No, gutter guards should not be installed under shingles, as this can interfere with the roofing system and may lead to problems with water flow or void the roof warranty. Instead, they should be attached to the gutter without affecting the shingles or roof structure.

Installing gutter guards under shingles can cause water damage and void roofing warranties. The best practice is to attach the guards directly to the gutter, allowing them to function properly without interfering with the roof's structure.