A downspout is a vertical pipe used to drain rainwater from a roof. For many years downspouts have been used to drain water away from buildings to protect foundations. They are usually directed onto a paved surface such as a driveway or into a standing pipe in the ground, either of which drains into a storm drain pipe.
Downspout disconnection is the process of detaching a downspout from the storm drain system so that the volume of water entering the storm drain pipes is reduced.
Why Disconnect Downspouts?
Decrease the Volume of Runoff
In Montgomery County, a 1-year storm event (the type of storm that is expected to occur every year) typically dumps 2.6 inches of rain. If your roof is 1,000 square feet (average for the area), about 1,560 gallons of water will run off the roof, into your downspouts, and into the storm drain system over the course of the storm. Downspout disconnection keeps more of that rainfall on-site and reduces the amount of water that flows directly into the sewers. This helps reduce the amount of erosion caused by high volumes of water that flow from storm drain outfall pipes into local waterbodies.
Improve Water Quality
Rainwater that flows down your downspout and does not enter a sewer directly runs over driveways, sidewalks, roads, and lawns before it enters
the sewer system. Water that moves over the surface as runoff picks
up and transports pesticides, fertilizer, oil, litter, and other
pollutants on its way to the storm drain. This pollutant-laden rainwater
pollutes waterways, lowers water quality, and harms fish, wildlife,
and plants in local streams. Disconnecting downspouts and collecting
the water or allowing it to soak into the ground (infiltrate) has two benefits; It reduces
the amount of polluted runoff (also called nonpoint source pollution),
and it directly improves the water quality of local streams.
You can benefit from disconnected downspouts, too! A disconnected downspout might reduce your demand for County water if you capture and reuse the water. This will have a direct effect on your monthly water bill.
You can use collected water to:
- Water houseplants or a garden
- Rinse off gardening tools or outdoor furniture
- Wash cars and windows
- Keep your compost bin moist
This downspout disconnection drains to a driveway with pervious pavement. Pervious pavement allows the rainwater to soak into the ground instead of running off.
This downspout disconnection drains to a grassy area that absorbs the runoff into the ground.
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How to Disconnect Your Downspout
The procedure for disconnecting your downspout will vary depending on where you are directing the downspout water. The simplest form of downspout disconnection is to redirect the water from a downspout that currently drains to an impervious (hard) surface to a grassy area, a conservation landscape (a landscape designed to reduce human impact and improve the local environment), tree roots, or a rain garden.
General Instructions for Redirecting Downspouts onto Landscaping Away from the House
- Cordless drill
- Tape measure
- Sheet metal screws
- Downspout elbow
- Downspout extension
- Standpipe cap
- Using a hacksaw, cut the existing downspout approximately 9 inches above the sewer standpipe.
- Cap the sewer standpipe.
- To attach the elbow, first crimp the downspout with pliers to ensure a good fit. Connect the elbow to the downspout using sheet metal screws. It might be necessary to pre-drill the holes.
- Attach the elbow to the extension and secure it with sheet metal screws. The rainwater should drain at least five feet away from the house, so direct the extension accordingly. A splash block might help direct water farther from the house.
General Instructions for Redirecting Downspouts into Rain Barrels/Cisterns
You can connect your downspout disconnection to a rain barrel or cistern. When there is overflow from the rain barrel/cistern, it can be directed overland or back into a downspout if there is nowhere else to store it. Follow the instructions from the manufacturer of your rain barrel or cistern, or consult the Department of Environmental Protection's RainScapes program. The program offers resources for rain barrel construction, installation, and siting.
Cut some of the length from the downspout. Place the barrel nearby to get a rough idea where to cut.
Level out the ground beneath the downspout. Position heavy concrete blocks in place to support the rain barrel.
Place the barrel on top of the blocks.
Place one end of the downspout extension over the downspout.
Cut a hole in the lid of the barrel, and fit the other end of the fitted downspout piece into the barrel.
Your rain barrel is now installed.
Pictures and captions courtesy of Playing in the Dirt blog
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When you disconnect your downspout, consider the following:
- Disconnections must be designed to direct water away from foundations to prevent basement seepage.
- Disconnections are not recommended for residential lot sizes smaller than 6,000 square feet or where soil compaction prevents water from infiltrating.
- When channeling your disconnected downspout, make sure the entire vegetated area is on a slope of 5 percent or less.
- The area of rooftop contributing to each disconnected downspout should be no greater than 500 square feet.
- Where provided, downspout disconnections must empty at least 6 feet away from the nearest driveway or sidewalk to discourage "re-connections" into nearby storm drains or curb inlets.
- Where a gutter/downspout system is not used, the rooftop runoff must drain as sheet flow from the structure or drain to a dry well.
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