Roof Underlayment

Roof Underlayment

Roof underlayment is the hidden protective blanket that sits between your roof deck and the visible roof covering. Think of it as the cozy sweater your house wears under its hat (the roof tiles or shingles). It keeps water, snow, and wind-driven rain from sneaking into your home if the top layer is ever damaged. Just like roof tiles, not all underlayments are alike—different materials, thicknesses, and attachment methods deliver varying levels of protection and performance. In this section, we’ll explore what underlayment is and why it matters.

Types of roof underlayment

There are several categories of roof underlayment, each designed for specific climates, budgets, and roofing systems. The three most common are synthetic underlayment, asphalt-saturated felt, and self-adhered (peel-and-stick) underlayment. Understanding these options will help you choose the right “second line of defense” for your roof.

Synthetic underlayment

Synthetic underlayments are made from durable polypropylene or polyethylene fabrics. Picture a high-tech tarp engineered to stay flexible, resist tearing, and repel water. They’re lightweight, which makes them easy for installers to handle and reduces overall roof load. Many synthetics have textured or non-slip surfaces for safer footing during installation, and they’re resistant to UV exposure, allowing them to stay uncovered for weeks without degrading—handy on large or weather-delayed projects.

Because they’re stronger and less prone to wrinkling than felt, synthetic underlayments lay flatter, helping roof coverings sit smoothly. While they can cost more per roll than felt, the added durability and lower labor time often make up the difference over the life of the roof.

Asphalt-saturated felt (traditional felt)

Asphalt-saturated felt—often called “tar paper” or just “felt”—is the classic choice that roofers have used for generations. It’s made by soaking a cellulose (paper) or fiberglass mat in asphalt, creating a water-shedding barrier. Felt is typically sold in #15 or heavier #30 weights, with the higher number indicating greater thickness and durability.

Felt underlayment is affordable and widely available, making it a budget-friendly option. However, it’s heavier than synthetic products and can wrinkle or tear if left exposed to rain or strong winds before the final roof covering is applied. In hot weather, asphalt in the felt can become sticky, which sometimes complicates installation. Still, for many straightforward roofing jobs, traditional felt remains a reliable and economical solution.

Self-adhered (peel-and-stick) underlayment

Self-adhered underlayments feature a rubberized asphalt or butyl layer with a peel-off backing. Once exposed, the underside sticks directly to the roof deck, creating a watertight seal around fasteners and along overlaps. Imagine a giant waterproof sticker that bonds so tightly it blocks ice dams and wind-driven rain from working under your shingles.

This premium underlayment is especially valuable in harsh climates—areas prone to ice, heavy snowfall, or hurricanes. It’s commonly installed along eaves, valleys, and penetrations for extra leak protection, though some high-end roofs use it over the entire deck. Peel-and-stick products cost more than felt or basic synthetics, but their superior waterproofing can save thousands in potential repairs.

Recommendations for underlayment selection

Choosing the right underlayment depends on several factors:

• Climate: In cold regions with ice dams, self-adhered underlayment along eaves is almost standard. Hot, sunny climates benefit from UV-resistant synthetics that won’t dry out quickly.
• Roof covering: Metal roofs often pair well with high-temperature synthetics or specialized slip sheets to allow for thermal movement. Asphalt shingles work with any of the three main underlayment types, though code or manufacturer guidelines may influence your choice.
• Slope: Low-slope sections (under 4:12) may require fully adhered or double-layer felt to ensure proper water shedding.
• Budget vs. longevity: Felt is typically the lowest-cost upfront, while synthetics offer a middle ground of price and enhanced performance. Self-adhered underlayments demand the highest initial investment but provide unrivaled protection.
• Installation timeline: If you expect delays between underlayment and final roof installation, opt for a synthetic rated for extended UV exposure.

What's the price range for underlayment?

Underlayment pricing varies by material, thickness, and brand. Keep in mind these figures can shift based on roof complexity, local labor rates, and regional building codes. For a precise estimate tailored to your project, request quotes from local roofing contractors — or reach out to A1 SolarStore for personalized guidance on underlayment options and costs.

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