what to put under metal roof

3 min read 25-12-2024

Metal roofs are incredibly durable and long-lasting, offering excellent protection for your home. But to maximize their performance and lifespan, choosing the right underlayment is crucial. This guide will walk you through everything you need to know about what to put under a metal roof. We'll cover different underlayment options, their pros and cons, and help you make the best choice for your specific needs.

Understanding the Purpose of Underlayment

Before diving into specific products, let's clarify why underlayment is essential. It's not just an extra layer; it serves several vital functions:

Water Protection: This is the primary role. Underlayment acts as a secondary barrier against water penetration, especially in case of leaks in the metal roofing itself.
Wind Protection: It helps prevent wind-driven rain from getting underneath the roofing system.
UV Protection: Underlayment shields the roof deck from harmful ultraviolet (UV) rays, which can degrade wood over time.
Added Insulation (In some cases): Certain underlayments offer additional insulation properties, improving your home's energy efficiency.

Types of Underlayment for Metal Roofs

Several types of underlayment materials are suitable for metal roofs, each with its own advantages and disadvantages:

1. Felt Underlayment (Organic Felt)

Pros: Inexpensive, readily available.
Cons: Susceptible to moisture damage, less durable than synthetic options, offers minimal UV protection. Not ideal for long-term protection.

2. Synthetic Underlayment

This is generally the preferred choice for metal roofs, offering superior performance and longevity compared to felt. There are several types within this category:

Pros: More durable, water-resistant, better UV protection, often includes features like improved tear resistance and breathability.
Cons: More expensive than felt.

Types of Synthetic Underlayment:

Polyethylene (PE) Film: A basic, cost-effective synthetic option. Less durable than other synthetics.
Polypropylene (PP) Film: Stronger and more resistant to tears than PE film.
Rubberized Asphalt: Offers good water protection, but may not be as breathable as other synthetics.

3. Advanced Synthetic Underlayments

These high-performance underlayments offer enhanced protection and features:

Self-Adhering Underlayment: Features a sticky backing for easy installation and secure adhesion to the roof deck. Provides a reliable seal and reduces the chance of slippage.
Breathable Underlayments: Allows moisture vapor to escape from the building, preventing trapped moisture that could lead to mold growth.

Choosing the Right Underlayment: Key Considerations

The best underlayment for your metal roof will depend on several factors:

Climate: In areas with heavy rainfall or snowfall, a more durable and water-resistant underlayment is essential.
Budget: Felt is the most economical choice, while advanced synthetic options are more expensive.
Roof Pitch: Steeper roofs may require underlayment with greater wind resistance.
Building Codes: Check local building codes for specific requirements regarding underlayment.

Installation Tips for Metal Roof Underlayment

Proper installation is crucial to ensure the underlayment's effectiveness. Here are some general guidelines:

Clean the roof deck: Remove all debris and loose materials before installing the underlayment.
Start at the lowest point of the roof: Overlap the underlayment sheets according to the manufacturer's instructions. Typically, this is 6 inches minimum.
Secure the underlayment: Use roofing nails or staples to fasten it securely to the roof deck.
Ensure proper ventilation: Adequate ventilation is vital to prevent moisture buildup.

Frequently Asked Questions (FAQs)

Q: Can I use felt underlayment under a metal roof?

A: While possible, it's not the ideal choice. Synthetic underlayments offer superior protection and longevity.

Q: Is self-adhering underlayment worth the extra cost?

A: Yes, for many homeowners. The ease of installation and added security against leaks often justify the higher price.

Q: How long does metal roof underlayment last?

A: This depends on the type of underlayment. Synthetic options typically last much longer than felt, sometimes for decades.

Conclusion: Protecting Your Investment

Investing in a high-quality metal roof is a significant undertaking. Protecting that investment with the right underlayment is essential. By carefully considering the factors discussed in this guide, you can choose the best underlayment to ensure your metal roof provides decades of reliable performance and protection for your home. Remember to always consult with a qualified roofing professional for specific advice tailored to your project.