What Is Underlayment & Why Does It Matter for Your Roof?

June 12, 2025

Summary

Underlayment is a critical layer of protection between your roof’s outer material (like shingles or metal) and the structure beneath.
It prevents water from penetrating into your home, adding an extra layer of security—especially during extreme weather.
There are different types of underlayment, including felt, synthetic, and ice-and-water shield. Each one comes with unique benefits and applications.
The right underlayment depends on your climate, budget, and roof type.
Choosing the right underlayment is just one part of protecting your roof. Rejuvenation solutions like Roof Maxx can also help your asphalt shingles last longer, while saving you up to 80% of the cost for a total roof replacement.

This interview features roofing expert Mike Feasel, who explains the importance of underlayment in a roofing system and shares insights on why underlayment can be the make-or-break element for roof durability.

Below, we explain why underlayment is so important and show you several different varieties. You’ll also learn how combining the right underlayment with roof rejuvenation and other maintenance tips can help extend the life of your asphalt shingles for years to come.

Why Roofing Underlayment Matters?

Roofing underlayment serves as a last line of defense, keeping water out if the outer roofing layer fails. This layer is essential for:

Waterproofing: Underlayment protects your home from leaks that could occur if shingles are damaged or high winds drive rain beneath them. Find more steps for preventing water damage to your home here.
Insulation: It provides an additional layer that can help improve insulation efficiency.
Durability: A high-quality underlayment can extend the life of your roof, protecting it from rot, mold, and structural damage.

Where Underlayment Fits in Your Roofing System?

Roof underlayment sits directly on top of the roof decking (usually plywood) and beneath your roof’s outer layer. Think of it as your roof’s backup raincoat—it steps in when shingles get damaged, blow off, or start to wear down.

Types of Roofing Underlayment

1. Felt Underlayment

Traditionally made from asphalt-saturated paper.
Often used under asphalt shingles.
Comes in different weights, such as 15-lb or 30-lb (these are useful indicators of durability).
Most common because it is cost-effective but with less durability than synthetic options.

2. Synthetic Underlayment

Made from polypropylene or polyethylene, making it highly tear-resistant and durable.
More resistant to high winds and extreme weather vs felt.
Won’t absorb water.
Becoming more popular, although it is also more expensive than felt.

3. Ice & Water Shield

A rubberized, self-sealing underlayment that adheres to the roof deck.
Ideal for areas prone to ice dams or heavy rain, as it provides a watertight seal.
Used along the roof’s edges, valleys, and around roof penetrations (e.g., chimneys or skylights).
Homeowners in storm-prone areas may choose to cover the entire roof with this kind of underlayment for maximum protection.

Choosing the Right Underlayment

Selecting the best underlayment depends on your budget, the roof’s intended lifespan, and your location:

Short-Term Plans: If you’re selling soon, felt underlayment might be sufficient.
Long-Term Investment: For a durable, low-maintenance roof, synthetic underlayment or ice-and-water shield is often worth the extra cost, especially in harsh climates.

What’s Best for Your Climate?

Climate	Suggested Underlayment Type	Why It Works
Cold & snowy (Midwest, Northeast)	Ice & Water Shield	Self-sealing protection against ice dams
Hot & humid (Southeast)	Synthetic	Resists mold and high heat
Mild & dry (Southwest)	Felt	Affordable and sufficient for low-rain areas
Storm-prone (coastal regions)	Full Ice & Water or Synthetic	Resists uplift and water intrusion

Extra Steps to Protect Your Roof: Roof Maxx & More

Roofing underlayment plays a valuable role in protecting your home, but you can also treat the roof shingles themselves. Roof Maxx is a plant-based penetrant that absorbs into your shingles to replace the natural oils they lose over time and help extend their lifespan by up to 15 years. Adding it can:

Make your shingles more flexible and durable
Save you money on a premature roof replacement (up to 80% more expensive)
Help improve the appearance and curb appeal of your home

In addition to solutions like Roof Maxx, consider trimming the trees around your property to minimize the chances of damage caused by falling debris—and be sure to have your gutters cleaned on a regular basis. The better you take care of your roof, the better it will take care of you.

Talk to a Trusted Roofing Contractor

For optimal performance, consult with a qualified roofing contractor who understands your local climate and building codes. An experienced contractor will:

Help you choose the best underlayment for your roof and budget.
Provide clarity on warranties and the long-term value of different underlayment types.
Ensure quality installation, which is essential to maximize your roof’s protection.

Roofing underlayment may not be the most visible part of your roof, but it is certainly one of the most important parts. Whether you’re dealing with torrential rain, hurricanes, or freezing winters, the right underlayment will keep your home safe and dry for years to come.

To find a roofing contractor in your area who can also apply solutions like Roof Maxx, use our dealer locator.