The Anatomy of a Roof: What’s Under the Shingles?

When most people think of a roof, they picture the visible shingles. But there’s a lot more going on beneath the surface—and understanding what’s underneath your shingles can help you spot problems, plan for replacements, and hire the right contractor.

At Bella Construction, we believe in educating homeowners, not just selling them a service. Let’s take a closer look at the layers that make up a roof and why each one matters.

1. Roof Decking (or Sheathing)

This is the foundation of your entire roofing system. Roof decking is typically made of plywood or OSB (oriented strand board) and is attached directly to your home’s framing. It’s what all the other layers rest on.

👉 Why It Matters: If your roof decking is rotted, warped, or has large gaps (more than 1/4 inch between boards), it can compromise the entire roof. That’s why Bella Construction inspects and replaces damaged decking as part of every quality roof replacement.

2. Ice and Water Shield

Installed at the edges of the roof and in valleys, this is a waterproof membrane designed to prevent leaks caused by ice dams and wind-driven rain.

👉 Why It Matters: In places like Western PA, where snow and freezing temps are common, ice and water shield is your roof’s first defense against winter water damage.

3. Roofing Underlayment

This felt or synthetic layer covers the entire roof decking and acts as a secondary water barrier under the shingles.

👉 Why It Matters: If wind lifts or damages your shingles, underlayment helps prevent moisture from reaching the wood decking. High-quality underlayment also improves fire resistance and energy efficiency.

4. Starter Strip Shingles

Placed along the eaves and edges of the roof, starter shingles are critical for sealing the first row of shingles and preventing wind uplift.

👉 Why It Matters: A missing or poorly installed starter strip can cause shingles to lift, leak, or blow off—especially during Pittsburgh’s spring storms.

5. Asphalt Shingles (or Other Roofing Material)

Now we get to what everyone sees! Shingles come in a range of materials, but most homes in Western PA use architectural asphalt shingles because they’re durable, cost-effective, and come in a wide variety of colors and styles.

👉 Why It Matters: The shingles protect your home from UV rays, wind, and water—but only when properly nailed and layered. High nailing, for example, is a bad practice that voids manufacturer warranties and increases the risk of blow-off.

6. Ridge Cap Shingles and Vents

The ridge is the peak of your roof, and it’s often topped with special ridge cap shingles and ventilation systems to allow warm, moist air to escape from your attic.

👉 Why It Matters: A well-ventilated roof helps keep your home cooler in the summer and reduces the chance of moisture buildup and mold.

7. Flashing & Drip Edge

These metal components are installed along edges, chimneys, vents, and valleys to direct water away from vulnerable areas.

👉 Why It Matters: Flashing is your roof’s leak prevention MVP. Missing or improperly installed flashing is one of the top causes of roof leaks.

Your Roofing System is Just That—a System

A roof is more than just shingles—it’s a carefully layered system of protection. If one component fails, it can lead to major problems down the road, like leaks, rot, and energy loss.

That’s why at Bella Construction, we take the time to inspect every layer, from decking to ventilation, before and during your roof replacement.

Is Your Roof Doing Its Job?

Not sure what’s under your shingles? You don’t have to climb up there—we’ll do it for you. Schedule a free roof inspection with Bella Construction, and we’ll assess the full anatomy of your roof, explain any concerns, and give you honest advice you can trust.

📞 Call 724-515-5163
🌐 Visit www.mybellaroof.com to schedule your free consultation.

Bella Construction & Development
Your Trusted Roofing Contractor in Western PA for Over 30 Years