Underlayment & Ventilation

Why is Roofing Underlayment & Venting Important?

In the Seattle area (where rain, wind, and moisture are a constant concern) proper roofing underlayment helps create a watertight barrier beneath your roof covering. And with the city’s mix of cold winters and warm summers, a well-ventilated roof is essential for controlling humidity, preventing mold, and improving energy efficiency.

Whether you're replacing a residential roof in Ballard or maintaining a commercial flat roof in SODO, understanding how these systems work—and choosing the right materials—will save you time, money, and frustration down the road.

What Is Roofing Underlayment?

Underlayment is a water-resistant or waterproof barrier that sits between your roof deck and the visible roofing material (like shingles or metal). It acts as a secondary defense against moisture, especially during heavy rain, snow, or wind-driven storms.

There are three common types of underlayment:

• Asphalt-saturated felt – Also known as “felt paper,” this traditional option offers basic protection and affordability.

• Synthetic underlayment – Lightweight, tear-resistant, and more durable than felt. A common choice for modern roofs.

• Rubberized asphalt – Self-adhering and waterproof, often used in vulnerable areas like eaves, valleys, and low-slope sections.

Why Underlayment Matters

• Moisture Protection: Prevents water from seeping into the roof deck.

• Improved Lifespan: Helps extend the life of your roofing materials.

• Code Compliance: Required in most residential and commercial building codes.

• Weather Backup: Offers temporary protection during installation or in case of material damage.

Our recommendation: Go with synthetic underlayment for most standard roof installs. It’s more durable, safer for installers to walk on, and holds up better in extreme weather. Use rubberized asphalt in high-risk areas for added protection.

The Role of Roof Ventilation

Roof ventilation helps regulate air flow in your attic or roof cavity. A well-ventilated roof lets hot air and moisture escape, reducing strain on your HVAC system and protecting your roof structure from rot, mold, and ice dams.

There are two main types of ventilation systems:

• Intake vents – Usually installed under the eaves or soffits to draw cool air into the attic.

• Exhaust vents – Placed near the roof ridge or gables to release hot, moist air.

Benefits of Proper Ventilation

• Temperature Control: Reduces heat buildup in summer.

• Moisture Prevention: Lowers risk of condensation and mold growth.

• Energy Efficiency: Helps your insulation work better and cuts down on cooling costs.

• Longer Roof Life: Prevents warping, cracking, and shingle damage caused by trapped heat and moisture.

Our recommendation: Use a balanced ventilation system—equal intake and exhaust—to keep air moving efficiently. Ridge vents paired with soffit vents are a great choice for most residential and low-slope commercial buildings.

Final Thoughts

Underlayment and ventilation may not be visible, but they’re essential to the performance and longevity of any roofing system. Choosing the right products and ensuring proper installation can save you thousands in repairs and energy costs down the line.

Have questions about what works best for your property? Get in touch—we’ll help you build a roof that lasts.