Roofing Glossary

Felt Underlayment

Felt underlayment — often called tar paper or roofing felt — is the traditional underlayment made from paper or fiberglass mat saturated with asphalt. It has been installed under shingles for the better part of a century, and it still does the job.

Felt comes in 15-pound and 30-pound weights, referring roughly to the weight per square. Thirty-pound felt is thicker and more durable, and it lies flatter for a smoother shingle installation. Fifteen-pound felt is lighter and cheaper but tears more easily and can wrinkle if it gets wet before shingles go on.

Felt's main weaknesses are its weight, its tendency to absorb water and wrinkle if exposed to rain mid-installation, and its lower tear strength compared to synthetics. Its main strength is cost and a century-long track record.

Why It Matters

Felt is perfectly serviceable, but most quality contractors today default to synthetic underlayment for its durability. If a quote specifies felt, ask whether synthetic is an option and what the price difference is.

Questions about your own roof? Request a free estimate or call Nucci Brothers Roofing at (301) 458-1003.