Adding an Accessory Dwelling Unit (ADU) to your property in San Diego can increase its value by up to 30%, with some cases seeing boosts of 50% or more. The exact increase depends on the ADU type (detached, attached, or interior), its size, quality, and the local housing market. Detached ADUs typically offer the highest value increase due to their independence, while conversions like garages may offer a higher return on investment due to lower construction costs. Local housing demand also significantly influences the added value of an ADU.