09/02/2026
Most homeowners never see the most important layer of their roof—and this photo shows why.
This is GAF FeltBuster synthetic underlayment being installed before the shingles. For Oahu homes, it’s the waterproof barrier between shingles and the wood deck, protecting against wind-driven rain that can get underneath during storms. Unlike old organic felt that wrinkles, tears, and absorbs moisture, synthetic underlayment lays flat, resists tearing, and won’t rot if it gets wet before shingles go on.
Why it matters: when a roof leaks, the deck underneath often takes the damage. Rotten decking can turn a simple shingle job into a major repair, and it usually comes down to whether the layers below were installed correctly.
A pro roofing contractor ensures proper overlap, a smooth surface with no buckling, and clean seals around every penetration—details you’ll never see once shingles are installed.
If you’re planning a new roof or want to know how yours was built, FBC Roofing offers a free inspection and can walk you through every layer.