How to Improve Downspout Drainage
One inch of rainfall drops 623 gallons of water onto the roof of a 1,000-square-foot home -- and through the gutter downspouts. The water can cause serious and expensive flooding and foundation problems if it collects around your house. To prevent this, help your downspout drain correctly. Here are several simple solutions, including straight and flexible extensions and various underground piping plans.
Add Downspout Extenders
If you have well-drained soil sloping away from the foundation, simple downspout extenders may be all you need to improve downspout drainage. There are 2 types: a straight, folding vinyl extension or an accordion-style flexible extender. These extenders can be twisted into any angle to suit your purpose -- for example, to move the downflow away from a patio.
Either extension should end on a splashblock. Some experts don't give much credence to plastic or cement splashblocks. They may not be the perfect solution for downspout drainage issues, but splashblocks at least spread water so it doesn't pool directly under a narrow downspout.
Pipe Water Away from House
To divert water farther from the house, consider a French drain or other trench drainage system. A French drain (named after American drainage expert Henry French, not the country) is a trench that slopes away from the house at least ¼-inch per foot and empties onto open ground far from the house. Fill the bottom of the trench with gravel, then lay in a flexible or solid pipe and cover with more gravel and soil or sod. The original French drains had no pipe, and you can make a hybrid system with a porous pipe.
Bury Drainage Pipes
If the yard doesn't slope enough for a French drain, you might need to build a more complex pipe trench. Most municipal ordinances no longer allow homeowners to attach downspout pipes directly to the storm sewer system. However, you can build an underground drainage system - a sloping, buried run of PVC pipe that pushes water into a gravel-filled posthole or a dry well, which is basically an underground plastic barrel with holes in the sides for water flow. Make sure to add a filter or overflow cap to simplify the removal of debris and allow excess water to escape during very heavy storms.
Finally, diverters can be used in conjunction with these other methods, but they are not a complete solution to drainage issues. Diverters draw water into a rain barrel from your downspout. Rain barrels can be used for irrigation and to spread water. Rainwater harvesting is a good way to collect water, but there are health warnings and legal concerns.
Rain barrels will probably not capture all the water flowing off the roof in a heavy rainstorm. A good diverter is designed to overflow back into the downspout and spill out onto the ground. You will still need extenders or piping to alleviate drainage problems.
Improving downspout drainage can be as simple as screwing on an extender or as complex as burying a barrel, but any method is cheaper and simpler than fixing potential foundation problems caused by rainwater pooling around your house. If you're not sure which system is right for your home, consult a professional roofer.
Updated February 18, 2018.