Underlayment for Metal Roof and the Material Types

Underlayment is a crucial layer placed underneath the metal roof system as the waterproofing method and thermal protection for a building. It is vital, as the metal roof can become extremely hot on summer days due to high temperatures, cold during winter, and noisy during rainy weather.

However, choosing underlayment for a metal roof is a matter. This article will guide you through selecting the best and most suitable material for your metal roof.

Best Underlayment for Metal Roof

You might have wondered, what do you put under a metal roof? The answer is underlayment, which consists of water-resistant or vapor barrier material. This piece is installed directly on the roof system’s decking to combat extreme weather and climate conditions.

Underlayment for Metal Roof

If you aren’t using underlayment for a metal roof, the roofing system and the rest of the building might be exposed to elements such as moisture, wind, resin, or chemicals.

Read also: Metal Roof Underlayment

Selecting the best underlayment is important to maintain the lifespan of your home. Three underlayment types are most commonly available, which you can read about below:

Felt underlayment

This underlayment might be referred to by different names, such as asphalt-saturated felt, roofing tar paper, or felt paper. Compared to the other types, it is the most used because it is readily available almost everywhere and is more affordable. It typically measures around 30 mils thick, providing adequate protection.

Synthetic Sheet Underlayment

The second underlayment material, synthetic sheet, is a water-resistant protective barrier made by spinning or weaving polypropylene or polyethylene with a polymer. It offers better durability than felt and is becoming increasingly popular.

Self-adhering membrane underlayment

The last underlayment material is the self-adhering membrane, a type of rubberized asphalt peel-and-stick item adhered to the roof deck. It’s considered the most suitable for high-temperature underlayment because it can resist temperatures up to 240ºF.

This material includes butyl-based adhesive for superior adhesion, an effective air barrier material.

Using underlayment can also provide ice dam protection for areas prone to freezing temperatures, ensuring that ice does not damage the underlying structures of the standing seam metal roof.

Synthetic Metal Roof Underlayment

As mentioned previously, synthetic underlayment is a newly innovated material currently taking over the industry. This protective sheet layer is considered a good underlayment to use on metal roofs because of its qualities. Here are the advantages and disadvantages of using this material:

Synthetic Underlayment for Metal Roof


Many homeowners choose to use synthetic sheets because:

  • It generally has better durability compared to the felt underlayment
  • It has a higher resistance to various types of damage, moving, or tearing because it is created with thermoplastic polymers.
  • It has quite a good tolerance for extreme temperatures.


The downsides of using synthetic sheet underlayment for a metal roof are:

  • It is pricier compared to the felt underlayment
  • It has a low rating or permeability, so it is not the best material to have proper ventilation, but otherwise, it is great to combat moisture.

Is Underlayment Necessary for Metal Roof

Metal is definitely a durable material for roofing systems. In fact, they can last up to 70 years. Its resistance to weather, such as blizzards or rainstorms, and its excellent durability are part of why it is commonly used worldwide.

However, it still needs to be taken care of to last as long as it should. If you are still wondering if adding underlayment for a metal roof is necessary, then the answer is yes! Underlayment is highly recommended to be added to metal roofing.

There are many potential issues if you choose to go without it, such as roof leakage, trapped moisture, and other problem assortment that might deteriorate the quality of your roofing system and reduce the metal roofing’s longevity in the years to come.

Gravatar Image
RoofLast is an experienced author and roofing expert. With years of practical experience in the field authored several informative articles on various aspects of roofing, including installation, maintenance, and repair