Overview

Your shingles provide the first layer of protection against the weather, but they aren't the only materials keeping water out of your home. Roof underlayment adds a secondary barrier that helps protect the structure beneath. In this blog, Black Anchor Roofing's roofing contractors explain how underlayment works, the different materials available, and what happens when this protective layer becomes damaged or needs replacement.

Highlights

Introduction

Your shingles are the first line of defense against rain, but what happens when water finds its way beneath them? That's where roof underlayment comes in. Installed directly over the wooden roof decking, this material forms an important part of the roofing system, even though it remains hidden once the shingles are in place.

Because underlayment is concealed beneath your shingles, damage can go unnoticed until moisture reaches the roof decking or interior of your home. Understanding how this layer works and what can compromise it can help you recognize potential roofing problems before they lead to more extensive damage.

What Does a Roof Underlayment Do?

The roof underlayment serves as a secondary barrier to manage water beneath the finished roofing materials. Its job is to direct any moisture that reaches this layer down toward the eaves, where it can drain away rather than soak into the roof's structure.

This added protection is particularly useful during storms, when strong winds can push rain through gaps around shingles and other roofing components. It helps limit the damage caused by unexpected water intrusion.

During roof installation, it also provides temporary coverage for the exposed decking until the shingles are installed, provided weather conditions remain within the material's exposure limits.

What Are the Different Types of Roof Underlayment?

No two roofs are exactly alike, and the materials beneath them aren't necessarily the same either. Roofing contractors typically choose from several types of roofing underlayment based on the roof's design, the surrounding climate, and the requirements of the roofing system.

The three main types include:

  • Felt underlayment: Traditionally used in residential roofing
  • Synthetic roof underlayment: Commonly used as an alternative to roofing felt
  • Ice and water shield: Typically used in areas requiring additional protection

Each serves a particular purpose, and some roofs require a combination of materials to provide appropriate coverage.

Felt Underlayment

Felt underlayment has been a staple in residential roofing for decades. Made from a paper-like material treated with asphalt, it creates a water-resistant layer beneath shingles.

Its biggest advantage is affordability. Felt generally costs less than newer alternatives, making it a practical choice if you want reliable protection without stretching your roofing budget.

There are some trade-offs, though. Felt can tear during installation and wrinkle if exposed to moisture for too long. It also tends to be less durable than synthetic materials. Still, when installed correctly and covered promptly, it remains a suitable choice for many asphalt shingle roofs.

Synthetic Roof Underlayment

Synthetic roof underlayment has become a popular alternative to traditional felt. Made from durable plastic-based materials, it's designed to withstand the demands of roof installation while providing a water-resistant barrier beneath shingles.

One of its biggest advantages is its strength. It's lightweight, resists tearing, and generally handles exposure to rain better than felt. This can be especially useful when unpredictable weather interrupts a roofing project.

The main drawback is cost. Synthetic products typically cost more than felt, although their durability can make the added expense worthwhile. If you’re replacing your roof, it's an option worth considering for dependable protection.

Ice and Water Shield

Some parts of a roof are more likely to develop leaks than others. Ice and water shields help protect these trouble spots by sticking directly to the wooden roof decking and forming a waterproof barrier.

You'll typically find them along roof edges, in valleys where two slopes meet, and around chimneys. These are places where rainwater can collect or where melting snow can work its way beneath the shingles.

They’re usually installed alongside felt or synthetic underlayment, rather than on their own. This way, the most leak-prone areas get extra protection while the rest of the roof is covered by standard underlayment.

How Is Roofing Paper Installed?

Roofing paper is laid across the roof decking before the shingles go on. Installation starts at the bottom of the roof and moves upward, with each row overlapping the one below to help rainwater run over the seams.

The process generally involves four steps:

  • Roof preparation: Removing debris and checking the wooden decking for damage before installation
  • Initial placement: Laying the first sheet horizontally along the lower edge of the roof
  • Sheet alignment: Overlapping each new row with the one below to prevent water from slipping between the seams
  • Fastening: Securing the paper with approved fasteners according to the manufacturer's instructions

Once the paper is in place, the shingles and remaining roofing components can be installed.

Can You Shingle a Roof Without Underlayment?

