Synthetic Roofing Underlayments
These materials are tougher than felt, but do they perform as well?
Synopsis: The traditional choice for roofing underlayment is asphalt felt, but as technologies have developed, manufacturers are offering more 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.
A milestone in any construction project is drying in, usually defined as the day the roof sheathing is covered with underlayment. Building codes require the installation of asphalt felt for several reasons: Underlayment keeps the sheathing dry until the roofing is installed, it provides some protection against leaks in case wind-driven rain gets…