How to Choose the Right Underlayment for Your Metal Roof
Underlayment protects your roof from leaks and damage. Discover the main types, pros and cons, and how to pick the right one for your project.
When homeowners think about what materials they want for their metal roof, they often picture the visible parts of the system, like the type of panels or the color of the paint. But every part of a roofing system is integral to making sure it functions as it should, and even the parts of the roof that you don’t see – like the underlayment – are essential pieces worth consideration.
In this article, we’ll talk about what underlayment is, why it’s important, and how to choose the right underlayment product for your metal roof.
What Is Roofing Underlayment?
Roofing underlayment is a layer of material that’s installed between the roof’s decking and its surface layer. Its main purpose is to keep water from penetrating past the top layer into the decking. Essentially, it’s an added layer of protection that defends against leaking.
Even with standing seam systems, which offer superior protection, it’s important to have underlayment because it gives you that added backup when roofs face stress from age or severe weather. Underlayment provides a few advantages, including:
- Extends the life of the roofing system
- Provides added defense in case of leaks
- Ensures roofing assemblies are code-compliant and covered under warranty
Types of Roof Underlayment for Metal Roofs
1. Felt Paper or Tar Paper
- What it is: The traditional underlayment option, available in 15 lb. or 30 lb. rolls.
- Downsides: Can stick to the back of metal panels, tear over time, and doesn’t perform as well as modern products.
- Verdict: Though still used for shingle roofs, felt paper is not recommended for most of today’s metal roofing systems.
2. Synthetic
- What it is: A modern, mechanically-attached alternative to felt paper.
- Strengths: Lightweight, durable, and resistant to tearing.
- Limitations: Not waterproof – only sheds water. Must be installed on sloped roofs because laps aren’t sealed.
3. Self-Adhered (Peel & Stick, Ice & Water Shield)
- What it is: A synthetic underlayment with an adhesive backing.
- Strengths: Fully adhered to the decking, seals around nails, highly water-resistant.
- Best Uses: Entire roofs or high-risk areas like valleys, eaves, ridges and gables
4. Fire-Rated Self-Adhered Underlayment
- What it is: A peel & stick product engineered to improve fire resistance.
- Strengths: Can raise a roofing assembly to a Class A fire rating.
- Best Uses: Areas where building codes or insurance require enhanced fire protection or wildfire-prone areas.
How to Choose the Right Underlayment for a Metal Roof
Avoid Outdated Options
While some options like felt paper may look attractive because of their low price points, they shouldn’t be used on modern metal roofing systems. Roofing systems like standing seam have lifespans that can stretch fifty years or more. You want a product that will last as long as your assembly, and that means investing in something more durable than felt paper underlayment.
Match to Your Unique Roof
Every roof is different, depending on your region, the design, and the panel system. Be sure to look at the details of your specific project and key factors, like:
- Regional weather: If you live in areas with severe weather like hurricanes, high winds, and heavy rains, consider getting a self-adhered underlayment to ensure your system is protected.
- Temperature: Not all types of underlayment can handle extreme temperatures the same – be sure to find a type that will be able to withstand the extremes of your region.
- Roof slope: Steeper roofs may be able to get away with synthetic underlayment, while roofs with many valleys and ridges should look into peel & stick.
Consider Combining Different Types of Underlayment
Many projects take a hybrid approach to underlayment: synthetic on the main portions of the roof and peel & stick for the more vulnerable flashing zones such as eaves, valleys, headwalls, and sidewalls. This helps keep costs down while giving your roof added protection in areas most prone to leaking.
Ask Questions
Don’t be afraid to ask your contractor questions about the underlayment they plan to use or the best strategy for tackling your roof’s unique design. The more you know about roofing underlayment going in, the better questions you’ll be able to ask. Here’s a few free resources that dig deeper into types of underlayment and their uses:
Synthetic vs. Felt Underlayment for Metal Roofing: Which Is Best?
The 6 Best Synthetic Underlayment Manufacturers for Metal Roofing
Titanium® FR: Class A Fire-Rated Underlayment for Metal Roofs – Sheffield Metals
Compare Brands
Popular roofing underlayment brands include Owens Corning, Sharkskin, and many others. With hundreds of products available, it’s best to:
- Check compatibility: Make sure the underlayment is approved for your roof type and the slope.
- Rely on contractor experience: Contractors will likely have a brand they trust for safety, availability, and warranties.
- Balance cost versus performance: The best option might not be the cheapest, but it doesn’t have to be the most expensive.
- Look for preferred brands recommended by your metal roof manufacturer: if you’re unsure about what brand to use, ask your metal roofing manufacturer – they should have a list of preferred brands.
Look at Pricing
Pricing for roofing underlayment can be tricky. Roll sizes vary, so compare the cost per square foot, not just per roll. And keep in mind that cheaper doesn’t always mean worse, and expensive doesn’t always mean better. Upgrading to a higher-end underlayment with a stronger warranty often adds only a small cost to the overall project – but it pays off in long-term protection.
Looking for More Information on Underlayment for Metal Roofs?
Roofing underlayment is a complex topic. With all the different types and brands, it’s important to take your time and choose the option that makes the best sense for you. Feel free to visit the Metal Roofing Learning Center for more free info on underlayment and all things metal roofing.
And if you’re looking to install a metal roof, check out our Homeowner Hub, which provides content and resources specifically geared for homeowners. We can also help you get paired with a trusted contractor in your region through our Residential Referral Program. Reach out to us today!
