Synthetic Roofing Underlayment: The Complete Buyer's Guide

Choosing the right roofing underlayment is one of the most important decisions in any roofing project. It is the layer you never see once the shingles go on, but it is working every day to protect your roof deck from moisture, wind driven rain, and weather damage.

Synthetic roofing underlayment has become the preferred choice for contractors, builders, and homeowners across the country. It outperforms traditional felt in nearly every category, from water resistance and tear strength to UV durability and installation speed.

If you are planning a roofing project and want to understand what synthetic underlayment is, how it works, and which product is right for your job, this guide covers everything you need to know.

What Is Synthetic Roofing Underlayment?

Synthetic roofing underlayment is a protective sheet made from engineered polypropylene or polyethylene polymers. It is installed directly on the roof deck (the plywood or OSB boards that form the base of your roof) before the shingles, tiles, or metal panels are laid on top.

Its primary job is to act as a secondary moisture barrier. If water ever gets past the shingles through wind damage, lifted tabs, or aging, the underlayment stops it from reaching the wood deck and the interior of your home.

Synthetic underlayment is made by weaving or spinning polymer fibers into a tough fabric, then coating it with additional polymers for water resistance and UV protection. The result is a material that is lighter, stronger, and far more durable than traditional asphalt saturated felt.

Why Contractors Are Switching to Synthetic

The construction industry has shifted heavily toward synthetic underlayment over the past decade. Here is why.

It does not absorb water. Felt soaks up moisture and can wrinkle, swell, and lose its protective ability when wet. Synthetic sheds water on contact and stays flat no matter how much rain hits it during installation.

It is dramatically stronger. Synthetic underlayment resists tearing from foot traffic, tools, and rough handling. On a busy roof with multiple workers, this matters. A torn underlayment is a compromised moisture barrier.

It covers more area per roll. A single roll of synthetic underlayment can cover 400 to 1,000 square feet depending on the product. A roll of 30 pound felt covers about 200 square feet. Fewer rolls means fewer trips up the ladder, fewer seams, and faster installation.

It handles UV exposure. If there is any delay between installing the underlayment and laying the shingles, synthetic can sit exposed for 60 to 180 days without breaking down. Felt starts to degrade within days of sun exposure.

It provides better traction. Most synthetic products have a textured or coated surface that gives workers better footing on the roof. This is a real safety advantage, especially on steep slopes.

It lasts longer. Under shingles, synthetic underlayment can last 25 to 40 years. Felt typically lasts 10 to 20 years. When you are installing a roof that should last 25 to 30 years, it makes no sense to put a 15 year underlayment underneath it.

Types of Synthetic Roofing Underlayment

Synthetic underlayment comes in different grades designed for different projects and budgets.

Economy Grade

Economy synthetic underlayment delivers the basic benefits of synthetic (water resistance, tear strength, UV protection) at a price point close to felt. It is a good fit for standard residential re-roofs in moderate climates where extreme weather is not a major concern.

BCP RoofLayer Eco is built for exactly this use case. It gives you the performance advantages of synthetic without stretching the budget on straightforward projects.

Standard Grade

Standard synthetic underlayment offers improved tear strength, better UV resistance (typically 90 to 120 days), and enhanced water shedding compared to economy products. It is the most popular choice among roofing contractors for everyday residential and light commercial work.

BCP RoofLayer Standard is our most used product. It handles a wide range of climates and roofing materials and installs quickly with its lightweight, lay flat design.

Premium Grade

Premium synthetic underlayment is built for demanding projects. It offers the highest tear strength, longest UV exposure ratings (up to 180 days or more), and superior water resistance. Premium products are the best choice for harsh climates, steep slope roofs, metal roofing applications, and projects where the roof deck may be exposed for extended periods.

BCP RoofLayer Premium delivers top tier performance for contractors who need an underlayment that can take whatever the job site throws at it.

How to Choose the Right Product

Picking the right synthetic underlayment comes down to four factors.

Your roofing material. Asphalt shingles work well with any grade of synthetic underlayment. Metal roofs need a product with higher heat resistance. Tile and slate roofs benefit from premium grade products with extra tear strength to handle the weight and rigidity of those materials.

