You want your gutters to work properly, and in order for them to do that, they need to have a slight downward angle to feed any running water toward the downspout.


Longer gutters (35 feet and longer) will slope from the center to each end. They will start at the same height in the middle and tilt downward to the edges, ending at the same point.
Shorter gutters should tilt from one end to the other. They should start at a high point and end at a lower point.
 If your fascia board is longer than 35 feet (10.6 m), your starting point will be in the center of the fascia board. If it's shorter than 35 feet (10.7 m), your gutter will run from one end to the other.


Mark the high point on the fascia, 1.25 inches (3.175 cm) below the roof flashing with a piece of chalk.
 This will be at the corner of a fascia board, and may include one downspout being fed by two different gutters.
 Starting at your high point, move down 1/2-inch for every 10 feet (3 m) of gutter.


For example, if you're working on a 25 foot (7.6 m) fascia board, your end point will be roughly 1-1/4 inch below your high point.
 Use a level or a measuring stick to try to get an even line. This will be a guidepost for your gutters, so it helps to be precise.
Measure and snap a layout line using a chalk line.
Locate the starting point, or highest point, of the gutter run.
Then, locate the ending point, or the downspout location, of the gutter run.
Find the end point of the gutter run by using a 1/2-inch (.635 cm) downward slope.
Snap a chalk line between the high and low points.
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