Best Roof Underlayment in 2026: How to Choose the Right Type for Your Roof

Your shingles get all the attention, but the layer underneath them is what actually keeps your home dry. Roof underlayment sits between your roof deck and your roofing material, and it is the last line of defense when rain, wind, or ice gets past the surface. Pick the wrong one and you are looking at leaks, rot, and expensive repairs years before your roof should need work.

The problem is that most homeowners and even some contractors do not spend enough time on this decision. There are three main types of roof underlayment on the market, and each one performs differently depending on your climate, your roofing material, and how long you need it to last.

This guide breaks down all three types, compares them where it matters, and helps you pick the right roof underlayment for your project without overpaying or underprotecting.

What Is Roof Underlayment and What Does It Do?

Roof underlayment is a sheet material installed directly on top of the plywood or OSB roof deck before the shingles, metal panels, or tiles go on. It covers the entire deck surface and creates a continuous moisture barrier that protects the wood structure underneath.

It does three things that your roofing material alone cannot do.

First, it catches water that gets past the shingles. Wind driven rain, cracked shingles, lifted tabs, and nail holes all allow small amounts of water through. The underlayment stops that water from reaching the wood deck where it causes rot and mold.

Second, it protects the deck during construction. There is always a gap between when the deck is built and when the final roofing material is installed. Rain during that window soaks into bare wood and causes swelling, warping, and mold. Underlayment keeps the deck dry until the roof is finished.

Third, it provides emergency backup. If a storm tears off shingles, the underlayment gives your home temporary protection until repairs happen. This single benefit has prevented thousands of dollars in interior water damage during hurricanes and severe weather events.

Building codes require roof underlayment on virtually all residential roofing projects. And nearly every shingle manufacturer requires it for their warranty to remain valid. If you skip it or use the wrong type, you could void the warranty on a roof that cost $15,000 to $25,000.

The Three Types of Roof Underlayment

Every roof underlayment product on the market falls into one of three categories. Here is how each one works and where it fits.

Asphalt Saturated Felt

Felt paper, sometimes called tar paper, is the traditional option that roofers have used for decades. It is made from paper or fiberglass fibers soaked in asphalt to create a water resistant sheet. It comes in two weights: 15 pound and 30 pound. The 30 pound version is thicker, stronger, and provides better moisture protection.

Felt is the cheapest option per roll. It works on basic residential projects in mild climates where the shingles will be installed within a day or two of laying the underlayment.

The downsides are significant. Felt absorbs water and wrinkles when it gets wet. It tears easily under foot traffic and tool drops. It degrades quickly in direct sunlight, so if your project gets delayed even a few days, the exposed felt is already losing its protective ability. And it lasts only 10 to 20 years under the roofing material, which means it can fail while your shingles still have a decade of life left.

For a deeper look at how felt stacks up against modern alternatives, our synthetic vs felt comparison covers every detail.

Synthetic Underlayment

Synthetic roofing underlayment is made from engineered polypropylene or polyethylene polymers. It is the most popular choice among modern roofers and is quickly replacing felt as the standard for shingle roofs.

Synthetic does not absorb water. It stays flat and functional even if it gets rained on during installation. It is much stronger than felt, resisting tears from boots, tools, and rough handling on the job site. Most synthetic products can handle 60 to 180 days of direct UV exposure without degrading, giving your crew flexibility if there are weather delays.

Each roll of synthetic covers 400 to 1,000 square feet compared to 200 for felt, which means faster installation, fewer seams, and fewer trips up the ladder. And synthetic lasts 25 to 40 years, matching or outlasting the roofing material above it.

The cost per roll is higher than felt ($50 to $130 vs $20 to $30), but per square foot of actual coverage, synthetic is often comparable. When you factor in faster installation time and fewer callbacks, it typically costs less on the total project.

Rubberized Asphalt (Ice and Water Shield)

Rubberized asphalt is a self adhesive membrane that bonds directly to the roof deck and creates a fully waterproof seal. It seals around nail penetrations, which is something neither felt nor synthetic can do. This makes it the strongest moisture barrier available.

This type of underlayment is not used across the entire roof on most projects. Instead, it is installed in the areas most vulnerable to water problems: along the eaves where ice dams form, in roof valleys where water concentrates, and around penetrations like chimneys, skylights, and vent pipes.

Building codes require ice and water shield at the eaves in cold climates. Many codes also require it in valleys regardless of climate. The most effective roofing systems use rubberized asphalt in the high risk areas and synthetic underlayment across the rest of the deck.

Rubberized asphalt costs more than synthetic, but for the targeted areas where it is used, the extra cost is worth it.

How to Choose the Right Type for Your Roof

The best roof underlayment for your project depends on four things: your climate, your roofing material, your project timeline, and your budget.

