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What to Put Under Shingles: A Complete Guide to Roofing Underlayment
When it comes to roofing, most homeowners focus on the shingles—the visible layer that protects the home from rain, wind, and sun. However, what goes under shingles is just as critical to the roof’s durability, weather resistance, and overall performance.
If you’ve ever asked, “What do you put under shingles?” or wondered why underlayment is so important, you’ve come to the right place. This comprehensive guide covers everything you need to know about roofing underlayment: types, functions, installation tips, and how to choose the right material for your project.
Table of Contents
- Why Is Something Put Under Shingles?
- What Is Roofing Underlayment?
- Types of Underlayment Used Under Shingles
- Benefits of Using Underlayment Under Shingles
- How to Choose the Right Underlayment for Your Roof
- Installation Process of Underlayment Under Shingles
- Common Mistakes to Avoid When Installing Underlayment
- How Underlayment Works with Different Shingle Types
- Special Underlayment Requirements in Different Climates
- Cost Considerations: How Much Does Underlayment Add to Roofing Costs?
- Frequently Asked Questions (FAQs)
- Conclusion
1. Why Is Something Put Under Shingles?
Shingles are your roof’s first line of defense against the elements, but they aren’t a perfect waterproof barrier by themselves. Roofing underlayment serves as a protective layer installed directly over the roof deck and beneath the shingles. Here’s why it’s essential:
- Water Barrier: Acts as a secondary shield if water gets past the shingles.
- Protection from Wind-Driven Rain: Prevents moisture from penetrating roof decking.
- Vapor Barrier: Helps reduce condensation and moisture buildup inside the roof structure.
- Fire Resistance: Some underlayments add fire-resistant properties.
- Improved Roof Longevity: Extends the life of your shingles by providing stable and secure backing.
2. What Is Roofing Underlayment?
Roofing underlayment is a thin, protective layer placed between the roof deck (usually plywood or OSB) and the shingles. It is designed to protect the roof structure from moisture, prevent leaks, and improve overall roof performance.
Common Materials for Underlayment
- Felt Paper (Asphalt-saturated felt)
- Synthetic Underlayment
- Rubberized Asphalt Membrane
3. Types of Underlayment Used Under Shingles
3.1 Asphalt-Saturated Felt Paper
One of the most traditional and widely used roofing underlayments.
- Material: Fiberglass or organic mat saturated with asphalt.
- Thickness: Usually 15-pound or 30-pound felt.
- Pros: Affordable, easy to install, provides basic water resistance.
- Cons: Less durable than synthetic options, susceptible to tearing and mildew.
3.2 Synthetic Underlayment
Made from polypropylene or polyethylene materials.
- Pros: Lightweight, tear-resistant, breathable, resistant to UV damage.
- Cons: Typically more expensive than felt paper.
3.3 Rubberized Asphalt Membrane
Self-adhering membrane with a rubberized asphalt adhesive.
- Pros: Superior waterproofing, excellent for vulnerable areas like roof valleys and eaves, ice dams.
- Cons: Costlier and requires careful installation.
3.4 Peel-and-Stick Underlayment
This type adheres directly to the roof deck and forms a waterproof barrier.
- Uses: Common in ice dam-prone regions and critical areas.
4. Benefits of Using Underlayment Under Shingles
- Leak Protection: Provides backup waterproofing if shingles fail or are damaged.
- Roof Deck Protection: Shields the decking from moisture that can cause rot and deterioration.
- Improved Wind Resistance: Helps keep shingles in place during high winds.
- Mold and Mildew Prevention: Reduces chances of fungal growth caused by trapped moisture.
- Added Insulation: Some synthetic underlayments add a slight insulating effect.
- Code Compliance: Many building codes require underlayment for shingle roofs.
5. How to Choose the Right Underlayment for Your Roof
Consider Your Climate
- Wet or Snowy Climates: Rubberized asphalt membranes or peel-and-stick underlayment for better waterproofing.
- Hot and Dry Climates: Synthetic underlayment for UV resistance.
