Metal roofing requires careful attention to detail. The layer beneath the metal panels, known as the underlayment, protects the roof deck and helps regulate indoor conditions.
We will explore three common types of underlayment for metal roofs—felt underlayment, synthetic sheet underlayment, and self-adhering membrane underlayment—to assist you in making the right choice for your roof.
What is Roof Underlayment?
Underlayment is a water-resistant material placed between the top roofing layer. It adds protection against weather impacts and moisture infiltration. Roof underlayment is usually positioned beneath other roofing materials and is commonly attached to the roof decking or sheathing. Three common types of underlayment are felt, synthetic, and self-adhering.
The Role of Underlayment in Metal Roofing
Underlayment acts as a barrier between the roof deck and the metal panels. Its main functions include:
- Moisture Shielding: Keeping snow and rain from reaching the roof deck.
- Thermal Protection: reducing temperature extremes on the roof deck.
- Noise Reduction: Reducing the sound of rain on metal surfaces.
- Ice Dam Prevention: Lowering the risk of ice build-up along the eaves in colder weather.
Does a Metal Roof Need an Underlayment?
This is a common question to ask. Most people know that a shingle roof needs to have an underlayment, but does that mean that a metal one does, too? There is a huge misconception that underlayment isn’t required for a metal roof; however, the opposite is true. While it may be accurate that a vapor barrier or something similar isn’t required for structural reasons, it does provide essential benefits for maintaining and preventing moisture from infiltrating your metal roof. It’s best to choose an underlayment that is designed to match the lifespan of your metal roof so you can protect the longevity of your roofing system.
Common Underlayment Options
What is the best choice for underlayment for your metal roof? A metal roof is a significant investment, so it is essential that you also invest in the best support that will provide optimal protection for your roof and property. Here are some options to keep in mind when considering the three most common underlayment choices:
What Is Felt Underlayment?
Felt underlayment is also known as felt paper, roofing tar paper, or asphalt-soaked felt. This traditional material is widely used for metal roofs, especially on steep-slope installations. It is available from many local suppliers and has been a common choice for years.
Advantages of Felt Underlayment
Cost: There is typically a low upfront cost, which is beneficial for projects with a limited budget.
- Water Resistant: The asphalt coating provides felt underlayment with an effective barrier against water, decreasing the likelihood of leaks during heavy rain.
- Familiarity: Many roof workers have experience working with felt, which can help speed up installation times.
- Availability: Its long history in the industry ensures that it can be found in most building supply stores.
Disadvantages of Felt Underlayment
- Heat Performance: In hot climates, asphalt can sometimes soften, lowering its ability to block water.
- Environmental Impact: The material is rarely recycled, which means that when it is replaced, it generates significant waste.
- Durability: Felt is more prone to tearing, especially when exposed to sharp edges or heavy foot traffic during installation.
- Lifespan: Felt tends to wear out sooner than other options, possibly requiring more frequent replacement.
What Is Synthetic Sheet Underlayment?
Synthetic sheet underlayment is made from polypropylene, polyethylene, and polymers. It is designed to protect the roof deck. This material has grown in popularity because it lasts longer and resists damage from UV rays, and it is high-heat better than felt.
Advantages of Synthetic Sheet Underlayment
- Lightweight: Its lower weight makes installation easier.
- Long Lifespan: The polymer blend helps this option last longer than felt.
- Flexibility: Synthetic sheets are suitable for various roof shapes, meaning they fit well on roofs with curves and angles.
- Water Barrier: This material has low permeability, which keeps water out, even in heavy rain.
- Heat Resistant: Unlike felt, this option maintains its form even in extremely hot weather.
Disadvantages of Synthetic Sheet Underlayment
- Handling: Extra care and attention are required during installation to avoid wrinkles or misalignment that might hinder its protective function.
- Ventilation issues: Its low permeability means that it can restrict airflow under the roof; this could lead to moisture issues if the roof isn’t properly ventilated.
- Cost: The initial price is higher compared to felt, which may affect some budgets.
What Is Self-Adhering Membrane Underlayment?
Self-adhering membrane underlayment is a peel-and-stick option that combines a rubberized, soft adhesive with a polyethylene carrier. It bonds directly to the roof deck and forms a continuous layer. This product is common in areas with severe weather, including ice formation, damp conditions, and high temperatures.
Advantages of Self-Adhering Membrane Underlayment
- Strong Bonding: The adhesive creates a tight seal with the roof deck, which reduces the chances of leaks.
- Ice Dam Prevention: Its properties help prevent water from seeping in during cycles of melting and refreezing.
- Smooth Appearance: Once applied, it forms a continuous layer that fits extremely closely with the roof deck.
- Air Barrier: The membrane can reduce drafts and help maintain stable, warmer indoor conditions.
- Temperature Resistant: Some versions withstand very high temperatures without losing adhesion.
Disadvantages of Self-Adhering Membrane Underlayment
- Installation Sensitivity: The material requires careful handling; improper application can result in bubbles or peeling.
- Higher Costs: This option typically comes with a higher price than felt aesthetic sheet underlayment, which may not be ideal for budget-conscious choices.
- Skill Requirements: Experienced professionals should install the membrane to ensure the adhesive bonds properly to the roof deck.
Cost and Durability Considerations
When choosing underlayment, budget plays a huge role because each option requires you to balance initial costs against the material’s lifespan.
Felt underlayment is available at a lower upfront cost and is easy to source and install; however, its shorter lifespan means it may need replacing more often, creating more waste when disposed of.
In contrast, synthetic sheet underlayment offers a longer lifespan and performs reliably across a range of different temperatures. Its higher purchase price and potential to restrict air circulation beneath the roof are factors to consider.
The self-adhering membrane underlayment bonds strongly to the roof deck, helping to prevent ice dams and performing well even under extreme temperatures. Although this option comes at the highest cost and requires careful professional installation, it may offer longer longevity.
Installation Considerations
The quality of your roof largely depends on the proper installation of the underlayment. It is best to have trained roofing professionals handle the application, as they will follow manufacturer instructions and established best practices. Before any installation, the roof deck needs to be thoroughly cleaned and dried because any remaining debris or moisture can weaken the bond between the deck and the underlayment. Ensuring that the underlayment sheets are laid with the proper overlap is important for preventing water from finding gaps. In some cases, specific installation conditions are needed. For example, self-adhering membranes must be applied within a certain temperature range for the adhesive to set properly.
Environmental Impact and Sustainability
The environmental impact of your underlayment choice is an important consideration. Felt underlayment, though appealing because of its lower cost, is rarely recycled and can produce significant amounts of waste over time. Synthetic sheet underlayment is made from polymers, which can carry a large production footprint. However, because it has an extended lifespan, it means that you may need fewer replacements and generate less overall waste. Sulfur during membrane underlayment involves a more complex production process; however, its longer service life and reduced need for repairs can help balance its environmental cost.
Making the Right Choice for Your Roof
Deciding on the right underlayment depends on factors such as your budget, local weather conditions, and the level of protection that your metal roof needs. In areas where you hardly experience extreme weather and cost is the main concern, felt underlayment might be the best option. For projects that require a long-lasting material with dependable performance across multiple temperatures, synthetic sheet underlayment could be a better match. If you live in an area that experiences ice formation or very high heat, sulfur during membrane underlayment provides a strong bond that helps keep damage and leaks at bay. Talking to us at RPS Metal Roofing, we can guide you through the best option for your roof, your needs, and your budget.