Felt paper, sometimes called tar paper, is a traditional roofing underlayment made of a base material saturated with asphalt, rolled out across the deck as the water-resistant layer beneath the shingles. It has been used for generations and is typically sold by weight per square, such as 15-pound or 30-pound felt, with the heavier weight offering more tear resistance and durability. Felt paper has largely been replaced by synthetic underlayment on new installations, though it still meets code in most areas and remains a valid, lower-cost option.
Long before synthetic underlayment existed, felt paper was simply what underlayment meant, and the material is still recognizable on plenty of roofs today: a dark, asphalt-saturated sheet rolled out in overlapping courses across the deck before the shingles go down.
Felt is graded by weight, historically expressed as pounds per roofing square, with 15-pound felt being the lighter, more traditional option and 30-pound felt offering a heavier, more tear-resistant sheet for the same coverage area. Heavier felt costs more per roll but tolerates rougher handling and foot traffic during installation.
What holds felt back compared with a synthetic alternative is mostly a matter of physical durability. Felt tears more easily underfoot, absorbs moisture rather than shedding it entirely, and can wrinkle, buckle, or start to break down if left exposed to sun and weather for more than a short stretch before the shingles cover it.
That exposure sensitivity matters on any job where weather might delay the shingle installation, since a felt underlayment left uncovered for days can already be showing wear by the time the crew is ready to shingle over it.
Felt still meets most current building codes as an acceptable underlayment, and it remains a legitimate, lower-cost choice on some jobs, particularly where cost is the deciding factor over the marginal durability gain synthetic offers.
The honest comparison on a set of quotes is not that felt is unsafe or non-compliant, but that it is the older of two valid options, and knowing which one a bid specifies is useful before assuming both quotes describe the same underlying protection.
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