Proper downspout installation is important so water coming off the roof into the gutter can be diverted to control erosion and prevent water from accumulating near an exterior wall of the house. There are several common mistakes that installers can make that will affect the proper operation of downspouts and possibly cause damage. Make sure the downspout is the right size for the gutter.
Not adequately soldering the outlet tube to the base of the gutter will cause leakage. The tube should have a 3/8 inch soldered flange bend back. The downspout should be screwed or riveted to the tube. Not soldering the elbows is another frequent mistake. Not using enough downspout brackets can cause the pipe to pull away from the house or blow off in strong winds. Brackets should be placed every 10 feet.
A common error is only using one downspout for large roof areas, causing water to overflow the gutter. For runs over 40 feet there should be 2 downspouts with the high point being the middle of the gutter and a downspout at each end. Not extending downspouts far enough from the wall will cause water damage. Splash blocks should always be used at the end of the downspout to aid in water run off.