To ensure that the gutters drain properly, make sure they are tilted (½ inch per 10 feet) toward a downspout. For gutters larger than 40 feet, it is best to tilt the gutter down from the center to a downspout at each end. Or, you can tilt the gutters downward from each end to a single downspout placed in the center of the duct. Determine what works best for your home before ordering gutters and accessories.
If you are replacing a gutter, once you have removed the old gutter, prepare the fascia plate with primer. If the fascia is damaged or rotten, replace it. Then determine the correct slope of the gutter and draw a chalk line on the fascia to use as a reference. The gutters should be tilted 1 inch every 20 feet toward the downspout.
Gutters over 35 feet long must have a downspout at each end, tilting the gutter from the center to each downspout.