If your gutters overflow regularly during heavy rains, you may want to consider adding an extra downspout. You can add a downspout to your gutters with little difficulty. Locate where you want to place your new downspout. Measure from the gutter to the wall of the house and then from the gutter to the ground. These two measurements will give you the approximate amount of straight downspout you will need. Purchase the downspout, a downspout connector and three elbows at any home improvement store.
Place a step ladder under the area you are installing the downspout. Measure in 4 inches from the end corner of the gutter with a tape measure, and mark the bottom of the gutter with a pencil.
Drill a hole in the bottom of the gutter at the 4-inch mark with a 1-inch hole saw attachment to the drill. Center the connector around the hole and trace the outside of the connector with the pencil.
Cut the tracing for the connector with a pair of sheet metal cutters. Clean the area around the hole with a shop rag inside the gutter and ensure that the area is dry. Place the connector in the hole with the lip of the connector on the inside of the gutter.
Secure the connector to the gutter using 3/8-inch sheet metal screws driven from under the gutter into the lip of the connector with a cordless screwdriver. Apply aluminum sealant around the inside of the gutter and the connector flange with a caulking gun.
Attach the first elbow to the connector and secure the elbow to the connector with one sheet metal screw. The elbow will slide around the connector under the gutter. Place the second elbow against the house 6 inches below the bottom of the first elbow. Measure the distance between the start of the curve on each elbow.
Cut a piece of straight downspout with a hacksaw according to your measurement. Assemble the straight piece into house elbow and secure with one sheet metal screw to the front and back side of the elbow. Slide the other end of the straight piece into the gutter elbow and secure with two sheet metal screws.
Measure from the wall elbow to the ground with a tape measure. Cut a straight piece of downspout to the measurement with a hacksaw, subtracting 8-inches from the measurement. Insert the downspout into the wall elbow and secure them together with two sheet metal screws.
Attach downspout straps to the house every 10 feet. Place the first strap 2 feet from ground level and secure the strap to the house behind the down spout with one screw. Bend the strap around the downspout and secure the strap to the downspout with a sheet metal screw. Cut off excess strap with a pair of sheet metal cutters.
Attach the last elbow to the bottom of the downspout with sheet metal screws. Place a splash block on the ground under the downspout to direct the rainwater away from the house.