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The Role of Moisture Barriers in Metal Roof Installations

Investing time and attention in the correct installation of underlayment or moisture barriers is an essential step in ensuring the long-term performance, durability, and resilience of a roofing system.

Moisture barriers are installed before a metal roof. A moisture barrier, also known as roofing underlayment or felt paper, is a crucial component of the roofing system. Its primary function is to provide an additional layer of protection against water infiltration. Here is a general sequence of the roofing installation process, including the placement of a moisture barrier:


1. Decking Installation:

- The roof deck, which is the structural surface over which the roofing materials are applied, is installed first. It can be made of plywood or oriented strand board (OSB).


2. Moisture Barrier Installation:

- The moisture barrier is then installed over the roof deck. This underlayment serves as a waterproofing layer that helps protect the structure in case water penetrates the outer roofing materials.


3. Metal Roof Installation:

- Once the moisture barrier is in place, the metal roofing materials are installed. This can include various types of metal panels, such as standing seam panels, metal shingles, or metal tiles.


4. Flashing and Trim Installation:

- Flashing and trim components, which are essential for preventing water intrusion at vulnerable areas like roof edges, valleys, and penetrations, are installed along with the metal roofing.


5. Sealing and Fastening:

- Seams are sealed, and the metal roofing is securely fastened to the roof deck. Proper installation techniques are crucial to ensure a watertight and durable roofing system.


The moisture barrier acts as a secondary line of defense, providing protection in case water gets beneath the metal roofing materials. It is especially important in climates where heavy rain, snow, or wind-driven rain is common. The type of moisture barrier used can vary and may include asphalt-saturated felt, synthetic underlayment, or other specialized materials.

It's important to follow manufacturer guidelines and local building codes when installing a metal roof, including the specific requirements for moisture barriers. Additionally, proper roof ventilation is often considered to complement the moisture barrier and promote overall roof health.




Taking the time to properly lay underlayment or moisture barriers before installing a roof is crucial for several reasons:

1. Waterproofing:

- The primary function of underlayment or moisture barriers is to provide an additional layer of waterproofing. These materials act as a protective barrier against water infiltration, preventing moisture from reaching the underlying roof structure. Proper installation ensures a watertight seal, reducing the risk of leaks and water damage.


2. Structural Protection:

- Underlayment plays a vital role in protecting the structural integrity of the roof deck. It shields the deck from potential water damage, rot, and deterioration. By taking the time to lay the underlayment correctly, you enhance the longevity of the entire roofing system.


3. Preventing Mold and Rot:

- Moisture that penetrates the roof can lead to the growth of mold and the development of rot. These issues not only compromise the structural stability of the roof but also pose health risks. Properly installed underlayment acts as a barrier, minimizing the chances of moisture-related problems.


4. Enhanced Energy Efficiency:

- A well-installed moisture barrier contributes to the overall energy efficiency of the building. By preventing heat loss through moisture infiltration, the underlayment helps maintain a stable indoor temperature. This can result in energy savings and increased comfort for occupants.


5. Protecting Roofing Materials:

- Certain roofing materials, especially metal, may be susceptible to corrosion or damage if exposed to moisture. Underlayment serves as a protective layer, preserving the condition and performance of the roofing materials. This is particularly important for maximizing the lifespan of the roof.


6. Compliance with Building Codes:

- Many building codes and roofing material manufacturers require the installation of underlayment for warranty purposes. Taking the time to adhere to these guidelines ensures that your roofing system meets industry standards and provides the necessary protection.


7. Weather Resistance:

- Properly installed underlayment enhances the roof's resistance to various weather conditions, including rain, snow, and wind-driven rain. This is especially important in regions with unpredictable or severe weather patterns.


In summary, investing time and attention in the correct installation of underlayment or moisture barriers is an essential step in ensuring the long-term performance, durability, and resilience of a roofing system. It serves as a foundational element for a secure and reliable roof that can withstand the challenges posed by the elements.



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