- Moderate Climates: Felt paper can be adequate if budget is a concern.
Roof Pitch and Design
- Steep slopes can use standard underlayment options.
- Low-slope roofs may require special membranes.
Budget
- Felt paper is the most affordable.
- Synthetic and rubberized membranes cost more but offer superior protection.
Compatibility with Shingles
- Ensure the underlayment is approved for use with your shingle type by the manufacturer.
6. Installation Process of Underlayment Under Shingles
Step 1: Prepare the Roof Deck
- Ensure the roof decking is clean, dry, and free of damage.
Step 2: Start at the Eaves
- Begin laying the underlayment at the roof’s eaves (lowest edge), overlapping the layers to ensure water runs off properly.
Step 3: Secure the Underlayment
- Use roofing nails or staples, following manufacturer guidelines.
- Ensure tight, wrinkle-free installation.
Step 4: Overlap Layers Properly
- Overlap horizontal and vertical seams as recommended to prevent leaks.
Step 5: Install Special Membranes in Vulnerable Areas
- Use rubberized or peel-and-stick membranes around chimneys, valleys, skylights, and eaves.
Step 6: Inspect Before Installing Shingles
- Make sure the underlayment is smooth, secure, and properly overlapped.
7. Common Mistakes to Avoid When Installing Underlayment
- Not Overlapping Layers Correctly: This can cause water infiltration.
- Using Incorrect Fasteners: Nails that are too short or inappropriate can fail.
- Installing Over Wet Decking: Moisture trapped under underlayment can cause problems.
- Ignoring Roof Valleys and Penetrations: These areas need extra waterproofing.
- Leaving Underlayment Exposed for Too Long: UV rays degrade some underlayments quickly.
8. How Underlayment Works with Different Shingle Types
Asphalt Shingles
- Require a water-resistant underlayment, typically felt or synthetic.
Wood Shingles or Shakes
- Often require breathable underlayment to prevent moisture buildup.
Metal Roofing (when installed over shingles)
- Underlayment can serve as a slip sheet and additional moisture barrier.
Tile Roofing
- May require specialized underlayment designed for heavy tiles and water protection.
9. Special Underlayment Requirements in Different Climates
Cold Climates
- Use ice and water shield membranes to prevent damage from ice dams.
- Ensure proper ventilation to reduce condensation.
Hot Climates
- Choose synthetic underlayments that resist UV degradation.
- Consider underlayments that help reflect heat.
Wet Climates
- Waterproof membranes and proper flashing are critical.
- Regular roof inspections to identify damage.
10. Cost Considerations: How Much Does Underlayment Add to Roofing Costs?
- Felt paper: Approximately $0.10 to $0.50 per square foot.
- Synthetic underlayment: $0.40 to $0.90 per square foot.
- Rubberized membranes: $0.75 to $1.50 per square foot.
- Installation labor adds to the overall cost but is essential for proper protection.
11. Frequently Asked Questions (FAQs)
Q: Can I install shingles without underlayment?
A: While it’s physically possible, it’s not recommended and often against building codes. Underlayment is crucial for preventing leaks.
Q: How long does roofing underlayment last?
A: Felt paper can last 15-20 years; synthetic materials may last longer, especially under shingles.
Q: Does underlayment improve energy efficiency?
A: Some synthetic underlayments offer slight insulating benefits, but the primary function is waterproofing.
Q: Can I install synthetic underlayment over old felt paper?
A: It’s generally best to remove old underlayment before installing a new one to ensure proper adhesion and performance.
12. Conclusion
Knowing what to put under shingles is vital for anyone planning a roofing project. The underlayment acts as a silent but essential guardian beneath your shingles, protecting your home from water damage, wind, and weather challenges. Whether you opt for traditional felt paper, modern synthetic materials, or rubberized membranes, choosing the right underlayment and installing it correctly ensures your roof’s longevity and performance.
Invest in quality materials and professional installation to keep your roof strong, dry, and protected for decades to come.
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