Roofing Glossary

Fishmouthing

Fishmouthing is a distinctive shingle distortion where the center of a shingle tab lifts while the corners stay sealed — the tab gapes open like a fish's mouth. It is a close cousin of blistering and curling, and it shares their causes.

Fishmouths typically form when moisture trapped beneath or within the shingle expands, or when the shingle's adhesive seal releases unevenly and thermal movement distorts the tab. Poor ventilation and installation over damp conditions are the usual suspects.

An open fishmouth is a direct invitation to wind-driven rain: water enters the gap and sits against the underlayment or deck. A few isolated fishmouths can sometimes be hand-sealed; widespread fishmouthing indicates systemic shingle failure.

Why It Matters

Unlike surface-only blemishes, an open fishmouth is a functional breach — a gap in the water-shedding surface. They deserve prompt attention before wind-driven rain exploits them.

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