For nearly every roof we install, synthetic underlayment is the better choice over traditional felt. It resists water more effectively, holds up far longer, lays flatter, and stands up to our western Pennsylvania weather in ways felt simply cannot. Felt still has its place and a lower price tag, but for lasting protection in the greater Pittsburgh climate, synthetic wins.
Since 1995 we have installed roofs across Irwin, the Norwin area, and Westmoreland County, and we have seen firsthand how the layer beneath your shingles affects how long a roof lasts. This guide compares synthetic and felt underlayment honestly so you understand what is going under your shingles and why it matters.
What Underlayment Does and Why It Matters
Underlayment is the protective barrier installed directly on your roof decking, underneath the shingles. Think of it as a second line of defense. When wind driven rain, ice dams, or a lifted shingle lets water past the top layer, the underlayment is what keeps that water from reaching the wood and your home’s interior.
In our freeze thaw climate, this backup layer earns its keep every winter. Ice dams form along the eaves, snow melts and refreezes, and water gets pushed under shingles where it never would in a milder region. A quality underlayment is not a place to cut corners on a Pittsburgh area roof.
Felt Underlayment: The Traditional Option
Felt, often called tar paper or roofing felt, is the traditional material roofers have used for generations. It is made from a paper or fiberglass base saturated with asphalt, and it comes in two common weights, 15 pound and the heavier, more durable 30 pound.
The Case for Felt
Felt’s main advantage is cost. It is less expensive per roll, which is why budget bids often rely on it. It has a long track record, and 30 pound felt offers reasonable protection when installed correctly. For a simple, lower budget project it can do the job.
The Drawbacks of Felt
Felt has real weaknesses. It absorbs water, so if it gets wet during installation or through a leak, it can wrinkle, tear, and lose effectiveness. It grows brittle over time, especially under the temperature swings we get here. It is heavier and tears more easily underfoot, and it can dry out and crack as it ages. Left exposed to sun and weather before shingles go on, felt degrades quickly.
Synthetic Underlayment: The Modern Standard
Synthetic underlayment is made from woven or spun polymers such as polypropylene or polyethylene. It was developed specifically to solve felt’s shortcomings, and it has become the standard for quality roof installations.
The Advantages of Synthetic
Synthetic underlayment resists water rather than absorbing it, so it keeps protecting even if it gets wet, and it will not wrinkle or rot. It is dramatically stronger and more tear resistant, which also makes it far safer for our crews to walk on. It is lightweight, lays flat and smooth for a better shingle surface, and holds up to sun exposure far longer than felt if a project spans several days. It also resists the temperature extremes and moisture that define our western Pennsylvania seasons. In short, it lasts longer and protects better.
The Trade Off
The main downside is cost. Synthetic underlayment is more expensive per square than felt. On a full roof, though, the difference is a modest share of the total project, and for the added decades of protection and peace of mind, we and most of our customers find it well worth it.
Synthetic vs Felt: Head to Head
Here is how the two stack up on the factors that matter most in our climate.
- Water resistance: Synthetic resists and sheds water. Felt absorbs it and can break down when wet.
- Durability: Synthetic is far stronger and more tear resistant. Felt grows brittle and tears more easily.
- Longevity: Synthetic holds up for the long haul. Felt ages, dries, and cracks faster.
- Weight and handling: Synthetic is lighter and lays flatter. Felt is heavier and harder to keep smooth.
- Sun exposure: Synthetic tolerates being exposed longer during a project. Felt degrades quickly in the sun.
- Cost: Felt is cheaper up front. Synthetic costs more but delivers more over the roof’s life.
For an independent, industry standard overview of roofing underlayment types and their performance, the National Roofing Contractors Association is a trusted reference.
Why We Use Synthetic in Our Climate
Our decision comes down to what western Pennsylvania throws at a roof. Between heavy snow, ice dams, driving rain, and constant freeze thaw cycles, the underlayment on an Irwin or Norwin roof works hard all winter. Synthetic gives your home a tougher, longer lasting second line of defense exactly where it is needed most.
We also pair synthetic underlayment with a self adhering ice and water shield in the valleys and along the eaves, the spots most prone to ice dams. That combination, installed over sound decking, is what makes a roof genuinely weather ready for our region. As an Owens Corning Platinum Preferred contractor, we install complete, certified roof systems that qualify for enhanced factory warranties, and the underlayment we choose is part of why those systems perform. You can see how every layer fits together on our roofing services page, and to understand how underlayment factors into your overall investment, see our guide to roof replacement cost in Pittsburgh.
The Bottom Line
Felt is not worthless, and on a tight budget it will function. But for a roof meant to protect your family for decades through Pittsburgh winters, synthetic underlayment is the smarter investment. It is one of those choices you make once and never think about again, which is exactly what you want from the layer beneath your shingles. Our roofing team is happy to walk you through the specific system we would recommend for your home.
Frequently Asked Questions
Is synthetic underlayment worth the extra cost?
For most homeowners in our climate, yes. Synthetic costs more per square than felt, but it is only a modest share of the total roof price and delivers far better water resistance, durability, and lifespan. Spread across the decades of protection it provides, the added cost is well worth it.
Can you install shingles over felt underlayment?
Yes, felt is a long established underlayment and shingles can absolutely go over it. The question is not whether it works but how well and for how long. In a demanding freeze thaw climate like ours, synthetic simply outperforms felt on nearly every measure that affects your roof’s lifespan.
Does underlayment stop all roof leaks?
Underlayment is a critical backup layer, not a cure all. It protects the decking when water gets past the shingles, but it works as part of a system that also includes proper flashing, ventilation, and an ice and water shield in vulnerable areas. All of these together are what keep a roof watertight.
What underlayment does Bella Construction use?
For nearly every roof we install, we use quality synthetic underlayment paired with a self adhering ice and water shield in the valleys and eaves. This combination stands up to western Pennsylvania weather and supports the enhanced warranties available through our Owens Corning Platinum Preferred certification. We will recommend the exact system that fits your home.
Ready for a Roof Built to Last?
If you want a roof that protects your family through every Pittsburgh winter, we would love to help. Bella Construction and Development offers free, no pressure roof inspections for homeowners across Irwin, the Norwin area, and greater Pittsburgh, and we will explain every layer of the system we recommend. Call 724.515.5163 to schedule your free inspection.