Carroll County discusses cluster subdivision rules, citing Mineral Hill example and calls to clarify open-space rules

Staff members and county commissioners used a Sept. 1 work session to review Carroll County’s cluster‑subdivision rules and a specific example project, Mineral Hill, and to flag several areas for code clarification and possible changes.

Staff member Chris opened the session by framing clustering as an established tool that groups homes to preserve open land: “Cluster development is not a new concept,” he said, noting the county has allowed cluster subdivisions since 1965. Planning staff member Daphne then reviewed definitions and code provisions in the Freedom Community Comprehensive Plan and the county subdivision regulations.

Why it matters: Commissioners said current practice departs from what many residents expect from the county master plan and from older local precedent. Several asked staff to return recommended code edits that would make open‑space requirements, the method for calculating allowable lot yield, and the limits on minimum lot sizes clearer and harder to reinterpret over time.

Key facts and the Mineral Hill example - Mineral Hill is a 9.2‑acre parcel in the Freedom District zoned R‑20,000. Staff showed the arithmetic used in the example: 9.2 acres ≈ 400,752 square feet; divided by the R‑20,000 district minimum (20,000 sq ft) produces a theoretical maximum yield of 20 lots. - The applicant’s conventional plan laid out 15 lots; the submitted cluster plan showed 14 lots. Under current county rules the cluster subdivision did not increase the permitted number of dwelling units. - Because the developer reduced some individual lot sizes below the R‑20,000 minimum, the code required the developer to provide a calculated amount of common open space equal to the aggregate lot‑size reduction. For Mineral Hill staff calculated a required open‑space amount of 53,101 square feet and the submitted plans showed about 131,990 square feet of open space (counting stormwater facilities), exceeding the minimum requirement. - County code allows counting stormwater management areas as open space; for Mineral Hill staff said the planning commission discussion treated the engineered stormwater facility as separate but the total open space still exceeded the minimum.

Open space and active open space Daphne told commissioners that the county’s code distinguishes open space (which can include forest, wetlands and stormwater areas) from active open space (designed for recreation and generally limited to gentle grades). Current county minimums include a general common‑open‑space floor (15% of gross acreage in residential/heritage districts) and an active‑open‑space requirement equal to 10% of the required open space or 1.5 acres, whichever is greater; for parcels smaller than 10 acres the planning commission may approve deviations.

Commissioners pressed staff on whether the county’s written definitions in the Freedom Comprehensive Plan and the subdivision code align with what residents expect. Commissioner Krebs and others argued that counting steep slopes, streambeds or large stormwater ponds as the bulk of a subdivision’s open space does not match the plan’s emphasis on recreational or community amenities. Daphne and Chris said those are policy choices the board can change by revising the code.

Gross vs. net developable acreage; historical changes Multiple commissioners raised the recurring issue of whether the county should calculate allowable lot yield from gross acreage (total parcel area) or net developable acreage (parcel minus floodplain, steep slopes, rights‑of‑way, stormwater areas and other non‑buildable features). Staff said the governing code was revised in 2022 so that yield is determined by gross acreage and a minimum clustering lot size floor was set (e.g., an R‑20,000 parcel cannot cluster to less than 10,000 sq ft lots). Prior to that, staff said, developers were asked to prepare conventional plans that demonstrated net developable yield and, in some earlier years, the county required percolation (perc) tests to validate conventional lots.

Commissioners who spoke from the Freedom District said that many recent subdivisions have used clustering as the norm and that, when combined with counting steep slopes and stormwater basins in the open‑space total, the resulting open land often does not provide usable recreational amenities for residents. Staff acknowledged that interpretation and practice have evolved and said the board can direct staff to change the code to rely on net acreage or tighten open‑space definitions.

Stormwater, ownership and maintenance Planning staff described county policy: when subdivisions create stormwater management facilities in residential subdivisions the county generally accepts ownership of the stormwater facilities rather than leaving long‑term management to homeowner associations (HOAs). Staff explained that policy grew from past experience in which small HOAs lacked the funding or capacity to maintain large stormwater infrastructure and the county had to step in during retrofit or NPDES (National Pollutant Discharge Elimination System) projects.

HOAs and fees Staff said Mineral Hill’s draft covenants call for an initial HOA fee of about $250 per year; the draft covenants and final HOA structure remain the developer’s responsibility during buildout. Commissioners highlighted residents’ concerns about ongoing HOA costs, reserve studies and long‑term maintenance obligations for common areas.

Cost and public‑sector maintenance impacts Staff provided an estimate (derived from the Mineral Hill contractor’s bonding figures and comparative assumptions) that building a conventional plan on that parcel could cost roughly $800,000 more to the developer than the chosen cluster layout; conversely, a conventional layout would lengthen public road mileage and increase county operations and maintenance (O&M) costs (staff estimated roughly $5,000/year for additional roadway in the Mineral Hill hypothetical). Staff and commissioners also discussed that placing stormwater underground typically raises capital and long‑term repair costs compared with surface facilities.

Process and next steps At the end of the session staff said they will compile the items discussed and return a short list of potential code and policy changes to the board. Staff proposed bringing recommended topics to the board for direction, then to the planning commission for public discussion and any ordinance drafting; that process would include public hearings before final board action. Several commissioners asked staff to include proposals that would (a) tighten open‑space definitions so that a larger share is active and usable; (b) reconsider whether yield should be calculated on net developable acreage in certain zoning districts; (c) review the minimum cluster lot size floor and whether clustering is being used as de facto rezoning; and (d) consider placing more requirements on developer proposals at the pre‑submittal stage so community expectations are clearer earlier in the process.

Closing note No new ordinance was adopted at the session. The board directed staff to prepare a concise list of options and to return with recommendations for next steps toward possible code amendments or clarifying guidance for planning commission review.