ADU rules in Sussex County, DE — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Sussex County adopted Ordinance No. 3027 on June 25, 2024, substantially rewriting its accessory dwelling unit (ADU) rules in Chapter 115 (Zoning) and Chapter 110 (Building Code). The new rules reclassify what had been called 'garage/studio apartments' since the late 1990s as ADUs, allow them by-right (no Board of Adjustment special use exception), permit attached or detached configurations up to 1,000 square feet, allow full self-contained kitchens for the first time, and apply only in unincorporated Sussex County - not inside the incorporated towns of Rehoboth Beach, Bethany Beach, Lewes, Dewey Beach, Fenwick Island, Henlopen Acres, South Bethany, Millsboro, Milford, Seaford, Georgetown, Milton, etc., which each have their own zoning codes. One ADU per lot is permitted, only on lots of at least 10,000 square feet, and on lots smaller than 3 acres a detached ADU must be located to the rear (behind) the principal single-family dwelling.
Sussex County's ADU framework is set out in Chapter 115 of the Sussex County Code (the County Zoning Ordinance) as amended by Ordinance No. 3027, approved by County Council on June 25, 2024. The ordinance amended Chapter 110 Article III and Chapter 115 Articles I, IV, V, VI, VII, VIII, IX and XXVII, replacing the older 'garage/studio apartment' terminology with 'accessory dwelling unit.' The County's ADU rules apply only in the unincorporated portions of Sussex County, including the heavily developed beach corridors outside the incorporated municipalities - so properties in unincorporated Long Neck, Angola, Oak Orchard, west of Rehoboth Beach, west of Lewes, north and west of Bethany Beach, and in the unincorporated portions of the Cape Region are governed by the County code, while parcels inside Rehoboth Beach, Bethany Beach, Lewes, Dewey Beach, Fenwick Island, South Bethany, Henlopen Acres, Millsboro, Georgetown, Milton, Selbyville, Frankford, Ocean View, Bridgeville, Greenwood, Blades, Laurel, Delmar, Seaford and Milford are governed by each town's own zoning code. ADUs are permitted in the AR-1 and AR-2 Agricultural Residential Districts (Chapter 115 Article IV), and by cross-reference in the GR General Residential District (Article VI), MR Medium-Density Residential, HR-1 and HR-2 High-Density Residential, and other residential zones referenced by Ordinance 3027. Key dimensional and use standards: (1) maximum floor area of 1,000 square feet; (2) the ADU cannot exceed 50% of the floor area of the principal single-family dwelling on the same lot; (3) the lot must be at least 10,000 square feet; (4) only one ADU is allowed per lot; (5) on lots less than three acres, a detached ADU must be located behind (to the rear of) the principal single-family dwelling; (6) ADUs may now contain self-contained kitchen space, making them fully independent living units (this was prohibited under the prior code); (7) ADUs may be attached, detached, or carved out of existing interior space such as a finished basement or above a garage; (8) standard front, side and rear setbacks of the underlying district apply, and detached ADUs must comply with the existing setbacks of the principal structure; (9) one off-street parking space is required for the ADU in addition to the parking required for the principal dwelling; (10) the lot must demonstrate adequate sewer capacity (Sussex County operates several centralized sanitary sewer districts; properties on private septic must meet DNREC On-Site Wastewater requirements before an ADU can be approved). Importantly, applicants no longer need to apply to the Sussex County Board of Adjustment for a special use exception - ADUs are now permitted by-right after staff review by the Sussex County Planning & Zoning Department. A building permit through the County is still required, and recorded private deed restrictions or homeowners' association covenants prohibiting accessory units take precedence over the County rules. Sussex County's broad zoning authority is granted by 9 Del. C. Chapter 68 (Sussex County Planning and Zoning) and Chapter 69 (Zoning); Delaware does not have a statewide ADU preemption law, so each jurisdiction sets its own rules.
Constructing or occupying an ADU in unincorporated Sussex County without a building permit, without satisfying the 1,000 sq ft and 10,000 sq ft lot thresholds, without providing the required off-street parking space, or in front of the principal dwelling on a lot of less than 3 acres violates Chapter 115 of the Sussex County Code and is enforced by the Sussex County Constable's Office and the Planning & Zoning Department. Common enforcement triggers include: converting a detached garage or shed into a rental unit without permits; building a second house on a lot below the 10,000 sq ft minimum; renting both the principal dwelling and an ADU as separate short-term beach rentals where deed restrictions prohibit it; exceeding the 1,000 sq ft cap; or installing a second kitchen without the required permits and inspections. Penalties under 9 Del. C. Sec. 6917 and Chapter 115 Article XXVIII can include daily civil fines, stop-work orders, and orders to remove or vacate the unit. Within incorporated towns the County rules don't apply - violations there are handled by the town's code enforcement officer under the town's own zoning code. Recorded HOA or deed-restriction violations are private matters enforced by the HOA in Delaware Court of Chancery, not by the County.
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