Fish mouth is a common shingle problem that usually shows up near the ridge after the roof is finished. It makes shingles lift, curl, or refuse to lay flat, turning an otherwise clean install into a visible quality issue.

On steep roofs, fish mouth is almost always caused by how shingles are handled and staged before they are installed.

Fish mouth is caused by bending shingles over the roof ridge to stop them from sliding.

It leads to lifted shingles, poor sealing, reduced wind resistance, and failed inspections.

BMF Shingle Anchors prevent fish mouth by holding shingles flat on the roof deck, eliminating the need to bend them over the ridge.

Fish mouth is a deformation in asphalt shingles that occurs when shingles are bent backward over the roof ridge and left under their own weight or the weight of a bundle.

That bend creates a permanent crease or curl. Once installed, the shingle will not lay flat and the edge lifts, resembling an open fish mouth.

This is not a manufacturing defect. It is a handling issue.

Steep roofs create one main problem. Shingles want to slide.

To deal with that, installers often rest bundles or loose shingles over the ridge because it feels like the easiest way to keep them in place.

On steep pitches, this leads to:

• Shingles being bent over a sharp edge

• Heat softening the asphalt

• Weight locking the bend into the shingle

Even a short amount of time can permanently deform shingles, especially in warm weather.

Fish mouth is not just cosmetic.

• Shingles may not seal properly

• Wind resistance is reduced

• Nail lines can lift or telegraph through

• Roofs may fail inspection

• Manufacturers can deny warranty claims due to mishandling

Homeowners notice it immediately, and inspectors do too.

Fish mouth almost always comes from convenience on the roof.

Common causes include:

• Resting bundles on the ridge

• Draping loose shingles over the peak

• Using the ridge as a staging area

• Leaving shingles bent during hot weather

• Trying to stop sliding by folding the shingle

The core issue is using the ridge to solve a sliding problem.

Fish mouth happens when shingles are bent to stop them from sliding.

BMF Shingle Anchors eliminate the need to bend shingles at all.

Instead of resting material on the ridge, shingle anchors allow installers to stage shingles and bundles flat on the roof deck, even on steep slopes. The anchor physically holds the material in place.

This helps by:

• Keeping shingles flat in their factory shape

• Distributing weight across the deck instead of over the ridge

• Preventing permanent creases and curls

• Allowing safer, cleaner material staging on steep roofs

Shingle anchors solve the sliding problem without damaging the shingle.

• Do not rest shingles or bundles on the ridge, unless using Shingle Anchors

• Even short exposure can permanently deform shingles, especially in warm weather.

• Always stage shingles flat on the roof deck

• Shingles are designed to stay flat. Any backward bend increases the risk of curling.

• Avoid using the ridge as a stopping point

• The ridge should be a transition area, not a staging area.

• Watch heat and timing

• Hot days soften asphalt quickly. The longer shingles sit bent, the worse the damage becomes.

• Secure materials instead of bending them

• If shingles want to slide, control them with proper anchoring instead of folding them over the peak.

• Use shingle anchors on steep slopes

• BMF Shingle Anchors hold shingles in place flat on the deck, eliminating the need to bend them to stop movement.

If you want shingles to lay flat, seal properly, and pass inspection, they need to stay flat from the moment they hit the roof.

Avoid using the ridge as a staging area. Keep shingles on the deck. Secure them properly.

That is how you prevent fish mouth before it ever starts.