When you look at your roof, you only see the external finish, not the felt or synthetic roof underlayment underneath.

If you have a copper roof, you see large sheets of beautiful copper that give your home a sleek, clean look. If you have a clay tile roof, you see thick architectural tiles that add depth to your property. But, multiple layers make up a quality roofing system.

Underneath the finish, your roof has a layer of plywood sheathing, followed by underlayment. Underlayment provides protection between your roof’s finish and your home. Quality underlayment shields your home from the elements while adding years to your roof’s life.

You can choose different types of underlayment: traditional felt and synthetic plastic. Here’s what you should know about each.

What is Underlayment?

Your roof has three layers. The base layer, referred to as decking or sheathing, consists of sheets of thick plywood. These sheets give something for your underlayment and shingles to attach to and provide structural stability.

The external layer is your roof finish. When you chose your roof’s finish, you considered the aesthetic appeal and the functionality. You probably didn’t know that the long-term viability of your roof depends on the underlayment.

Underlayment serves as a type of membrane. It provides a layer of moisture resistance and ensures that the shingles, metal, or tile do not degrade the decking. While you don’t see your underlayment when you look at your roof, it is arguably the most important component.

What is Felt Roof Underlayment?

Traditional underlayment, a felt-like material, comes in 15- and 30-pound rolls. While 15-pound felt provides a more affordable option, it is prone to tearing, unlike its 30-pound counterpart.

The primary downside of felt is its weight. The finish on your roofing is heavy, and adding unneeded weight, such as 30-pound felt, adds to the load your home must support. Plus, traditional felt underlayment is expensive to repair.

What is Synthetic Roof Underlayment?

Instead of felt and fiberglass, synthetic underlayment is made of woven or spun polypropylene or polyethylene. Synthetic underlayment hit the market approximately 20 years ago and immediately provided roofing contractors with a lighter material that doesn’t sacrifice quality.

Is Synthetic Underlayment More Durable?

You want your contractor to use quality materials that will last for decades. Many homeowners only think of their roof’s finish, but it’s essential to pick a durable underlayment. Synthetic underlayment has a longer life expectancy than traditional fiberglass underlayment.

Standard felt underlayment can tear when faced with high winds and during installation. Even a tiny tear creates an opportunity for water to get into your home, where it can wreak havoc.

Synthetic underlayment is water-resistant and hard to tear. Fiberglass underlayment, on the other hand, absorbs water. In ideal situations, very little water reaches the underlayment, but your roofing finish can suffer damage if water gets in. The water resistance of synthetic underlayment makes it a superior option.

Synthetic underlayment also does a better job of holding roofing nails and screws, such as the type used in metal roofing. Providing a better grip for these fasteners helps ensure that water cannot leak around them.

Frequently Asked Questions (FAQ)FAQ

Is synthetic underlayment more expensive than fiberglass underlayment?

Felt or fiberglass underlayment costs approximately $5.00 per square foot. Synthetic underlayment costs around $7.00 per square foot. While synthetic fiberglass comes with a higher price tag, its durability makes it worth it.

Which type of underlayment is safer to work on?

Synthetic underlayment comes with a skid-proof finish, making it a safer option for roofing contractors. While it may seem like a minor factor, when contractors can move around on your roof with more ease, they can reduce the labor cost.

How long does synthetic underlayment last?

Most brands of synthetic underlayment come with a warranty ranging from 25 to 50 years. Felt underlayment lasts a maximum of 20 years.

Final Thoughts

Choosing the right type of underlayment adds years to the lifespan of your roof. A durable and lightweight product like synthetic underlayment lightens the load and creates a watertight seal.

Since traditional felt underlayment can be heavy and prone to rips, it’s no surprise that many homeowners choose synthetic underlayment.