Sussex County

Permits for ADUs on parcels in unincorporated Sussex County are issued by the Sussex County Planning & Zoning Office (zoning compliance) and the Sussex County Building Code Department (building permit). Under Ordinance 3027 (2024), ADUs are a by-right use in the Agricultural Residential (AR-1, AR-2), Medium-Density Residential (MR), General Residential (GR), High-Density Residential (HR-1, HR-2), and Urban Residential (UR) districts provided the parcel meets the 10,000 sq ft minimum, 50% lot-coverage cap, and the ADU does not sit in front of the primary residence on parcels under 3 acres. No Board of Adjustment special-use exception is required for an ADU that conforms to Article XXV; a non-conforming proposal still needs a variance. Incorporated municipalities inside Sussex (Rehoboth Beach, Lewes, Bethany Beach, Milton, Seaford, Milford, Georgetown, Laurel, Bridgeville, Millsboro, Selbyville, Dagsboro, Delmar, Frankford, Greenwood, Ellendale, Bethel) handle their own ADU permits through their own code-enforcement offices and are NOT covered by this unincorporated-permitting record.

Process overview: Under Ordinance 3027, an unincorporated-Sussex ADU is typically permitted as a combined zoning/building intake: (1) applicant confirms the parcel is 10,000 sq ft or larger and in a residential district where ADUs are permitted, (2) submits a site plan showing setbacks, lot coverage, and ADU placement relative to the primary residence, (3) Planning & Zoning staff reviews for Article XXV conformance (size ≤ 1,000 sq ft, one off-street parking space, required setbacks), (4) Building Code reviews construction drawings for IRC compliance, (5) if the parcel is within a mapped flood zone or tax ditch right-of-way, DNREC/floodplain review is layered in, (6) construction inspections, (7) certificate of occupancy. Proposals that fail any Article XXV test (e.g., exceeding 1,000 sq ft, placement in front of primary residence on a sub-3-acre lot) must seek a variance from the Board of Adjustment before proceeding.

Impact fees: Sussex County does not levy general residential impact fees in the manner of many western counties; residential development fees are concentrated in the building-permit fee schedule and parcel-specific sewer-capacity fees. ADUs on parcels served by Sussex County Engineering sewer districts require adequate sewer capacity and may incur a system-development charge (SDC); parcels on private septic require DNREC Division of Water septic-system sizing review for the added fixture count. (schedule)

The Sussex County Assessment Office maintains parcel-level assessment records for all real property in Sussex County, including parcels within incorporated municipalities. ADU additions are assessed as improvements to the host parcel; Delaware does not permit separate tax-parcel creation for an accessory dwelling unit that shares a lot with the primary residence. Sussex County completed its first county-wide reassessment since 1974 in spring 2025 (court-ordered; see Vaughn v. Carney, Del. Ch. 2020-0047-JTL, and the statewide reassessment consent order). Tentative values were mailed November 2024; the Board of Assessment Review heard appeals beginning March 2025; new tax bills reflecting the reassessment arrived in early August 2025 for the 2025-2026 tax year. The county tax rate was lowered to offset the higher assessed values, but school districts retain authority to increase their rates up to 10% without a referendum, so total bills moved unevenly across the county. Going forward, ADU additions are captured on the next physical-inspection cycle or via self-reported improvement on the building permit.

Assessment policy: No Delaware-state ADU-specific exemption exists. Sussex County captures ADU improvements through the building-permit pipeline (permit-triggered inspection) and through the periodic reassessment cycle (the first post-1974 revaluation completed 2025; no fixed future cycle is codified, though the consent order contemplates regular revaluation going forward). Parcels with ADUs are assessed on the total improved value; there is no separate ADU-only line or rate. Sussex County's effective property-tax rate sits near 0.33% of assessed fair-market value after the 2025 reassessment — the lowest in Delaware and among the lowest effective rates on the East Coast — but that rate is exclusive of the school-district levy, which is the dominant component of most Sussex tax bills.

Sussex County administers a Flood-Prone Districts overlay (Chapter 115 Article XVIII) that implements FEMA NFIP standards countywide; roughly 20% of Sussex parcels sit within a mapped Special Flood Hazard Area (SFHA), heavily concentrated along the Atlantic coast (Rehoboth, Dewey, Bethany, South Bethany, Fenwick Island), Delaware Bay (Broadkill, Slaughter Beach), and the Inland Bays (Rehoboth Bay, Indian River Bay, Little Assawoman Bay). Atop the county overlay, Delaware DNREC administers the state Coastal Zone Act regulated area and the Delaware Coastal Management Program (NOAA-approved CZMA program since 1979) — the CZA regulated area covers Sussex's entire Atlantic-coast and bay-shore band and governs major industrial land uses more than ADUs, but ADUs within the CZMA-mapped area still encounter DNREC review where a state subaqueous lands or wetlands permit is triggered. The Delaware Bay and Atlantic Ocean coastal band also sits within NFIP VE zones (velocity/wave action) where ADU construction requires elevation and breakaway-wall detailing. The county does NOT administer a wildland-urban interface (WUI) overlay — Delaware is not a WUI state. Historic-district overlays are handled by individual municipalities (Lewes, Rehoboth Beach, Milton, Milford, Seaford) rather than at the county level.

• Sussex County Flood-Prone Districts Overlay — Sussex County's local implementation of FEMA NFIP floodplain-management standards. FIRMs most recently updated and affirmed by FEMA 2015-03; Round Pole Branch and Clear Brook studies ongoing. An ADU within a mapped SFHA (Zone A, AE, or VE) faces elevation, venting, anchoring, and — in V zones — breakaway-wall requirements that materially change construction cost. Lowest-finished-floor must meet or exceed the base flood elevation plus any adopted freeboard.
• Sussex County Flood Map Ordinance administrative page — Administrative landing page linking the county ordinance text, the FIRM viewer, and the parcel-lookup workflow for confirming SFHA status before submitting a permit application.
• Delaware Coastal Zone Act / CZMA regulated area — The Delaware CZA regulated area spans the entire Atlantic coast of Sussex County and the Delaware Bay and Inland Bays shoreline. CZA review focuses on heavy industry and port uses — ADUs are not themselves a CZA-triggering use — but the broader CZMA consistency review applies to federally permitted actions and to state subaqueous-lands/wetlands permits that a shore-proximate ADU might trigger.
• DNREC Wetlands and Subaqueous Lands jurisdiction — State-level overlay that can affect ADU siting on tidal-wetland-adjacent parcels and on parcels extending into subaqueous lands. DNREC review is separate from county zoning review and can add 60-180 days to the permitting clock for shore-proximate parcels.
• DNREC Floodplain Management — State floodplain-management program that coordinates with Sussex County's local ordinance. DNREC maintains the Delaware Flood Planning Tool (https://floodplanning.dnrec.delaware.gov/) for parcel-level SFHA and sea-level-rise scenario lookup, which is a useful pre-application screen for ADU proposals on Sussex coastal parcels.
• FEMA National Flood Insurance Program (NFIP) participation — Sussex County is an NFIP-participating community; ADUs on parcels in V zones require engineered foundations and cannot have enclosed habitable space below base flood elevation. ADUs in A/AE zones must have elevated finished floors and flood-vented crawlspaces. Community Rating System (CRS) discounts for flood-insurance policyholders depend on the community's CRS class, which is reviewed on a 5-year cycle.