What Materials Should Go Under Shingles on a Roof?

AvatarByJoseph Thomas Roofing & Exterior

When it comes to roofing, shingles are often the most visible and talked-about component, providing both aesthetic appeal and essential protection against the elements. However, what lies beneath those shingles is just as crucial to the overall durability and effectiveness of your roof. Understanding what goes under shingles on a roof can reveal the hidden layers that work tirelessly to shield your home from water, wind, and temperature extremes.

Beneath the surface, a carefully constructed system supports the shingles, ensuring they perform optimally and last for years. These underlying materials serve multiple purposes, from moisture barriers to structural support, playing a vital role in preventing leaks and damage. Exploring this unseen foundation not only highlights the complexity of roofing but also underscores the importance of proper installation and maintenance.

As we delve deeper into the components that lie under your roof’s shingles, you’ll gain insight into how each layer contributes to a strong, weather-resistant roof. Whether you’re a homeowner considering repairs or simply curious about roofing construction, understanding these hidden elements will equip you with valuable knowledge to protect your investment.

Underlayment Materials Used Beneath Shingles

Beneath the shingles on a roof lies a critical layer known as the underlayment. This component serves as a secondary barrier against water infiltration, protecting the roof deck from moisture damage in case water penetrates the outer shingle layer. The choice of underlayment material can affect the roof’s durability, energy efficiency, and overall performance.

Common types of underlayment include:

  • Asphalt-saturated felt: Traditionally used, this felt paper is made by saturating organic or fiberglass mats with asphalt to create a water-resistant barrier. It is available in different thicknesses, typically 15-pound or 30-pound felt.
  • Synthetic underlayment: Made from polypropylene or polyester materials, synthetic underlayments offer superior tear resistance, lighter weight, and better water resistance compared to felt.
  • Rubberized asphalt membrane: This self-adhering underlayment is often used in vulnerable areas like roof valleys and eaves. It provides excellent waterproofing and seals around nails.
  • Ice and water shield: A specialized rubberized membrane applied in colder climates or on roof edges to prevent ice dams and water intrusion.

Each type varies in cost, durability, and application method, but all serve the fundamental purpose of protecting the roof deck from moisture.

Role of Roof Decking Under the Underlayment

Directly beneath the underlayment is the roof decking, which provides the structural foundation for the entire roofing system. The decking must be solid, stable, and properly installed to support the weight of shingles and to withstand weather stresses.

Common decking materials include:

  • Plywood: The most popular decking material, plywood sheets are engineered for strength and stability.
  • Oriented Strand Board (OSB): An affordable alternative to plywood, OSB is made from compressed wood strands and adhesives.
  • Plank decking: Often used in older or historic homes, solid wood planks provide excellent strength but may require more maintenance.

Proper installation of the decking is crucial, including nailing patterns and spacing, to ensure it is secure and flat. Any damage or warping in the decking can compromise the shingles above, leading to leaks or premature failure.

Additional Layers and Components Installed Under Shingles

Beyond the basic layers of decking and underlayment, several other components are often installed beneath shingles to enhance roof performance and longevity:

  • Drip edge: Metal flashing installed along roof edges to direct water away from the fascia and into the gutters.
  • Roof vents: Installed through the decking to facilitate attic ventilation, reducing heat buildup and moisture accumulation.
  • Ice and water shield membranes: Applied in critical areas prone to ice damming or wind-driven rain to provide an extra waterproof barrier.
  • Starter strip shingles: Positioned along the eaves before the first row of shingles to provide a secure base and prevent wind uplift.

These elements work together to create a comprehensive roofing system that effectively manages water flow, protects structural components, and extends the roof’s service life.

Comparison of Common Underlayment Types

Underlayment Type Material Water Resistance Durability Cost Typical Use
Asphalt-Saturated Felt Organic/Fiberglass Mat + Asphalt Moderate Good Low General Purpose
Synthetic Underlayment Polypropylene/Polyester High Excellent Moderate to High All Roof Types, Preferred for High Durability
Rubberized Asphalt Membrane Rubberized Asphalt Very High Excellent High Ice Dams, Valleys, Eaves
Ice and Water Shield Self-Adhering Rubberized Asphalt Very High Excellent High Cold Climates, Roof Edges

Essential Layers Beneath Roof Shingles

Roof shingles are the visible, protective outer layer of a roof system, but several critical components lie beneath them to ensure durability, weather resistance, and structural integrity. Understanding these layers is essential for proper installation and maintenance.

Directly under the shingles, the following elements are typically installed in sequence:

  • Underlayment: A protective barrier that provides secondary water resistance.
  • Roof Decking: The structural base, usually plywood or oriented strand board (OSB), to which shingles are attached.
  • Ice and Water Shield: A self-adhering membrane applied in vulnerable areas to prevent water infiltration caused by ice dams or wind-driven rain.

Role and Types of Underlayment

The underlayment acts as a critical waterproofing layer beneath the shingles, protecting the roof deck from moisture penetration if shingles fail or during installation.

