Metal roofing underlayment which is best depends on your climate, budget, and roof type. The best underlayment protects your metal roof from water, ice, and heat damage. There are three main types: synthetic, felt, and rubberized asphalt. Each has different costs and lifespans. Metal roofs can last 40 to 80 years, so picking the right underlayment is key to making your roof last as long as possible. According to roofing industry data, metal roofing now holds about 17% of the residential roofing market share, making it an increasingly popular choice for homeowners.
What Is Synthetic Underlayment?
Synthetic underlayment is made from plastic polymers woven together. It does not break down like felt does. Synthetic underlayment breathes, which means water vapor can escape. This keeps moisture away from your metal roof.
Synthetic underlayment costs more upfront but lasts longer. It resists UV rays and tears better than felt. According to IBISWorld, the U.S. roofing contractor market reached $81.3 billion in 2025, with metal roofing systems being a growing segment. Many contractors now prefer synthetic because it stays in place during windy installations.
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What About Felt Underlayment?
Felt underlayment is the cheapest option. It is made from wood fibers and asphalt.
Felt breaks down faster than synthetic. It can rot if it gets wet for too long. It also shrinks and expands with temperature changes. This can create gaps under your metal panels. Felt works okay in dry climates but fails in wet areas.
Is Rubberized Asphalt Better?
Rubberized asphalt underlayment sits between felt and synthetic. It sticks to the roof deck and seals seams. This stops water from leaking through cracks.
Rubberized asphalt costs more than felt but less than synthetic. It tears more easily than synthetic. According to industry data, metal roofing can last 40 to 80 years depending on the material and installation quality. The right underlayment helps extend this lifespan. Rubberized asphalt works well in cold climates where ice dams form.
Underlayment Comparison Chart
| Underlayment Type | Cost | Lifespan | Best For |
|---|---|---|---|
| Synthetic | High | 20+ years | All climates |
| Felt | Low | 8 to 15 years | Dry areas |
| Rubberized Asphalt | Medium | 15 to 20 years | Cold climates |
For most metal roofs, synthetic underlayment is best. It lasts longer and protects better. According to ConsumerAffairs data, metal roofing is growing in popularity due to durability and weather resistance. If you live in a wet or icy climate, rubberized asphalt is a good second choice. Felt is fine only in dry areas where rain is rare. The cost difference is small compared to how long your roof will last.
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Contact a qualified roof contractor for expert guidance on roof repair, replacement, or installation.