The traditional choice for roofing underlayment has been asphalt felt, but as technologies have developed, manufacturers are offering synthetic underlayments. Senior editor Martin Holladay takes a look at the various types of synthetic roofing underlayments and considers their pluses and minuses compared to felt. The biggest issue with many synthetics is permeance, which makes them effective vapor barriers. However, a strong vapor barrier is an asset only for certain roof styles. Care must be taken when attaching synthetic underlayments; cap fasteners are the best choice. Traction is also an issue as some synthetics can be slippery.
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