PRINCIPLE NO. 16 Direct Rooftop Runoff to Pervious Areas
Direct rooftop runoff to pervious areas such as yards, open channels, or vegetated areas and avoid routing rooftop runoff to the roadway and the stormwater conveyance system.
Notes:
Often, code requirements discourage the storage and treatment of rooftop runoff on individual lots, thus bypassing opportunities to promote bioretention and infiltration. Most subdivision codes require that yards have a minimum slope to facilitate drainage away from house foundations for fear of nuisance ponding, basement flooding, or ice formation on driveways or sidewalks.
Sending rooftop runoff over a pervious surface before it reaches an impervious one can decrease the annual runoff volume from residential development sites by as much as 50%. Some possible techniques to encourage treatment of rooftop runoff on-site include directing flow into stormwater treatment practices (infiltration swales, infiltration trenches, or dry wells), encouraging sheet flow through vegetated areas, directing runoff to depression storage areas, or using a rain barrel.