(440) 307-2060
What Goes Under Shingles on a Roof? A Complete Guide
When most homeowners think about a roof, they picture the visible surface—rows of shingles neatly overlapping across the house. But what goes under shingles on a roof is just as important as the shingles themselves. Beneath that finished surface lies a whole system of layers, each with its own job: keeping water out, protecting against wind, preventing leaks, and helping your roof last longer. Without these hidden components, shingles alone wouldn’t stand a chance against decades of rain, snow, heat, and storms.
In this guide, we’ll explore every layer under shingles, why each one matters, how they interact, and what homeowners should know when it comes time for repair or replacement.
Why Layers Under Shingles Matter
Shingles are the outer armor, but a roof isn’t just shingles nailed to wood. Underneath, a series of materials work together to:
- Protect against water infiltration
- Provide ventilation and insulation
- Stabilize the surface for shingles
- Add fire resistance and durability
- Manage heat and moisture flow inside the home
Think of it like clothing in winter: the shingles are your jacket, but without base layers, socks, and gloves, you wouldn’t be fully protected.
The Roofing System: An Overview
A modern roof system typically consists of:
- Roof deck (sheathing) – the structural foundation, usually plywood or OSB.
- Underlayment – a water-resistant or waterproof barrier.
- Ice and water shield – a protective membrane in vulnerable areas.
- Drip edge – metal flashing along eaves and rakes.
- Flashing – protective metal pieces around chimneys, vents, and valleys.
- Starter strips – the first row of shingles for wind resistance.
- Shingles – the final protective layer.
- Ventilation components – ridge vents, soffit vents, or gable vents.
Each piece has a role in the roof’s defense system. Let’s go through them one by one.
Roof Deck (Sheathing)
At the bottom of the system is the roof deck, sometimes called sheathing. This is the surface that everything else attaches to.
- Common materials: plywood or oriented strand board (OSB).
- Thickness: usually 7/16″ to 5/8″, depending on local codes.
- Function: provides structural stability and a nailing base for shingles.
If the deck is rotted, warped, or weakened, no amount of underlayment or shingles will make the roof strong. That’s why a good roofing job often starts with inspecting—and sometimes replacing—sections of sheathing.
Underlayment
Perhaps the most critical answer to “what goes under shingles on a roof” is the underlayment. This is a sheet material rolled out over the decking before shingles are nailed down.
Purpose:
- Provides a secondary barrier against water.
- Protects the deck from rain during installation.
- Improves fire resistance.
- Helps shingles lay flatter and more uniform.
Types of underlayment:
- Felt (tar paper)
- Traditional choice, made from paper or fiberglass saturated with asphalt.
- Comes in 15-pound or 30-pound rolls.
- More affordable, but can tear during installation.
- Synthetic underlayment
- Made of polyethylene or polypropylene.
- Lighter, stronger, more resistant to tearing.
- More slip-resistant for installers.
- Increasingly common in modern roofing.
- Rubberized asphalt membranes
- Self-adhesive and waterproof.
- Often used in combination with other underlayment.
Underlayment is like the unsung hero of roofing—it’s hidden, but it often saves the day when shingles are blown off or water sneaks beneath the outer layer.
Ice and Water Shield
In cold climates, ice dams are a major concern. When snow melts and refreezes at roof edges, water can back up under shingles. That’s where ice and water shield comes in.
- Material: a self-adhering membrane made of modified bitumen.
- Application: installed along eaves, valleys, and other vulnerable areas.
- Function: seals tightly around nails to prevent water leaks.
Even in warm regions, this material is sometimes used around chimneys, skylights, or valleys where water flow is concentrated.
Drip Edge
Along the edges of the roof, thin strips of metal called drip edge are installed before shingles.
- Purpose: directs water away from the fascia and into the gutters.
- Placement: runs along eaves and rakes, under starter shingles.
- Benefit: prevents water damage to wood trim and reduces rot.
Many older roofs don’t have drip edge, but modern building codes often require it.
Flashing
No roof is complete without flashing, the metal strips that seal transitions and penetrations.
- Where it’s used: around chimneys, skylights, dormers, plumbing vents, and valleys.
- Material: typically aluminum, galvanized steel, or copper.
- Function: prevents leaks where shingles can’t provide coverage alone.
Flashing is one of the most common leak points if it’s poorly installed or damaged.
Starter Strips
Before the first row of shingles is laid, starter strips are installed. These are specialized shingles or cut strips that:
- Provide extra adhesive along the roof edge.
- Help resist wind uplift.
- Ensure the first row is straight and secure.
Without starter strips, strong winds can easily peel shingles from the edge upward.
