Understanding Roof Layers: What’s Under Your Shingles Matters

When most people think of a roof, they picture the shingles. While shingles are the outermost defense against the elements, they’re just one part of a much more complex system. A high-performing roof relies on several carefully installed layers that work together to protect your home from weather, regulate temperature, and keep moisture out. In this blog, we’ll take a closer look at the different components beneath your shingles—and why they matter.

1. Roof Decking (Sheathing)

What it is:
The foundation of your roof. Typically made of plywood or oriented strand board (OSB), decking provides the structural base for the rest of the roofing system.

Why it matters:

• Supports all other roofing materials
• Must be dry and stable to prevent sagging or rot
• Any deterioration here can lead to major structural issues

2. Ice and Water Shield

What it is:
A waterproof membrane installed in vulnerable areas like eaves, valleys, and around roof penetrations.

Why it matters:

• Prevents water intrusion from ice dams and wind-driven rain
• Adds extra protection beneath shingles
• Especially important in colder climates or regions with heavy storms

3. Underlayment

What it is:
A water-resistant or waterproof barrier installed over the decking and under the shingles. Common types include felt paper and synthetic underlayment.

Why it matters:

• Provides a secondary layer of protection from leaks
• Shields the decking from moisture
• Required by most building codes and manufacturer warranties

4. Drip Edge

What it is:
A metal flashing installed along the edges of the roof to direct water away from the fascia and into the gutters.

Why it matters:

• Protects the edges of your roof deck from water damage
• Prevents rain from getting under the shingles
• Helps improve overall roof drainage and lifespan

5. Starter Shingles

What it is:
The first course of shingles installed at the eaves and rakes to help secure the rest of the shingles.

Why it matters:

• Provides a secure, wind-resistant edge
• Seals off the roof’s lower edges to prevent leaks
• Helps the main field shingles lay properly and last longer

6. Shingles or Roofing Material

What it is:
The top layer—typically asphalt shingles, metal panels, tile, or slate—that provides the first line of defense against weather.

Why it matters:

• Protects all underlying layers from UV exposure, rain, hail, and wind
• Affects the curb appeal and style of your home
• Needs to be high-quality and properly installed for maximum performance

7. Flashing

What it is:
Thin metal strips installed around chimneys, vents, skylights, and valleys where two roof planes meet.

Why it matters:

• Seals joints and prevents water from seeping into vulnerable areas
• Essential for leak prevention
• Often a hidden culprit when roof leaks occur

8. Ridge Cap Shingles

What it is:
Special shingles installed at the peak (ridge) of your roof.

Why it matters:

• Provides a finished look
• Helps protect the roof’s most exposed seam
• Allows attic ventilation when installed with a ridge vent

9. Ventilation System

What it is:
Includes soffit vents, ridge vents, or attic fans that allow airflow through the attic.

Why it matters:

• Prevents moisture buildup and mold
• Regulates attic temperature
• Reduces strain on HVAC systems and extends shingle life

Why It All Matters Together

Each layer of your roof works as part of a system. If one component fails—like damaged underlayment or missing flashing—it can compromise the entire roof’s performance. That’s why quality materials and expert installation are key to a roof that lasts for decades.

How TM Roofing & Construction Group Ensures a Complete Roofing System

At TM Roofing & Construction Group, we go beyond shingles. Our team installs every component with precision—from decking to ventilation—so you get a fully protected, long-lasting roof that performs in every season.

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