Design Specification No 1: Rooftop Disconnection

Downspout disconnect into grassy area

Design Specification No 1: Rooftop Disconnection

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This strategy involves managing runoff close to its source by intercepting, infiltrating, filtering, treating or reusing it as it moves from the impervious surface to the drainage system. Two kinds of disconnection are allowed:

  1. simple disconnection, whereby rooftops and/or on-lot residential impervious surfaces are directed to pervious areas
  2. disconnection leading to an alternative runoff reduction practice(s) adjacent to the roof
Downspout Disconnection
Downspouts should disconnect to an area that will allow the runoff to filter into the soil.

Alternative practices can use less space than simple disconnection and can enhance runoff reduction rates. Applicable practices include:

  • Soil compost amended filter path¬†[Stormwater (SW) Design Spec 4]
  • Infiltration by micro-infiltration practice (dry wells or french drains, SW Design Spec 8)
  • Filtration by rain gardens or micro-bioretention (SW Design Spec 9)
  • Storage and reuse with a cistern or other vessel (rainwater harvesting) (SW Design Spec 6)
  • Storage and release in a stormwater planter. (SW Design Spec 9, Appendix A)

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