How do gutter guards that slide under shingles work, and are they safe for your roof?
Short answer. Slide-under gutter guards have a back flange that tucks beneath the first course of shingles while the front rests on or clips to the gutter lip, so water runs from the roof onto the guard and into the gutter. They are inexpensive and quick to fit, but lifting shingles to install them can break seal strips and crack brittle shingles, so gutter-mounted guards are the safer choice.
How they are installed
- The installer lifts the first course of shingles at the eave.
- The guard's back flange slides under the shingles, ideally over the drip edge.
- The front edge rests on or clips to the gutter's front lip.
- The shingles are pressed back down, sometimes resealed with roofing cement.
The risks
- Seal strips: the factory adhesive bond under the first course breaks when lifted, so those shingles are more likely to lift and blow off in storms.
- Cracking: older or cold shingles crack when bent back.
- Wind uplift: a guard pushed under the shingles can act as a lever when wind gets beneath it.
- Warranty: shingle manufacturers may question coverage for damage at an edge that has been altered.
- Roof replacement: the guards have to come off when the roof is replaced, and gutters sometimes get damaged in the process.
If you already have them
Walk the yard and look along the eave for shingles that are lifted, wavy or missing near the guards, especially after windstorms. If the guards are working and the shingles are still sealed, you may leave them until the roof is replaced, then switch to a guard that mounts to the gutter and fascia. If shingles are lifting, have them resealed and consider changing the guards sooner.
Lower-risk alternatives
Some guards are designed to hook onto the drip edge rather than go under the shingles at all, which avoids the main risk. If a product's instructions call for lifting shingles, check the shingle maker's guidance first. See drip edge explained and gutter sizing, seamless gutters and guards.