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The Role of Underlayment in a Roof System

Every roof needs moisture protection. Beneath the primary layer of roofs lies an essential barrier known as roof underlayment, which serves as the first line of defense against leaks, mold, and rot. Underlayment also supports your roof’s durability and provides extra insulation.

Whether you’re replacing your roof or installing one for your newly built property, it’s important to choose the correct type of underlayment.

In this blog post, O’Brien Construction LLC’s roofers will discuss and explore the different types of underlayment, how to choose the right kind, and how they work with other components.

What Is Roof Underlayment?

Roof underlayment is a protective layer installed between the roof deck and the roofing materials. If you’ve ever seen a roof mid-installation, it’s the black or gray material that blankets the entire deck.

Underlayment diverts any moisture that penetrates the outer layer so it doesn’t reach the roof deck. It also strengthens the roof’s durability by stabilizing the primary material and regulating temperature fluctuations, which can lead to cracking or shifting over time

Certain types of underlayment are designed specifically for the material of your roof and the pitch. For example, high-temperature underlayment is ideal for metal roofs, as these roofs absorb and radiate more heat compared to asphalt or tile and require greater heat resistance.

What Are the Different Types of Roof Underlayment?

There are a few different types of underlayment, all of which have unique properties.

The right choice depends on your roof system. For example, if you have a steep roof, you can often get away with a lighter option since water runs off quickly and doesn’t linger.

Here are the unique qualities and applications of each type of roof underlayment:

• Asphalt-saturated felt: Often called “felt paper,” this more traditional underlayment is made from organic or fiberglass material saturated with asphalt. It offers basic moisture resistance and durability, making it suitable for standard asphalt shingle roofs.
• Rubberized asphalt: This underlayment has a higher percentage of asphalt and includes rubber polymers, making it fully waterproof and self-adhering. It’s ideal for areas prone to heavy rain or ice dams, providing strong protection in leak-prone zones like valleys and eaves.
• Synthetic underlayment: Made from polypropylene or polyethylene, synthetic underlayment is lighter, more tear-resistant, and provides better UV resistance than felt. It’s known for its ease of installation and is suitable for various roof types, especially those with steep pitches.

How Does Underlayment Prevent Damage?

Roof leaks often begin with damage or gaps in the outer roofing layer from cracked shingles, displaced tiles, or worn flashing. When water penetrates, it travels downward due to gravity, seeking the path of least resistance. This is where you need the underlayment to do its job.

Without sufficient underlayment, water will reach the roof deck, soaking into the wood. This can cause rot, and in severe cases, it can lead to structural weakness. Quality underlayment allows for water resistance and keeps moisture from reaching sensitive areas, even under prolonged exposure.

How Do Roof Insulation and Flashing Work With Underlayment?

Insulation is the material installed within a roof to regulate temperature and minimize heat transfer. Placed beneath the roof deck and often in attic spaces, insulation is essential for maintaining energy efficiency and ensuring indoor comfort.

Underlayment complements your insulation by protecting it from moisture that could otherwise lead to mold or reduced effectiveness. You’ll need to install the underlayment after the insulation. This sequence allows both materials to work effectively.

Flashing protects edges and joints from leaks. You need both flashing and underlayment because together, they provide layered protection. Flashing seals the roof’s most vulnerable points, while underlayment covers the entire roof deck.

How Do You Choose the Right Underlayment Material?

Choosing the best underlayment material requires considering several key factors to ensure optimal roof performance.

Here are the main factors to consider when choosing the right underlayment material:

• Roof pitch compatibility: Make sure the underlayment you choose is suitable for your roof’s pitch, as some materials work better on steeper or flatter surfaces.
• Roofing material compatibility: Ensure the underlayment pairs well with your primary roofing material. For example, consider synthetic for metal roofs and asphalt-saturated felt for shingles.
• Moisture resistance: Consider the level of moisture protection your roof needs when choosing between water-resistant or waterproof options.
• Durability and longevity: Higher-quality underlayments may cost more upfront but offer better durability and longevity, reducing future maintenance needs.
• Ease of installation: Some underlayment types are self-adhering or easier to handle, which can be particularly beneficial for complex roof designs.

What Are Signs You Need Underlayment Repair or Replacement?

Roof underlayment can deteriorate from extended UV exposure and physical damage, while improper installation or contact with sharp objects can further compromise its integrity.

Here are several key signs that your underlayment may need repair or replacement:

• Leaks or water stains indoors: Water spots or stains on your ceilings or walls are a common indicator of damaged underlayment, as moisture seeps through the roof and reaches your interior spaces.
• Shingle damage or warping: Damaged, cracked, or curling shingles can expose the underlying layer to weather elements, causing deterioration.
• Moisture or mold in the attic: If you notice dampness, mold, or mildew in your attic, it’s a sign that water is bypassing the underlayment and infiltrating your home.
• Tears or exposed sections: Visible tears, worn-out spots, or exposed areas in the underlayment indicate significant damage, which will require immediate repair or replacement.

It’s essential to regularly inspect your roof underlayment, though a thorough evaluation often requires lifting shingles to assess its condition accurately. While underlayment can typically last for several decades, environmental factors and general wear and tear may require earlier intervention. If you notice any signs of damage, it’s best to schedule an inspection as soon as you can.

Check Your Underlayment With a Roof Inspection

If you’re starting a new roofing project or have concerns about the integrity of your underlayment, materials, or other components, a roof inspection can help ensure everything is in good condition.

O’Brien Construction LLC’s professionals can help you choose the right material and install your system to ensure long-lasting protection and performance. You can reach us at (720) 245-1100.