.

Key Factors In Choosing The Best Roofing Underlay

The best roofing underlayment depends on multiple factors. There is no single product that fits every home or situation.

Climate And Regional Considerations

Underlayment selection is directly influenced by local weather patterns. In colder climates like Northeast Ohio, ice and snow accumulation can lead to ice dams, requiring waterproof underlayment along the eaves.

High winds and wind-driven rain can compromise less durable underlayments. Areas with frequent storms benefit from synthetic or rubberized asphalt options that resist tearing.

Temperature fluctuations cause roof materials to expand and contract. Underlayment that maintains flexibility in both hot and cold conditions helps reduce stress on the overall roofing system.

In humid environments, moisture buildup under the roof can lead to mold or wood rot. Some synthetic underlayments allow limited breathability, which helps manage moisture levels.

Cost And Life Expectancy

Different underlayment types have different costs and lifespans:

Underlayment Type	Initial Cost	Typical Lifespan	Best For
Asphalt Felt (15lb)	$	5–15 years	Budget projects, temporary roofs
Asphalt Felt (30lb)	$$	15–20 years	Traditional builds in mild climates
Synthetic	$$$	25–50 years	Premium roofs, harsh weather exposure
Rubberized Asphalt	$$$$	30–50 years	Areas prone to ice dams, critical waterproofing

Higher-cost underlayments generally last longer and offer increased protection. In some situations, the higher upfront cost may result in fewer repairs and longer roof life.

Manufacturer Warranty Requirements

Most roofing shingles come with a manufacturer warranty. These warranties often include specific requirements about the type of underlayment that must be used.

Using an underlayment not approved by the manufacturer may void the warranty. Each manufacturer has its own guidelines, which are based on how their products interact with the underlayment.

Professional installation also affects the warranty. If the underlayment is installed incorrectly, it could result in reduced coverage or denial of future claims.

Which Underlayment Is Best For Asphalt Shingles

Synthetic underlayment is generally the best choice for asphalt shingle roofs. It provides excellent water resistance, durability, and longevity that complements modern shingle systems.

Synthetic roof underlayment has largely replaced traditional felt in professional installations. It provides consistent performance and holds up well under varying weather conditions.

Different roof sections may benefit from specific underlayment types:

• Standard roof areas: Synthetic underlayment works well across most of the roof surface due to its tear resistance and durability
• Budget projects: 30-pound felt offers basic protection at a lower cost, though with a shorter lifespan
• Vulnerable areas: Rubberized asphalt (peel and stick) underlayment provides extra protection in valleys, around penetrations, and along eaves
• Complete protection: Many roofers use synthetic underlayment across the entire roof with rubberized asphalt in high-risk areas

The choice of roof underlayment for asphalt shingles ultimately depends on the specific roof design, local weather patterns, and budget considerations.

Should You Use Peel And Stick Or Felt Paper For Roof

Peel-and-stick membranes and felt paper serve different purposes on a roof. They’re often used together, with each material placed where its properties provide the most benefit.

1. Peel And Stick Characteristics

Peel-and-stick underlayment creates a waterproof seal wherever it’s applied. This self-adhering membrane excels in specific roof locations:

• Eave protection: Prevents water infiltration from ice dams in cold climates
• Valley reinforcement: Adds waterproofing where two roof planes meet and direct water
• Low-slope areas: Provides extra protection where water drains more slowly (less than 4:12 pitch)
• Hurricane regions: Sometimes used across the entire roof in storm-prone areas
• Penetration protection: Creates watertight seals around chimneys, vents, and skylights

The best peel and stick roof underlayment products feature high adhesion strength, flexibility in temperature changes, and long-term waterproofing capabilities.

2. Felt Paper Characteristics

Felt paper underlayment has been used in roofing for decades. This traditional material still has specific applications:

• Budget-friendly option: Costs less than synthetic or rubberized asphalt options
• Compatibility: Works well with older roofing systems and traditional building methods
• Breathability: Allows some moisture vapor to pass through, which can benefit certain roof designs
• Code compliance: May be required by local building regulations in some areas

This underlay for roofing felt provides basic water resistance. While not as durable as newer materials, it remains useful for specific applications where its characteristics align with project requirements.

How Long Does Roofing Underlayment Last

Roofing underlayment should last as long as the roofing material installed above it. For most asphalt shingle roofs, this means 20-30 years, though premium materials can last longer.

Several factors affect underlayment lifespan:

• Material quality: Synthetic and rubberized asphalt underlayments typically outlast traditional felt by 10-30 years
• Installation technique: Proper fastening, overlapping, and surface preparation significantly impact longevity
• Weather exposure: Extreme temperatures, UV radiation, and moisture all accelerate degradation
• Attic ventilation: Proper airflow reduces heat and moisture buildup that can damage underlayment from below

When installed correctly and paired with appropriate roofing materials, modern underlayments provide decades of protection. This makes them a worthwhile investment in the overall roofing system.

Ready To Protect Your Home With A Trusted Roofing Expert

Selecting the correct roof underlayment depends on material type, climate, and expected lifespan. Regional weather patterns in Northeast Ohio—such as snow, ice, and rain—make it necessary to evaluate each roof individually.

Underlayment performance also depends on proper installation. Factors such as fastening, overlap, and temperature at installation time affect long-term durability. Even high-quality materials can fail if not installed according to manufacturer guidelines.

Franciscus Roofing has installed roofing systems across Northeast Ohio for more than 25 years. Our team selects materials designed for the local climate and installs them to meet all manufacturer specifications.

Homeowners interested in scheduling a roof inspection or requesting an estimate can do so by visiting: https://1866staydry.com/ez-quick-quote/.

FAQs About Roof Underlayment

Can I install a new roof over existing underlayment?

While it’s technically possible in some cases, installing new roofing over old underlayment isn’t recommended because existing underlayment may hide deck damage and can reduce the new roof’s effectiveness and lifespan.

How does underlayment affect roof ventilation?

Properly installed underlayment works with roof ventilation systems by creating a barrier that still allows moisture to escape from the attic, preventing condensation while maintaining the roof’s water resistance.

What underlayment is best for metal roofs?

Synthetic underlayments are typically preferred for metal roofs because they can withstand the high temperatures that develop under metal roofing and provide a smooth, stable base that reduces noise and prevents damage to the metal panels.