What is underlayment?

Underlayment is a protective layer positioned between your roof deck and shingles. When rain or snow enters gaps in shingles or works its way under them, underlayment catches that water and directs it safely toward the gutters and eaves, keeping moisture from reaching the wood and insulation below.

Two main types are common in Greater Hartford installations. Felt underlayment, traditionally made from wood fibers and asphalt, has been a standard for decades and remains code-compliant in most situations. Synthetic underlayment, a newer alternative made from woven plastics or polypropylene, offers longer durability, better traction during installation, and improved resistance to tearing and rot. Synthetic types typically last longer and perform better in high-moisture conditions, though felt remains widely used and still provides solid protection when properly installed.

Building codes across Connecticut require some form of underlayment on most roof slopes. Its role becomes critical in valleys and along eaves, where water concentration is highest. Poor or missing underlayment can lead to interior damage that takes years to reveal itself, making it a permanent part of the building envelope rather than a maintenance-only feature.

When hiring for roof replacement or installation, confirm what type your contractor recommends and why. Local contractors in the Hartford area typically choose based on roof pitch, climate exposure, and your home's specific vulnerabilities.