Guidelines for designing and building Accessory Dwelling Units

Building an Accessory Dwelling Unit (ADU) requires careful consideration of local regulations, property constraints, and utility requirements. While ADUs offer a way to add living space for family or rental income, successful construction depends on several critical factors.

In Rhode Island, state law enables owner-occupied residential lots to add one unit within an existing structure by right. However, detached units remain subject to varying local dimensional and utility rules across different municipalities. Common constraints include size caps, setbacks, and sewer or septic capacity.

Key considerations for any ADU project include:

• Space and Setbacks: Local building rules dictate where a structure can sit, its maximum height, and its proximity to property lines. For instance, San Diego has specific requirements for detached ADUs based on fire safety and coastal location.

• Utility Connections: Access to electricity, water, sewer, and heating/cooling is essential. The distance between the ADU and existing connections can significantly impact construction budgets due to the cost of trenching and potential necessary utility upgrades.

• Construction Standards: The type of unit, such as a park model built to recreational vehicle standards versus a code-built cottage, will determine different permit paths and costs.