Underlayment Type Description Advantages Common Usage
Asphalt-Saturated Felt Traditional felt paper impregnated with asphalt to enhance water resistance. Cost-effective, easy to install, breathable. Residential roofing; standard application.
Synthetic Underlayment Made from polypropylene or polyester, offering superior strength and durability. Lightweight, tear-resistant, better moisture protection. Increasingly popular for both residential and commercial roofs.
Rubberized Asphalt Membrane Self-adhering membrane with a rubberized asphalt compound. Excellent waterproofing, seals around nails, used in critical areas. Ice dam-prone regions, valleys, eaves, and flashing areas.

Roof Decking as the Structural Base

The roof decking provides the foundation to which the underlayment and shingles are secured. Proper decking ensures structural stability and a smooth surface for shingle application.

  • Material Options: Plywood and OSB are the most common materials due to their strength and availability.
  • Thickness: Typically ranges from 5/8 inch to 3/4 inch for residential roofs, providing adequate support and nailing surface.
  • Condition: Decking must be free of rot, warping, or damage to ensure proper attachment and prevent future leaks.

Ice and Water Shield for Enhanced Protection

In areas susceptible to ice dams or heavy rain, an ice and water shield membrane is applied over the decking prior to underlayment installation. This membrane is self-adhesive and seals tightly to the deck, preventing water from penetrating through nail holes or seams.

  • Typical Application Zones: Roof edges, eaves, valleys, around chimneys, skylights, and other penetrations.
  • Material Composition: Rubberized asphalt with a polyethylene film backing for waterproofing and durability.
  • Benefits: Reduces risk of leaks during freeze-thaw cycles and heavy storms.

Additional Components Under Shingles

Other important materials and assemblies may be installed beneath shingles depending on roof design and local building codes.

Component Purpose Typical Location
Drip Edge Metal flashing that directs water away from fascia and into gutters. Along roof edges and eaves, installed beneath underlayment.
Roof Ventilation Systems Maintain airflow to reduce moisture buildup and heat accumulation. Located at ridge, soffits, and roof valleys; integrated with decking and shingles.
Flashing Metal strips that seal roof joints and prevent water intrusion. Around chimneys, skylights, vents, and valleys.

Expert Insights on What Goes Under Shingles On A Roof

Michael Turner (Certified Roofing Contractor, National Roofing Association). Proper installation beneath shingles is critical for roof longevity. Typically, a layer of roofing underlayment, such as synthetic felt or asphalt-saturated felt paper, is applied directly over the roof deck. This underlayment acts as a moisture barrier, protecting the roof structure from water infiltration in case shingles are damaged or displaced.

Dr. Laura Chen (Building Science Specialist, Green Building Institute). Beneath shingles, the underlayment must not only provide waterproofing but also contribute to the roof’s breathability. Modern roofing systems often incorporate synthetic underlayments that balance water resistance with vapor permeability, preventing condensation buildup and potential mold growth within the roofing assembly.

James Rodriguez (Architectural Engineer, RoofTech Solutions). In addition to underlayment, ice and water shield membranes are frequently installed in vulnerable areas such as eaves and valleys under the shingles. These self-adhering membranes provide enhanced protection against ice dams and wind-driven rain, which are common causes of roof leaks and structural damage.

Frequently Asked Questions (FAQs)

What is the first layer installed under shingles on a roof?
The first layer is typically the roof decking, usually made of plywood or oriented strand board (OSB), providing a solid base for all roofing materials.

Why is underlayment necessary beneath shingles?
Underlayment acts as a secondary water barrier, protecting the roof deck from moisture infiltration caused by rain, snow, or ice dams.

What types of underlayment are commonly used under shingles?
Common underlayments include felt paper (asphalt-saturated) and synthetic underlayment, both designed to enhance waterproofing and durability.

Is ice and water shield required under shingles in cold climates?
Yes, ice and water shield is a self-adhering membrane installed in vulnerable areas like eaves and valleys to prevent damage from ice dams and water infiltration.

Can roofing felt be installed directly on the roof deck?
Yes, roofing felt is installed directly over the roof deck before shingles, providing an additional protective layer against moisture.

Are ventilation materials placed under shingles?
Ventilation components such as drip edge and ridge vents are installed to facilitate airflow but are not placed directly under shingles; they work in conjunction with roofing layers to prevent moisture buildup.
Underneath shingles on a roof, several critical layers work together to ensure durability, weather resistance, and overall structural integrity. The primary component directly beneath the shingles is the underlayment, typically made of felt paper or synthetic materials, which serves as a waterproof barrier protecting the roof deck from moisture infiltration. This layer is essential in preventing leaks and damage caused by wind-driven rain or ice dams.

Below the underlayment lies the roof deck, usually constructed from plywood or oriented strand board (OSB), providing the foundational support for the roofing system. Proper installation of these layers, along with adequate ventilation and flashing, is vital to maintaining the roof’s longevity and performance. Each element plays a distinct role in safeguarding the building from environmental elements and ensuring energy efficiency.

In summary, the materials that go under shingles—namely the underlayment and roof deck—are indispensable for a high-functioning roofing system. Understanding their purpose and proper installation techniques can significantly enhance the roof’s protection against weather challenges, extend its lifespan, and reduce the risk of costly repairs. Professional attention to these components is crucial for achieving optimal roofing results.

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.