Materials & Shingles · FAQ

Why did Trill stop installing 15-pound felt underlayment?

Three reasons, all observed on Illinois jobs. First, felt tears under foot traffic during install, leaving gaps that turn into leaks within the first storm. Second, felt absorbs water if a tear-off gets interrupted by rain, and saturated felt loses 70% of its tear strength. Third, the asphalt impregnation in felt off-gases on hot summer attic days, accelerating degradation of the decking and the underside of the shingles.

Synthetic underlayment solves all three. It tears like polyester rather than paper, sheds water, doesn’t off-gas, and weighs about a quarter of what felt weighs. The cost difference is roughly $20 per square (synthetic is more expensive), which on a typical job adds $600 to $700. Trill includes synthetic on every installation.