(440) 307-2060
What Do You Put Under Shingles? The Complete Guide to Roof Underlayment
When a roof is installed, what do you put under shingles ? r. Beneath them lies a critical component called underlayment. Although often overlooked, underlayment plays a vital role in protecting your home. Let’s explore what it is, why it’s essential, the differences between types, and how to choose the right one.
1. What Is Roof Underlayment?
Underlayment is a layer of material installed directly over the roof sheathing (like plywood or OSB), which sits beneath the shingles. Its functions include:
- Serving as a secondary water barrier if water gets past the shingles
- Protecting against ice dams, wind-driven rain, and leaks
- Smoothing out minor imperfections in the decking and hiding old nail holes
- Supporting certain fire-resistance ratings
- Offering temporary protection during installation before shingles are applied
It’s the insurance layer—roles go unnoticed unless you need it most.
2. Main Types of Underlayment
There are three primary types used under shingle roofs today:
a) Asphalt-Saturated Felt (Traditional Felt)
- Also known as felt paper or tar paper
- Made of organic or fiberglass fibers saturated with asphalt
- Comes in two weights: No. 15 (lighter) and No. 30 (thicker and more durable)
- Cost-effective and widely available
- Offers moderate water resistance but can absorb moisture and tear more easily
Best used in moderate climates or as a budget option.
b) Synthetic Underlayment
- Made from polypropylene or polyethylene polymers
- Lightweight and tear-resistant, with a slip-resistant surface
- Repels water and resists mold, and holds fasteners securely
- Easy to install and lasts longer than felt
Widely regarded by contractors as an upgrade in performance—even worth the slightly higher cost.
c) Rubberized Asphalt (Self-Adhered)
- Premium option, often used in critical roof areas like valleys, eaves, and skylights
- Has a sticky backing that self-seals around nails and edges
- Provides top-tier waterproofing and flexibility in extreme temperatures
Ideal in climates prone to ice dams or heavy rainfall, though more expensive and trickier to install.
3. Choosing the Right Underlayment
Several factors should guide your choice:
Climate
- Cold or wet climates: Rubberized asphalt helps prevent leaks
- High-wind or mold-prone areas: Synthetic underlayment’s strength and moisture resistance perform well
- Stable, mild climates: Quality felt can suffice on a budget
Roof Design
- Low-slope roofs: Benefit from self-adhering underlayment to prevent slips
- Steep roofs: Synthetic sheets are lightweight and easier to work with
Cost vs. Value
- Felt underlayment: Least expensive but shorter service life
- Synthetic: Balanced choice—longer durability with reasonable cost
- Rubberized asphalt: Best protection, best life, best cost if budget allows
Impact & Seasonal Exposure
- If your roof is going to be exposed before shingles go on, choose an underlayment with UV resistance—synthetics often handle that better.
Warranties and Requirements
- Some shingle manufacturers require synthetic underlayment to maintain roof warranties. Double-check for compatibility.
4. Real-World Feedback from Roofers
Contractors often share that synthetic underlayment:
- Resists tearing and wind damage better than felt
- Helps prevent moisture-related decking damage
- Makes installation safer and faster thanks to non-slip surfaces
Several professionals warn: using felt instead of synthetic can delay or void the warranty on premium shingle systems—always verify manufacturer requirements.
5. Installation Basics
A typical underlayment installation involves:
- Laying a drip edge along eaves or rake edges
- Rolling out the underlayment horizontally, overlapping seams properly:
- Felt: ~2 inches on steep slopes; ~19 inches on low slopes
- Synthetic: follow manufacturer’s overlap recommendations
- Fastening with nails, staples, or adhesive depending on the type
- Installing extra protection (like rubberized asphalt) around vulnerable areas (roof edges, valleys, and protrusions)
Each material has manufacturer-specific best practices—follow them closely for best performance.
6. Hidden Benefits You Might Not Know
Beyond moisture control, underlayment helps:
- Protect during the installation process or if a storm hits during work
- Prevent granule abrasion from decking imperfections
- Improve fire protection as needed by building codes
It’s a small investment that pays dividends in roof longevity.
7. When Underlayment Fails or Needs Replacement
Watch for these indicators that your underlayment—or overall roofing system—needs attention:
- Leaks that appear underneath roof sheathing or attic walls
- Soft or dark wood beneath shingles
- Shingles that feel loose because the surface underneath is degraded
- Discoloration or sagging underlayment visible along roof edges
In such cases, underlayment—or the entire roof system—may need repair or replacement.
8. Final Thoughts
Here’s a quick summary:
- Underlayment protects the roof deck and supports shingle performance
- Felt is affordable but less durable
- Synthetic offers strong protection and easier installation
- Self-adhering rubberized is even more robust, ideal for leak-prone zones
- Choose based on climate, slope, budget, and warranty requirements
Considering the importance of underlayment, investing in a quality option—especially synthetic or rubberized—can extend roof life and peace of mind.
Need help choosing the best option for your roof type or region? I can help you sort through options tailored to your home.(440)235-3124