Ventilation Components
What goes under shingles on a roof isn’t only about moisture barriers—it’s also about airflow. Proper ventilation prevents heat buildup and condensation.
- Ridge vents: installed at the peak of the roof to allow hot air to escape.
- Soffit vents: located under eaves to let cooler air in.
- Gable vents: optional vents on gable walls.
Without good ventilation, shingles can age prematurely, insulation can get damp, and attic moisture can cause mold growth.
Attic Insulation and Vapor Barriers
Though technically inside the house, attic insulation plays a role in the roofing system. Vapor barriers and insulation:
- Reduce heat transfer.
- Prevent condensation on the underside of the roof deck.
- Improve energy efficiency.
A poorly insulated attic can cause ice dams, excessive energy bills, and even shorten roof lifespan.
Comparing Older Roofs vs. Modern Roof Systems
Fifty years ago, many roofs had fewer layers. Builders often skipped drip edge or ice barriers, relying on basic felt underlayment alone.
Modern codes and materials have raised expectations:
- Stronger synthetic underlayment.
- Widespread use of ice and water shield.
- Better flashing details.
- Improved ventilation designs.
This evolution means today’s roofs, while more expensive upfront, are more durable and resistant to leaks.
Common Mistakes in What Goes Under Shingles
- Skipping underlayment altogether – Sometimes done to cut costs, but it’s a recipe for leaks.
- Overlapping poorly – Underlayment must overlap correctly to shed water.
- Using staples instead of nails – Staples can tear through felt.
- Not sealing valleys properly – Valleys handle huge amounts of water flow.
- Improper ventilation – Without airflow, even the best materials fail early.
Regional Considerations
The right choices under shingles often depend on climate:
- Cold climates: Ice and water shield is essential. Ventilation is critical to prevent ice dams.
- Hot, dry climates: Synthetic underlayment resists heat better than felt.
- Windy coastal regions: Starter strips, drip edge, and strong underlayment adhesives are key.
- Rain-heavy climates: Extra flashing and water-resistant barriers help prevent leaks.
How Roofers Install the Layers
Step by step, a typical installation goes like this:
- Tear off old shingles and underlayment.
- Inspect and repair roof decking.
- Install drip edge along eaves.
- Roll out underlayment across the deck.
- Apply ice and water shield where needed.
- Install flashing around protrusions.
- Add starter strips at the bottom edge.
- Lay shingles row by row.
- Cap with ridge shingles and ventilation.
Each layer builds upon the previous one, creating a watertight system.
Lifespan and Replacement
Even though underlayment and membranes are hidden, they age just like shingles.
- Felt underlayment: may become brittle within 20 years.
- Synthetic underlayment: can last 40 years or more.
- Ice and water shield: typically lasts as long as the shingles above it.
When shingles are replaced, underlayment should also be updated—it’s not wise to reuse old layers under a new roof.
Cost of Materials Under Shingles
While shingles often make up the bulk of the cost, the materials beneath them contribute significantly:
- Underlayment: $0.15–$0.50 per square foot.
- Ice and water shield: $0.75–$1.50 per square foot in applied areas.
- Drip edge: $1–$3 per linear foot.
- Flashing: $8–$15 per piece (chimney flashing more).
- Starter strips: $0.80–$1.50 per linear foot.
On a 2,000-square-foot home, these layers can add several thousand dollars, but skipping them can lead to far costlier repairs.
Myths About What Goes Under Shingles
- “Shingles alone are waterproof.”
Wrong. Shingles shed water, but they’re not watertight. Underlayment is essential. - “All underlayments are the same.”
Not true—synthetics and membranes perform far better than basic felt. - “Ventilation doesn’t matter if shingles are high-quality.”
Even the best shingles fail early if the attic isn’t ventilated.
Future Innovations in Roofing Layers
Technology keeps evolving. Some upcoming improvements include:
- Self-healing underlayment that seals around nails even more effectively.
- Integrated radiant barriers that reflect heat in hot climates.
- Smarter ventilation systems that adjust to temperature and humidity.
These innovations may further extend roof life and efficiency in the decades ahead.
Putting It All Together
When you strip away the shingles, a roof is much more than meets the eye. Decking, underlayment, membranes, drip edges, flashing, ventilation, and starter strips all work in harmony to protect your home. Skipping any one of these can shorten roof life and lead to costly leaks.
So, what goes under shingles on a roof? The answer is a carefully engineered system designed to keep water out, regulate temperature, and ensure the shingles above can perform at their best. For homeowners, understanding these hidden layers makes you better prepared for conversations with contractors, inspections, or the next time your home needs a new roof.440-235-3124
