When adding metal roofs, having the right underlayment is as important as the metal panels you select. Underlayments are an integral part of metal roofs, providing a layer of protection against the elements and improving the roof’s longevity and performance.
Metal roof underlayment acts as a second line of defense against water damage, protecting it against leaks, condensation, and other problems that could hurt your roof’s performance. It’s not just about compliance with local building codes. It’s also key to ensuring the long-term integrity of the home.Â
What Is Roof Underlayment?
Metal roof underlayment is a protective layer roofers install between the roof deck and the metal roofing panels. It serves as a critical barrier against moisture, providing an extra layer of protection for the home.
Unlike roof sheathing or decking, which is the structural surface on which the roof is laid, underlayment is specifically designed to be water-resistant and enhance the roof’s overall performance.
This crucial component helps battle condensation that can form under metal panels, protecting the roof deck from damage. It also aids in managing the expansion and contraction of metal roofing materials because of temperature changes. Without an underlayment, expansion and contraction would lead to water seepage through seams and connections.
Why Is Metal Roof Underlayment Important?
Metal roof underlayments are important because of their overall protections and many elements, from water to noise to exterior temperatures.
Enhanced Protection Against the Elements
Underlayment provides an additional barrier against water infiltration. If your roof ever leaks, this extra layer can prevent water from reaching the roof deck and causing extensive damage to the home’s structure.
Condensation Management
Metal roofs are prone to condensation due to temperature differences between the interior and exterior of the home. Underlayment helps manage this moisture, preventing it from damaging the roof deck or leading to mold growth.
The absence of an underlayment exposes the roof decking to water damage, which eventually leads to mold buildup over time.Â
Thermal Regulation
Some types of underlayment can contribute to better thermal regulation in the home,‌ improving energy efficiency and comfort.
Noise Reduction
Metal roofs can create a lot of noise during rain or hailstorms. The right underlayment helps reduce this noise, making storms more tolerable and, at night, making sleep possible.
Extended Roof Lifespan
By protecting the roof deck from moisture and helping to manage the expansion and contraction of metal roofing materials, underlayment significantly extends the life of the entire roof.
Best Metal Roof Underlayment Options
When it comes to choosing the best underlayment for a metal roof, homeowners have several options. Each type has its own set of advantages and considerations. Here are the three main types of underlayment suitable for metal roofs:
Felt Underlayment
Also known as asphalt-saturated felt or felt paper, felt underlayment is a traditional option that has been used in roofing for many years.
Advantages:
- Affordable
- Readily available
- Provides adequate water resistance in most conditions
Disadvantages:
- Less durable than synthetic options
- Can wrinkle or tear during installation
- May deteriorate quickly if exposed to prolonged moisture
Felt underlayment is best for dry climates with low humidity levels. It’s available in 15-pound and 30-pound variants, with the latter being thicker and heavier. It is the most budget-friendly option. However, the product doesn’t offer the same level of protection as more modern alternatives — especially in areas prone to high moisture or extreme weather conditions.
Synthetic Underlayment
Made from polyethylene or polypropylene, synthetic underlayment is a more modern and increasingly popular choice for metal roofs.
Advantages:
- Highly durable and tear-resistant
- Lightweight and easy to install
- Excellent water resistance
- Mold and mildew-resistant
- Covers a larger area per roll compared to felt
Disadvantages:
- More expensive than felt underlayment
- Can require specific installation techniques
Synthetic underlayment is a wise choice for most climates and offers superior protection compared to felt. Its durability and ease of installation make it a favorite among roofing professionals. While the initial cost is higher, the long-term benefits often outweigh the price difference.
Self-Adhering Underlayment
Also known as peel-and-stick or rubberized asphalt underlayment, this option provides the highest level of water protection.
Advantages:
- Excellent waterproofing properties
- Creates a watertight seal with the roof deck
- Performs well in high-heat conditions
- Ideal for areas prone to ice dams or high winds
Disadvantages:
- Most expensive option
- Challenging to install, especially in cold weather
- No suitable for all types of roof decking
Roofers often use self-adhering underlayment in combination with other types — particularly in areas of the roof most prone to leaks, such as valleys, ridges, and around penetrations. Its strong waterproofing qualities make it an excellent choice for regions with severe weather conditions or homes in areas prone to ice dams.
Factors to Consider When Choosing Metal Roof Underlayment
Before you pick the underlayment for a metal roof, take into account your weather, your budget, the roof’s pitch, and a few other factors.
Climate and Weather Conditions
The local climate plays a significant role in determining the best underlayment. Areas with high rainfall, humidity, or extreme temperature fluctuations benefit from synthetic or self-adhering options.
Roof Pitch
Steeper roofs need more durable underlayment to withstand the increased stress and potential for water runoff.
Budget
While it’s tempting to opt for the least expensive option, investing in higher-quality underlayment can save money in the long run by preventing costly repairs.
Installation Complexity
Some underlayments are easier to install than others. Homeowners planning a DIY installation should consider their skill level and the complexity of the product.
Longevity
Consider how long the underlayment is expected to last. Higher-quality options may offer better long-term value despite higher initial costs.
Building Codes
Always check local building codes to ensure the chosen underlayment meets or exceeds requirements.
Installation Tips for Metal Roof Underlayment
Proper installation is crucial for the effectiveness of any underlayment. Here are six tips:
- Ensure the roof deck is clean, dry, and in good condition before installation.
- Start at the lowest point of the roof and work upward, overlapping each course according to the manufacturer’s specifications.
- Use appropriate fasteners and follow the recommended fastening pattern.
- Pay extra attention to areas around chimneys, vents, and valleys, using self-adhering underlayment in these vulnerable spots if possible.
- Allow for proper ventilation to prevent moisture buildup.
- Follow manufacturer guidelines for exposure time before installing the metal roofing panels.
Final Thoughts About Metal Roof Underlayment
Underlayment is a critical component of a durable and effective metal roof. While it’s not a visible part of a roof, I can’t overstate its importance. When you select the right underlayment ‌and hire professional roofers, you will significantly improve the performance and longevity of your metal roofs.
Whether opting for traditional felt, modern synthetic materials, or high-performance self-adhering products, the key is to match the underlayment to the needs of your home and local climate.
