Redevelopment and infill offer opportunities to decrease the amount of impervious surfaces on an existing site. These lots can often be unused parking lots or abandoned buildings. Some of the sites may also pose health and environmental hazards if they are left in their current state, these are typically called brownfields. According to the Brownfield Redevelopment Strategy, there are potentially 8,195 sites throughout the region, although not all of these have been formally designated in brownfields. Brownfields in particular offer opportunities to reduce stormwater volume and improve quality by increasing the amount of green space on the site.
Teardowns provide unique challenges in stormwater management. A teardown is described as "one-to-one replacements of housing stock," by the Teardowns Strategy Report. Typically teardowns are much larger than the house they replace creating more impervious area on site. Since these lots are typically less than an acre, it is impractical to require land consuming stormwater management practices. The Teardown Strategy Report lists a number of recommendations for stormwater ordinances. These include maximum percent impervious on lots, strict setback requirements, maximum yard slopes, restrictions on topography alteration, site plan submittal requirements and maintenance of adequate overflow routes. These suggestions would increase the permeable area on site and reduce off site flooding.
DuPage County has updated its Stormwater Ordinance to encourage redevelopment in downtown areas by defining Stormwater Economic Development Zones (SERZ), which contain sites greater than one acre and which have existing impervious area over 80% of the site. The SERZ requires that the two-year detention requirements are met. This means that the post development release rate will be less than 0.04 cfs/acre half of the time. This ordinance tends to encourage redevelopment because a larger portion of a property can be built on rather than being set aside to meet the 100 year detention requirements. (Stormwater Management Division)