Climate. Hot, sunny climates need underlayment with strong UV resistance. Synthetic performs well here. Cold climates with freezing temperatures need ice and water shield at the eaves and valleys, paired with synthetic across the rest of the deck. Wet climates need maximum water resistance, which rules out felt in most cases. If you are in a hot and humid region, our attic insulation guide for hot climates explains how the right underlayment and insulation work together.

Roofing material. Standard synthetic works well under asphalt shingles. Metal roofs need products rated for higher temperatures (220 degrees Fahrenheit minimum). Tile and slate require premium grade synthetic with extra tear strength to handle the weight during installation. Our underlayment for shingles guide covers shingle specific requirements in detail.

Project timeline. If shingles go on within days, economy grade synthetic works fine. If there could be weeks of exposure between underlayment and final roofing, choose a product with a longer UV rating (90 to 180 days).

Budget. Felt saves money upfront but costs more over the life of the roof. Synthetic costs a bit more per roll but covers more area, installs faster, and lasts longer. For most projects, synthetic delivers the best value overall.

Which Type Should You Use? Quick Decision Guide

Use synthetic underlayment across the full deck if: You want the best balance of performance, durability, and value. You are installing asphalt shingles, metal, tile, or slate. Your deck might be exposed to weather for more than a day or two before the final roofing goes on.

Add ice and water shield at eaves, valleys, and penetrations if: You live in a cold climate with freezing temperatures. Your roof has valleys, dormers, or complex angles. You have skylights, chimneys, or other roof penetrations.

Use felt only if: You are on an extremely tight budget, the roof is simple and small, the climate is mild, and the shingles will be installed the same day the underlayment goes down.

What About Waterproof Roof Underlayment?

Many homeowners search for waterproof roof underlayment expecting a single product that handles everything. Here is the reality.

Synthetic underlayment is highly water resistant. Rain hits the surface and runs right off. But it is not a fully sealed membrane. Water can still get through at nail penetrations and seam overlaps under extreme conditions.

Rubberized asphalt (ice and water shield) is truly waterproof. It self seals around nails and bonds directly to the deck. But it costs significantly more and is not practical for the entire roof on most budgets.

The best approach is using both together: ice and water shield in the vulnerable areas and synthetic across the rest. This gives you full waterproof protection where you need it most without blowing your budget on areas where water resistant is more than enough.

BCP RoofLayer: Built for the Way Roofing Actually Works

At BCP Inc., we make roof underlayment for contractors and homeowners who want the job done right. Our RoofLayer product line includes three grades designed for different projects:

RoofLayer Eco is our economy grade for budget conscious residential work. It delivers all the core benefits of synthetic at a price that makes the switch from felt affordable.

RoofLayer Standard is our most popular product. It offers stronger performance across every spec and is the go to choice for most residential and light commercial roofing jobs.

RoofLayer Premium is built for demanding conditions: metal roofs, steep slopes, extreme climates, and any project where maximum protection matters.

Frequently Asked Questions

What is the best roof underlayment for shingles? For most asphalt shingle roofs, a quality synthetic underlayment is the best choice. It provides superior water resistance, tear strength, and UV protection compared to felt. Pair it with ice and water shield at the eaves and valleys for complete protection.

How much does roof underlayment cost? Felt runs $20 to $30 per roll covering about 200 square feet. Synthetic runs $50 to $130 per roll covering 400 to 1,000 square feet. Per square foot, the cost difference between felt and synthetic is smaller than most people expect.

Can I install roof underlayment myself? Installation is straightforward. Start at the eave, roll out horizontally, overlap each row by at least 4 inches, and fasten with cap nails every 12 to 18 inches. That said, working on a roof involves fall risk, and professional installation ensures proper coverage and code compliance. Our roof underlayment installation guide walks through every step.

Does roof underlayment go over or under ice and water shield? Ice and water shield goes down first in the areas that need it (eaves, valleys, penetrations). Synthetic underlayment then covers the rest of the deck, overlapping onto the ice and water shield by at least 4 inches.

How long does roof underlayment last? Felt: 10 to 20 years. Synthetic: 25 to 40 years. Rubberized asphalt: up to 40 years. For the longest protection, synthetic or rubberized asphalt is the better investment.

Will my shingle warranty be voided without underlayment? Almost certainly yes. Major shingle manufacturers including Owens Corning and GAF require underlayment as part of their approved roofing system. Several now specifically require synthetic for full warranty coverage.

The Right Underlayment Pays for Itself

Roof underlayment is not the place to cut corners. The cost difference between felt and synthetic is a fraction of the total roofing project, but the difference in long term protection is significant. A quality synthetic underlayment keeps your deck dry, your warranty valid, and your roof performing for decades.

Ready to find the right product for your project? Call us at 877-540-5678 or visit bcpinc.us/roof-underlayment to compare our Eco, Standard, and Premium options.