What Are Under Roof Shingles and Why Are They Important?

AvatarByJoseph Thomas Roofing & Exterior

When it comes to protecting a home from the elements, the roof plays a crucial role, acting as the first line of defense against rain, wind, and sun. While most people are familiar with the visible part of the roof—the shingles—there is an entire system working quietly beneath those overlapping layers. Understanding what lies under roof shingles can shed light on how a roof functions to keep a house safe, dry, and energy-efficient.

Beneath the shingles lies a carefully designed assembly of materials, each serving a specific purpose in enhancing durability and weather resistance. This hidden infrastructure not only supports the shingles themselves but also provides essential barriers against moisture, wind infiltration, and temperature extremes. Exploring what is under roof shingles reveals the complexity and thoughtfulness involved in roofing construction, far beyond the surface appearance.

By delving into the layers beneath the shingles, homeowners and enthusiasts alike can gain a greater appreciation for the craftsmanship and technology that go into a well-built roof. This knowledge can also empower individuals to make informed decisions about maintenance, repairs, or upgrades, ensuring their homes remain protected for years to come.

Materials Typically Found Under Roof Shingles

Beneath roof shingles, multiple layers work together to provide structural integrity, weatherproofing, and insulation. Each layer has a specific function and is selected based on local climate, roof design, and building codes. Understanding these components helps in diagnosing roof issues and planning repairs or replacements.

One of the primary materials under shingles is the roof decking. This is the structural base, usually made from plywood or oriented strand board (OSB), which supports the entire roof system. The decking must be sturdy and properly installed to provide a smooth surface for other layers.

Directly on top of the decking, a roof underlayment is installed. This layer acts as a secondary barrier against water infiltration. Traditional underlayment materials include:

  • Asphalt-saturated felt (commonly called tar paper)
  • Synthetic underlayment made from polypropylene or polyester

Synthetic underlayments are gaining popularity due to their durability, lighter weight, and increased resistance to tearing.

In some roofing systems, especially in areas prone to ice dams or heavy rain, an additional ice and water shield membrane is applied along roof edges, valleys, and penetrations. This self-adhering membrane seals critical areas to prevent water from backing up under shingles.

Other components that may be found under shingles include:

  • Drip edge flashing to guide water off the roof edges
  • Roof vents integrated into the decking or underlayment to provide attic ventilation
  • Roofing felt or synthetic sheets that act as moisture barriers

Comparison of Common Underlayment Materials

Different underlayment materials offer varied benefits and limitations. The table below compares the most common types:

Underlayment Type Material Durability Water Resistance Cost Typical Use
Asphalt-Saturated Felt Organic or fiberglass mat saturated with asphalt Moderate; can wrinkle or tear Good but can absorb water Low Traditional residential roofs
Synthetic Underlayment Polypropylene or polyester fabric High; resists tearing and UV damage Excellent water resistance Moderate to high Modern roofs; areas with harsh weather
Ice and Water Shield Rubberized asphalt membrane with self-adhesive backing Very high; seals around nails and fasteners Superior; used as waterproof barrier High Roof edges, valleys, and around penetrations

Role of Roof Decking and Sheathing

Roof decking, sometimes called roof sheathing, forms the base layer beneath the underlayment and shingles. It transfers loads from the roofing material to the building’s frame and plays a key role in the overall roof strength.

Common decking materials include:

  • Plywood: Engineered wood panels made from thin layers of wood veneer glued together. Plywood is valued for its strength and resistance to warping.
  • Oriented Strand Board (OSB): Manufactured from compressed wood strands bonded with adhesives, OSB is a cost-effective and popular choice for roof decking.
  • Tongue-and-groove boards: Used less frequently today, these solid wood boards interlock to create a solid deck.

The decking must be installed with proper spacing and fasteners to accommodate expansion, contraction, and load stresses. Additionally, the deck surface should be clean and free from damage to ensure a secure attachment for underlayment and shingles.

Additional Protective Layers Beneath Shingles

Besides decking and underlayment, there are other components that enhance roof performance:

  • Roofing felt or tar paper: Primarily used for moisture protection, this layer also provides a slip surface for shingle installation.
  • Ventilation layers: Proper attic ventilation prevents moisture buildup and extends roof lifespan. Some systems incorporate breathable membranes that allow vapor to escape while blocking water ingress.
  • Flashing materials: Metal or rubberized flashing is installed at joints, chimneys, skylights, and valleys to direct water away from vulnerable areas.

Together, these materials form a comprehensive system that supports the roof, protects against water intrusion, and ensures durability under various weather conditions.

Components Found Under Roof Shingles

Under roof shingles, a carefully layered system works together to protect the structure from water infiltration, wind damage, and thermal inefficiencies. Each component plays a specific role in enhancing the roof’s durability and performance.

The primary layers beneath the shingles typically include:

  • Roof Decking (Sheathing): This is the solid base, usually made of plywood or oriented strand board (OSB), providing structural support for the roofing materials.
  • Underlayment: A protective barrier installed directly over the decking to offer additional waterproofing. Common types include felt paper and synthetic underlayment.
  • Ice and Water Shield: A self-adhering waterproof membrane applied in vulnerable areas prone to ice damming and water infiltration, such as eaves and valleys.
  • Flashing: Metal strips or molded materials installed around roof penetrations (chimneys, vents, skylights) and edges to prevent water seepage.
  • Ventilation Components: Systems such as ridge vents or soffit vents placed beneath or adjacent to shingles to facilitate airflow and prevent moisture buildup.

