Roof Downspout Redirection Design Guidelines 

• What is a downspout?
• Planning Downspout Redirection
• Examples of Downspout Disconnects
• Installation
• Maintenance

What is a downspout?Water draining from a portion of a roof surface travels to the perimeter of the roof to a shallow trough called a gutter. The gutter moves water to a downspout, which is a pipe that carries rainwater from a roof to a drain or to the ground. See annotated photo below.



Downspout disconnection refers to the redirection of stormwater from an existing downspout to a vegetated landscape area or collection system. When it rains, the water travelling down the downspout would enter the landscape, rather than entering a storm drain below ground. When the water enters the landscape it slows down and is filtered and cleaned by movement through the soils and plant roots. Not only does this help keep the watershed clean, but adds an aesthetic landscape feature to a property. Planting design possibilities are endless. Planting with plants native to the Central Coast are encouraged.

When disconnecting a downspout, it is preferred that the water flows to your landscape in the form of a rain garden, vegetated swale, mulch basin; flows to a pervious surface such as a porous driveway; or is collected in the form of a rain barrel. It is not recommended to have the water flow onto a hardscape surface which flows to a storm drain in the street.

Additional benefits include:

•  Free “seasonal’ water for landscape
• Slows roof/downspout runoff; reducing peak stormwater flows
• Inexpensive and easy
• Add a rain chain or bowl for decoration
• Divert water flow into a rain garden or mulch basin

 

Planning Downspout RedirectionLocation Discharge

Determining the appropriate location and discharge surface or feature for your disconnected downspout is important to plan out. Please use the checklist to ensure that you comply with the design guidelines in terms of properly disconnecting a downspout.

• Decide which gutter you would like to disconnect
• Decide where and what feature you want to discharge water to flow to. Below are some ideas:
  • Rain Garden*
  • Vegetated Swale*
  • Mulch Basin*
  • Pervious Paving**
  • Rain Barrel(s)***
• Ensure that water slopes away from the discharge point
• Use splashblocks, river rock swales, gutter extensions, or other features to direct runoff and control erosion
• Downspout discharge water and runoff should not flow toward building foundations or onto adjacent neighboring private property
• Provide a cap to the stromwater inlet pipe if applicable

* Follow the RainScapes Creating Rain Gardens Design Guidelines
** Follow the RainScapes Impervious Surface Replacement with Pervious Surface Design Guidelines
*** Follow the RainScapes Rainwater Harvesting Design Guidelines 

Examples of Downspout Disconnects:  

 

InstallationDisconnecting a downspout is fairly easy, however you have the choice to hire a licensed landscape contractor to help. Below are general instructions on how to disconnect a downspout, however the process may change based on the method or /feature you intend to use with the discharge water.

Cut the downspout pipe with a hacksaw at an appropriate height. The height will vary depending on how you intend the discharge water; make sure you cut at a height that will fit to new downspout piping, elbow, extensions, rain chains, rain barrels, etc. you intend to use. Remove the remaining short section of downspout and securely cap the standpipe (pipe leading to underground stormdrain), if applicable.

Attach any new downspout piping, elbow, extensions, or rain chains you intend on using. Then place splashblocks, river rock swales, gutter extensions, or other features to direct runoff and control erosion.

See the graphic below of the process of disconnecting a downspout:



Graphic from Mid America Regional Council

Maintenance

• Clean your gutters at the beginning of each rainy season and as needed throughout the winter. 
• Check that the cap on the stormwater inlet pipe is secure.
• After major rain events, check that the gutter inlet is not clogged or blocked with debris.
• Check for leaks, damaged parts, rust.
• Evaluate any erosion potential from the discharge water.
• Follow recommended maintenance procedures applicable to the surface or feature the discharge water is flowing into (i.e. Rain Garden, Vegetated Swale, Mulch Basin, Pervious Surface, or Rain Barrel).