When installing drip edges and gutters, ensure that the lower edge of the roof hangs less than 1 inch beyond the fascia board and that the roof's edge has no flashing or overextended shingles. Additionally, ensure the gutters don't hang too high or low to be useful.
When the lower overhang of a roof doesn't extend outwards enough beyond a drip edge, water can drip behind the gutters. This rots the roof sheathing and fascia, stains siding, and causes more serious problems if left unchecked, such as soil erosion and basement flooding. Similarly, roof shingles extending off the roof deck or ice barrier should extend over a metal drip edge without extending too far outwards.
Don't attempt to compensate for the lack of a drip edge by installing shingles further forward than necessary. Avoid making this mistake when installing a drip edge or gutter system by measuring an optimal distance between the shingles and gutter system. This tip is as valid for the vertical distance between the roof and gutter as it is for the horizontal distance. Installing the gutter directly beneath the roof isn't always ideal, especially in cold climates where melting snow can pull the entire system away from the home.