Synthetic Felt Underlayment
Synthetic felt is a lightweight, water-resistant roofing underlayment made from woven or spun polypropylene, serving as a secondary moisture barrier between the roof deck and the shingles.
The Modern Underlayment Standard
Synthetic felt underlayment is a polypropylene-based moisture barrier installed over the roof deck and beneath the shingles, replacing traditional asphalt-saturated felt paper as the industry standard on most residential roofing projects. Synthetic underlayment is lighter, stronger, and more water-resistant than traditional #15 or #30 felt. It lies flat without wrinkling, resists tearing during installation, and provides better foot traction for the crew.
On insurance estimates, the distinction between felt and synthetic underlayment matters because they carry different unit prices in Xactimate.
Why Synthetic Has Replaced Felt
Most major shingle manufacturers now recommend or require synthetic underlayment for full warranty coverage. This requirement is relevant to insurance claims because the replacement must meet manufacturer specifications. If the shingle manufacturer requires synthetic underlayment and the estimate includes only felt paper, the estimate is incorrect. This is a straightforward supplement with strong documentation: the manufacturer's installation instructions specify synthetic underlayment.
Synthetic underlayment also performs better in the field. It can be left exposed longer during installation without degrading, which matters on jobs where weather delays stretch the timeline.
Estimating Synthetic Underlayment
Xactimate has separate line items for synthetic underlayment and traditional felt paper. The synthetic product costs more per square. When writing or reviewing an estimate, verify that the correct underlayment type is specified. On a full roof replacement, the underlayment covers the entire deck area, so even a small per-square pricing difference adds up across the full roof. Reference the shingle manufacturer's installation requirements to justify synthetic underlayment if the carrier questions the material selection.
Frequently asked questions
Synthetic felt is lighter, stronger, more water-resistant, and easier to install than traditional felt paper. It lies flatter, does not wrinkle when wet, and provides better traction for installers. Most shingle manufacturers now recommend or require synthetic underlayment for full warranty coverage.
Yes. The estimate must specify the correct underlayment type. Synthetic underlayment costs more than felt paper, and using the wrong line item results in underpayment. If the manufacturer requires synthetic underlayment for warranty compliance, that requirement supports using the higher-priced line item.
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