CONTACT INFORMATION Rooftop Detention - …

1 CONTACT INFORMATION . You can CONTACT the following city agen- Rooftop Detention cies by calling 311, the city 's non-emergen- cy government INFORMATION and services hotline, or by calling the agency numbers A Low-Cost Alternative for listed below: Complying with New york NYC Department of Environmental Protection (DEP) city 's Stormwater Detention 718-595-5223. Requirements and Reducing NYC Department of Buildings (DOB) Urban Runoff 718-566-5280. NYC School Construction Authority (SCA). 718-472-8332. WHAT IS Rooftop Detention ? Rooftop Detention , also known as a Blue Roof or controlled-flow system, is an easily installed, cost-effective alternative to temporarily store and gradually drain rainwater off a build- ing's Rooftop . Detaining rainwater helps to slow its rate of release into the sewer system for a maximum period of 24.

2 Hours. It also helps to reduce runoff during peak rainstorms so that more combined sewer flows can be treated at wastewater treatment plants and risks of street and driveway flooding and sewer back-ups in basements are lowered. Rooftop Detention can play a role in ensuring that our sewer systems are not overwhelmed during rainstorms 59-17 Junction Boulevard and our waterways are protected from Flushing, NY 11373. pollutants in urban runoff. Printed on recycled paper 3/12. HOW Rooftop Detention WORKS Is easy to install and maintain, similar to a Water Depth: Water depth on the Rooftop Controlled-flow roof drains regulate the standard roof. should not exceed two-to-four inches and flow of Rooftop drainage. Small weirs Extends the life of the roof through a should not be stored for longer than 24. (openings), as shown in the drawing secondary membrane, or other waterproof- hours.

3 Depths much shallower than three below, are placed inside the inlets of roof ing roofing system. inches are typically required to satisfy Detention requirements. drains to capture rainwater and slowly Is an approved practice under New york release it. Stormwater builds up to a Scuppers and Overflow Drains: Roof should city 's construction and sewer connection predetermined depth and drains at a be designed with multiple outlets and codes. unrestricted overflows. Scuppers (wall desired maximum rate. Rooftop Detention Costs considerably less than other ap- outlets) should be placed in the parapet. requires that a secondary waterproofing proved Detention measures, such as membrane, or other waterproofing roof- Number of Drains: A minimum of two subsurface Detention . Costs are estimated ing system, be applied.

4 Drains in roof areas of 10,000 sq. ft. or less;. at an additional $5/sq. ft. over a standard and a minimum of four drains in roof areas roof. larger than 10,000 sq. ft. Provides similar stormwater benefits as Load Bearing Capacity: Although rooftops Multi-Weir Barrier green roofs (although green roofs provide Flashing Clamp are generally built to accommodate rainfall and Gravel Stop additional environmental benefits) at a build-up and snowpack, Rooftop Detention fraction of the cost approximately may require additional structural supports. $5/sq. ft. for blue roofs vs. $30/sq. ft. for This will depend on the depth of water green roofs. detained, HVAC and other Rooftop equip- ment, as well as further considerations. DESIGN CONSIDERATIONS. The following are some design consider- Deck Plate CASE STUDIES.

5 Trapezoidal Weir ations for installing a Rooftop Detention Opening Limiting The New york city School Construction system. The architect and/or engineer on Flow Rate to Leader Authority (SCA) is a pioneer of Blue Roofs the project will make site-specific determi- citywide. Over the last three years, SCA. HOW CAN Rooftop Detention nations of structural or other design needs has installed Rooftop Detention in 14 new BENEFIT YOU? for the project. schools. For SCA, the decision was initially In addition to providing benefits for the Application on Flat Roofs of New Structures. an economic one. The costs of Rooftop city 's waterways and sewer systems, Following good design practices and the Detention were far lower than for subsur- Rooftop Detention offers many advantag- requirements of the New york city con- face Detention .

6 The systems installed have es to the developer, building owner, and struction codes will ensure optimal perfor- required essentially no maintenance and tenants. A Blue Roof: mance and low maintenance of a Rooftop Detention system. there have been no problems with leak- Requires no additional land area, so it is age. We have been extremely pleased with well-suited to high density urban areas Waterproofing: Rooftop Detention requires the performance of our Rooftop Detention where land is limited. the installation of a secondary waterproof- systems. The engineer should consider this ing membrane, or other waterproofing innovative roof drainage design strategy.. roofing system. Harry Cethoute, , SCA.