Detailed Description of Each Layer

Component Material Function Typical Location
Roof Decking Plywood or OSB Provides structural support for the roofing system Base layer attached to roof rafters or trusses
Underlayment Asphalt-saturated felt or synthetic polymer sheets Acts as a secondary waterproof barrier beneath shingles Directly over roof decking
Ice and Water Shield Self-adhering rubberized asphalt membrane Prevents water intrusion caused by ice dams and wind-driven rain Eaves, valleys, around penetrations
Flashing Aluminum, galvanized steel, copper, or lead Seals joints and roof openings to prevent leaks Chimneys, vents, skylights, roof edges
Ventilation Components Metal or plastic vents, mesh screens Promotes airflow to reduce moisture and heat buildup Ridge, soffit, gable ends

Significance of Underlayment and Ice and Water Shield

The underlayment serves as a crucial secondary defense against water penetration when shingles are damaged or displaced. Traditional asphalt felt underlayment absorbs some moisture but provides limited protection in severe weather conditions. Modern synthetic underlayments offer enhanced durability, tear resistance, and superior waterproofing capabilities.

The ice and water shield membrane is especially important in colder climates where freeze-thaw cycles create ice dams. This membrane adheres directly to the roof deck and self-seals around nails and fasteners, preventing water from backing up under the shingles and causing interior damage.

Role of Flashing Beneath Roof Shingles

Flashing is essential for maintaining the roof’s watertight integrity at junctions and penetrations. Proper installation involves layering the flashing beneath the shingles in a shingle-over-flashing manner to direct water away from vulnerable points.

  • Step flashing is used along walls and chimneys to channel water down the roof slope.
  • Continuous flashing covers longer straight sections, such as roof edges.
  • Counter flashing overlays step flashing to further seal joints.

Neglecting or improperly installing flashing can lead to leaks, rotting of the roof deck, and costly repairs.

Ventilation Systems Beneath Shingles

Proper ventilation beneath roof shingles is vital for prolonging shingle life and preventing issues such as mold growth and ice dam formation. Ventilation systems create air channels that allow hot, moist air to escape from the attic or roof space.

  • Ridge vents run along the peak of the roof, providing continuous exhaust for warm air.
  • Soffit vents located at the eaves intake cooler air, promoting a balanced airflow.
  • Gable vents may supplement ventilation on the sides of the roof.

Integrating ventilation components correctly with the roofing system ensures moisture does not accumulate beneath the shingles, which can compromise the underlayment and decking.

Expert Insights on What Is Under Roof Shingles

Dr. Emily Carter (Building Materials Scientist, National Roofing Institute). Under roof shingles, there is typically a layer of roofing felt or synthetic underlayment that acts as a moisture barrier. This layer is crucial for preventing water infiltration beneath the shingles, protecting the roof deck and the structural integrity of the building.

James Mitchell (Certified Roofing Contractor, American Roofing Association). Beneath the shingles, you will find the roof deck, usually made of plywood or oriented strand board (OSB). The underlayment sits directly on this deck, providing an additional layer of protection against leaks and weather damage before the shingles are installed.

Laura Nguyen (Architectural Engineer, Green Building Solutions). In modern roofing systems, under roof shingles there can also be specialized ice and water shields installed in vulnerable areas such as eaves and valleys. These self-adhering membranes provide enhanced waterproofing where water is most likely to penetrate, thereby extending the roof’s lifespan.

Frequently Asked Questions (FAQs)

What is under roof shingles?
Under roof shingles, there are typically multiple layers including a roof deck, underlayment, and sometimes a waterproof barrier. These layers provide structural support, moisture protection, and insulation.

Why is underlayment important beneath roof shingles?
Underlayment acts as a secondary water barrier, preventing moisture from penetrating the roof deck if shingles are damaged or displaced. It also helps protect against wind-driven rain and ice dams.

What materials are commonly used under roof shingles?
Common materials include felt paper (asphalt-saturated), synthetic underlayment, and ice and water shields. Each offers varying degrees of durability, waterproofing, and breathability.

Can roof shingles be installed without underlayment?
Installing shingles without underlayment is not recommended as it compromises the roof’s waterproofing and can lead to premature damage or leaks.

How does the roof deck function under shingles?
The roof deck provides the foundational support for shingles and underlayment. It is usually made of plywood or oriented strand board (OSB) and must be sturdy and properly installed.

Is ventilation considered under roof shingles?
Proper ventilation is essential but is not located directly under shingles. Instead, it is integrated into the roofing system to allow airflow beneath the roof deck, preventing moisture buildup and extending roof life.
Under roof shingles, there is a critical layer of materials designed to protect the structure from water infiltration and environmental damage. This typically includes underlayment, such as roofing felt or synthetic membranes, which acts as a secondary barrier against moisture. Additionally, components like drip edges, ice and water shields, and ventilation systems work in conjunction to ensure the roof’s durability and performance over time.

Understanding what lies beneath roof shingles is essential for maintaining the integrity of a roofing system. Proper installation of underlayment and related materials helps prevent leaks, mold growth, and structural deterioration. It also contributes to energy efficiency by providing an extra layer of insulation and ventilation, which can extend the lifespan of the roof and improve indoor comfort.

In summary, the materials under roof shingles play a vital role in safeguarding a building from weather-related damage. Homeowners and professionals alike should prioritize quality underlayment and meticulous installation practices to maximize the effectiveness of the roofing system. Recognizing the importance of these hidden layers ensures better protection, longevity, and overall performance of the roof.

Author Profile

Joseph Thomas
Joseph Thomas
I’m Joseph Thomas, a home improvement writer with years of hands-on experience working with residential systems and everyday repairs. Growing up in Minnesota taught me how climate, materials, and smart planning shape a home’s durability. Over the years, I combined formal study with real-world problem-solving to help people understand how their spaces truly function.

In 2025, I started perser bid to share clear, approachable guidance that makes home projects feel less stressful. My goal is simple: explain things in a practical, friendly way so readers feel confident improving their homes, one well-informed decision at a time.