Shingles shouldn’t be installed without an underlayment. Even properly installed shingles can allow wind-driven rain to reach the roof decking, leaving the wood vulnerable to moisture damage without that extra layer of protection.

Roofing paper is also required by many building codes, which establish minimum standards for safe and reliable roof construction. Shingle manufacturers also have installation requirements that must be followed to maintain warranty coverage. Skipping a required layer could leave you financially responsible for repairs that might otherwise be covered.

What Damages Roofing Paper?

Roofing paper is designed to sit beneath shingles, where it's protected from direct exposure to the elements. However, several conditions can weaken or damage it over time.

Common causes include:

  • Storm damage: High winds can lift or tear away shingles, exposing the underlayment to rain and flying debris.
  • Falling debris: Branches and other objects can puncture roofing materials, potentially damaging the underlayment beneath.
  • Prolonged sun exposure: Underlayment left exposed beyond its rated exposure period can weaken or deteriorate.
  • Trapped moisture: Water trapped beneath roofing materials can cause deterioration, particularly in moisture-sensitive underlayment.
  • Installation damage: Foot traffic, improper fastening, or careless handling during roofing work can cause tears, punctures, or shifting.

Some damage occurs during installation, while other problems develop after storms or prolonged exposure to unfavorable conditions.

Can a Roof Underlay Be Repaired?

Damaged roof underlayment can sometimes be repaired, depending on the extent of the damage and the condition of the surrounding material. Small tears or punctures may be addressed by removing the shingles above the affected area and installing a compatible patch or replacement section.

However, repairs may not be practical if the material has deteriorated across a large area or can no longer provide reliable protection. In these cases, replacement is generally the better approach. Any repair should also address the source of the damage to prevent the problem from returning.

When Does Underlayment Need To Be Replaced?

Roof underlayment doesn't have a universal replacement schedule. Its service life depends on the material, installation quality, and conditions it has experienced.

Replacement may be necessary when the underlayment is extensively torn, brittle, deteriorated, or no longer able to provide an effective water-resistant barrier. Widespread moisture damage or prolonged exposure following the loss of shingles can also make replacement necessary.

Underlayment is also commonly replaced during a complete roof replacement, when the existing material is exposed and its condition can be evaluated. If the roof is otherwise performing well and there's no evidence of damage, however, removing intact shingles solely to replace the underlayment is generally unnecessary.

Can Underlayment Be Replaced Without Replacing the Shingles?

You can sometimes replace damaged underlayment without replacing your entire shingle roof. However, the shingles covering the affected area must first be removed to access the material underneath.

Whether those shingles can be reused depends on their condition and how easily they can be removed. Newer, flexible shingles may be suitable for reinstallation, while older or brittle shingles are more likely to crack, tear, or lose their ability to seal properly during removal.

The extent of the underlayment damage determines how much of the roof must be opened up. A localized problem may only require removing shingles from a small area, while widespread deterioration can involve stripping much larger sections of the roof. In those cases, replacing the shingles along with the underlayment may be more practical than attempting to reuse them.

When Should You Call a Roofing Contractor About Your Roof Underlayment?

Since underlayment is hidden beneath your shingles, it's difficult to tell when something is wrong. However, certain warning signs may indicate that moisture is getting past your roof's protective layers.

Consider calling a roofing contractor if you're:

  • Noticing water stains spreading across your ceilings or attic surfaces
  • Finding damp or discolored wood in your attic
  • Discovering missing, cracked, or lifted shingles after a storm
  • Experiencing recurring leaks despite previous roof repairs
  • Uncovering signs of water damage during a roof replacement

These issues don't always mean the underlayment is damaged. A professional inspection can identify the source of the problem and determine whether repairs or replacement are necessary.

Hire a Trusted Roofing Company Today

Roof underlayment may be hidden beneath your shingles, but its condition can make a real difference when bad weather hits. Whether you're replacing an aging roof or dealing with a stubborn leak, keeping this protective layer in good shape helps prevent moisture damage down the road.

Black Anchor Roofing handles roof installation, repairs, and replacement, including work involving damaged or deteriorating underlayment. Our team makes sure the materials beneath your shingles receive the same attention as the rest of your roof.

Ready to get your roof and underlayment back in shape? Call (410) 205-9562 to schedule our roofing services.