Your climate. Hot, dry climates demand strong UV resistance. Cold, snowy climates need an underlayment paired with ice and water shield at the eaves and valleys. Wet, rainy regions need the highest water resistance available. We covered this in detail in our climate guide.

Your project timeline. If shingles will go on the same week the underlayment is installed, economy grade is fine. If there could be weeks or months of exposure, choose a product with a longer UV rating.

Your budget. Economy synthetic costs slightly more than felt but saves money through faster installation and fewer callbacks. Standard is the sweet spot for most projects. Premium is worth the investment on high value properties and demanding conditions.

Installation Basics

Synthetic roofing underlayment installs in the same general way as felt but with a few differences.

Start at the eave (the lowest edge of the roof) and roll the underlayment out horizontally across the deck. Fasten with cap nails or cap staples every 12 to 18 inches along the edges and every 24 inches in the field.

Each row should overlap the one below it by at least 4 inches on horizontal seams. End laps where two sheets meet along their short edges should overlap by at least 6 inches. Some manufacturers print alignment guides directly on the underlayment to make spacing consistent and easy.

In valleys and at the eaves, many roofers install ice and water shield first, then overlap the synthetic underlayment onto its edges. This combination gives you waterproof protection in the high risk zones and moisture resistant coverage across the rest of the deck.

For a more detailed walkthrough of roof underlayment installation, check out our dedicated guide.

Synthetic Underlayment and Shingle Warranties

This is a detail many homeowners overlook. Several major shingle manufacturers, including Owens Corning and GAF, now recommend or require synthetic underlayment for their warranty to remain valid.

If you install felt underlayment under shingles from a manufacturer that requires synthetic, you could void the warranty entirely. That means if your shingles fail prematurely, the manufacturer may deny your claim because the underlayment did not meet their specifications.

Always check the shingle manufacturer's installation requirements before choosing your underlayment. Using the right product protects your investment and keeps your warranty intact.

What Synthetic Underlayment Costs

Synthetic underlayment costs more per roll than felt, but covers more area and installs faster. Here is a general pricing breakdown.

Economy synthetic runs about $50 to $65 per roll, covering 400 to 1,000 square feet depending on the product. Standard grade costs about $65 to $90 per roll. Premium products range from $90 to $130 per roll.

By comparison, a roll of 30 pound felt costs about $20 to $30 but only covers about 200 square feet. When you calculate the cost per square foot of actual coverage, synthetic is often comparable to or only slightly more than felt. Factor in the faster installation time and the reduced risk of callbacks, and synthetic typically saves money on the total project cost.

Frequently Asked Questions

Is synthetic underlayment waterproof? Synthetic underlayment is highly water resistant and will shed rain effectively. However, it is not a fully sealed membrane like ice and water shield. For areas where standing water or ice dams are a concern, peel and stick underlayment is the better choice.

Can I use synthetic underlayment under any roofing material? Yes. Synthetic works well under asphalt shingles, metal roofing, tile, slate, and cedar shakes. Always verify compatibility with the specific roofing material manufacturer's installation guidelines.

How long can synthetic underlayment be exposed before shingles go on? It depends on the product. Economy grades typically handle 30 to 90 days. Standard and premium products can handle 90 to 180 days or more. Check the spec sheet for your specific product.

Do I still need ice and water shield if I use synthetic underlayment? Yes. Synthetic underlayment covers the main field of the roof, but ice and water shield should still be used at the eaves, in valleys, and around penetrations for full waterproof protection in those high risk areas.

Is synthetic underlayment worth the extra cost over felt? For most projects, yes. The longer lifespan, faster installation, better weather performance, and warranty compliance make synthetic the smarter long term investment. We covered this comparison in detail in our synthetic vs. felt guide.

Get the Right Underlayment for Your Roof

Synthetic roofing underlayment is the standard for modern roofing projects. It protects better, installs faster, and lasts longer than felt. Whether you are a contractor running jobs every week or a homeowner investing in a new roof, the underlayment you choose makes a real difference in how your roof performs over the next 30 years.

At BCP Inc., we offer a full lineup of synthetic roofing underlayment products designed for every project and every budget. From our RoofLayer Eco for cost effective residential work to our RoofLayer Premium for demanding commercial and high performance applications, we have the product that fits your job.

Ready to order? Call us at 877-540-5678 or visit bcpinc.us/roof-underlayment to compare products and request a quote.