What Is Under Shingles? Complete Guide to Roof Layers

When most homeowners think about their roof, they picture the shingles — those visible, protective pieces that give your home its finished look.

But the truth is, your shingles are just the top layer of a much more complex roofing system.

If you’ve ever wondered, “what is under shingles?”, you’re not alone. Many homeowners don’t realize that several hidden layers work together beneath the shingles to protect their home from rain, wind, snow, and heat.

At State Restoration Services, we believe that understanding what’s under your shingles can help you make smarter decisions about maintenance, repairs, and replacements.

So, let’s peel back the layers — literally — and take a look at what makes up a strong, weatherproof roof.

So, What Is Under Shingles?

Underneath your shingles lies a combination of materials that form your roofing system. Each layer plays an important role in keeping your home dry, insulated, and structurally sound.

Here’s a quick breakdown of what is under shingles:

1. Roof Deck (Sheathing)

2. Roof Underlayment

3. Ice and Water Shield (in cold climates)

4. Roof Flashing

5. Drip Edge

6. Roof Ventilation System

Let’s explore each of these layers in more detail and see how they work together.

1. Roof Deck (or Roof Sheathing)

The roof deck is the base layer that sits directly on top of your home’s rafters or trusses.

It’s usually made from plywood or oriented strand board (OSB) — strong, flat panels that provide a solid foundation for the rest of your roofing system.

Why It’s Important:

• Provides structure and support for shingles and underlayment

• Holds roofing nails and fasteners in place

• Acts as a barrier between your attic and the outdoors

If the roof deck becomes damaged or rotten (often due to water leaks), it can compromise the entire roof. That’s why, during roof replacements, State Restoration Services always inspects and repairs the decking as needed before installing new shingles.

2. Roof Underlayment

Next comes the roof underlayment, which sits directly between the deck and the shingles.

This layer acts as a secondary barrier against water and moisture. Even if shingles get lifted by wind or damaged by hail, the underlayment helps prevent leaks from entering your home.

There are two main types of underlayment:

A. Felt Paper (Asphalt-Saturated Felt)

• The traditional, affordable option

• Provides decent protection

• Comes in 15-lb and 30-lb thicknesses

B. Synthetic Underlayment

• Made from engineered polymers

• More durable and tear-resistant than felt

• Resists water absorption and UV damage

• The preferred choice for modern roofing

At State Restoration Services, we typically use synthetic underlayment because it lasts longer, handles heat better, and provides superior water resistance compared to traditional felt.

3. Ice and Water Shield (in Cold or Wet Climates)

If you live in an area that experiences heavy rain, snow, or ice dams, then your roof likely includes an ice and water shield.

This self-adhesive membrane is installed along roof edges, valleys, and around penetrations (like chimneys and vents) where leaks are most likely to occur.

How It Works:

• Seals around nails and fasteners

• Prevents melting snow or ice from seeping into the decking

• Provides extra protection during extreme weather

Even though it’s not visible, this layer can make the difference between a dry attic and a costly ceiling leak in winter.

4. Roof Flashing

Flashing is one of the most critical — and often overlooked — parts of your roofing system.

It consists of thin metal strips, usually made from aluminum or galvanized steel, that are installed around vulnerable areas such as:

• Chimneys

• Skylights

• Roof valleys

• Vents and pipes

Purpose of Flashing:

Flashing acts like a waterproof seal, directing rainwater away from joints, seams, and openings where leaks could occur.

Without properly installed flashing, even the best shingles and underlayment can’t fully protect your home.

At State Restoration Services, we take extra care to ensure flashing is correctly positioned and sealed — because a small mistake here can lead to big water damage later.

5. Drip Edge

The drip edge is a thin strip of metal installed along the roof’s edges (eaves and rakes).

Many homeowners don’t even realize it exists, but it’s crucial for keeping your roof dry and stable.

What It Does:

• Directs water into the gutters, not behind them

• Protects the edge of the roof deck from rot

• Helps prevent pests from entering the roof structure

A properly installed drip edge improves water flow off your roof and extends the life of your shingles and decking.

6. Roof Ventilation System

While not technically “under the shingles,” roof ventilation is an essential part of the system that affects everything below it.

A well-ventilated roof includes intake vents (usually under the eaves) and exhaust vents (along the ridge).

Why Ventilation Matters:

• Regulates attic temperature

• Prevents heat buildup that can damage shingles

• Reduces moisture that leads to mold or rot

• Improves energy efficiency

At State Restoration Services, we always assess attic ventilation during roof installations or repairs. Proper airflow can make your roof last significantly longer and reduce cooling costs.

Why Knowing What’s Under Your Shingles Matters

Understanding what is under shingles helps homeowners appreciate that a roof isn’t just a single layer of protection — it’s a system of materials working together.

When any one of these layers fails, your home becomes vulnerable to leaks, rot, mold, and costly damage.

Here’s why it’s worth knowing:

• You’ll make informed decisions about roof replacements.

• You’ll better understand repair recommendations from contractors.

• You’ll recognize the importance of professional installation.

Think of it like this — your shingles are the armor, but the layers underneath are the shield and structure that make the armor effective.

Common Problems Under Shingles

Even the best shingles can’t perform if the layers beneath them are compromised.
Here are a few issues we often find during inspections:

• Rotten decking due to long-term leaks or poor ventilation.

• Torn underlayment caused by improper installation.

• Missing drip edge leading to water infiltration at roof edges.

• Rusty or missing flashing, allowing leaks around chimneys and vents.

These problems aren’t always visible from the ground, which is why professional roof inspections — like those offered by State Restoration Services — are so important.

Frequently Asked Questions

1. What is under shingles?
Under shingles, you’ll find layers such as the roof deck, underlayment, ice and water shield, flashing, and drip edge — all designed to protect your home from water and weather damage.

2. Can you replace shingles without replacing the underlayment?
Sometimes, yes — but if the underlayment is old or damaged, it’s best to replace it during re-roofing.

3. How long does roof underlayment last?
Felt underlayment lasts around 15–20 years, while synthetic underlayment can last up to 30 years.

4. Do all roofs have an ice and water shield?
Not all, but homes in colder or wetter climates should definitely have one installed for extra protection.

5. What happens if the roof decking is damaged?
Damaged or rotted decking must be replaced before installing new shingles, or your roof could fail prematurely.

6. Who can inspect what’s under my shingles?
Only trained professionals. State Restoration Services offers full roof inspections to check the condition of all roofing layers and components.

Why Choose State Restoration Services

At State Restoration Services, we don’t just replace shingles — we build complete roofing systems that last.

Homeowners trust us because we:

• Use only top-quality materials (like GAF roofing systems)

• Follow manufacturer-certified installation practices

• Inspect every layer for hidden damage

• Offer transparent estimates and long-term warranties

Your roof is more than shingles — and we make sure every part of it performs at its best.

Conclusion: There’s More to Your Roof Than Meets the Eye

Now you know the answer to “what is under shingles” — and why it matters.

Beneath those visible shingles lies a series of protective layers that keep your home safe, dry, and energy-efficient.

View our residential roofing page for more information, or book free inspection here.

If your roof is aging, leaking, or due for replacement, contact State Restoration Services today.
Our experts will inspect every layer — from shingles to sheathing — to ensure your home is fully protected from the elements.