What is stormwater management?
Stormwater runoff is rainwater that flows over roofs, driveways, and other impervious surfaces, potentially causing erosion, flooding, and pollution. Many cities require homeowners to manage stormwater by constructing a stormwater collection system, often called a “bio-retention basin.” These basins, designed by civil engineers, allow water to slowly seep into the soil. The basin’s size is based on the area of impervious surfaces created by the improvements.
Is stormwater management required for ADUs?
Stormwater management is not always required for ADUs due to their typically small footprint, often under 1,200 sqft. However, adding driveways, hardscape, and pools can push the total impervious area higher. Staying under 10,000 sqft is important because exceeding that makes your project a “Priority Development Project.” This designation brings more paperwork, fees, and higher construction costs.
What does stormwater management typically look like on ADUs?
As an ADU nears completion, gutters direct rainwater, and the site is graded to steer water toward a basin. Basins usually range from 30 to 75+ sqft, depending on the ADU’s size. Gutters must connect the roof to the basin, ensuring water flows correctly.
Maintaining the site and basin yearly is important. You must ensure runoff drains toward the basin and that the basin allows water to seep into the soil properly.
How much does stormwater management for ADUs cost?
Managing on-site stormwater through a bio-swale, drainage basin, or contouring costs around $5-10K. Basins are cost-effective within that range, depending on their size and design. With increasing building density, runoff and “cross-lot drainage” concerns grow. Poor drainage can lead to legal issues. Investing in a well-built basin now can prevent costly problems later. In short, an “ounce of prevention is worth a pound of cure.”
What are the storm water and erosion management requirements in Greater San Diego?
Several jurisdictions in Greater San Diego have stormwater management requirements for ADUs.
- Encinitas: ADUs over 500 sqft must include stormwater mitigation. Owners must record a covenant that prohibits removing the basin and allows city inspections.
- Vista: ADU regulations require site drainage and stormwater mitigation.
- Del Mar: ADUs must follow specific erosion control instructions, including the use of erosion control devices. A list of approved devices is available from the California Stormwater Quality Association.
Reach out to experts for your unique situation
At SnapADU, we provide valuable insights through our technical blogs. However, ADU regulations are constantly changing, and updates may occur after this blog’s publication.
We stay current with evolving regulations and industry trends. We work closely with clients on every project, ensuring we address any changes that may affect their requirements. This deep understanding of the regulatory landscape allows us to offer accurate guidance and customized solutions.
While our blogs contain helpful information, we encourage you to contact our team for personalized assistance. We’re here to help you navigate the complexities of ADU regulations, ensuring compliance and delivering optimal results.
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