Forty-Two-Lot Preliminary Plat with Floodplain and a Long Cul-de-Sac
An engineer submits a 42-lot preliminary plat for a 38.5-acre parcel in a Michigan township. Zoning requires 15,000 sq ft minimum lot area, 80-ft width, 30-ft front setback, 10-ft side, and 30-ft rear. The parcel has 1,200 ft of frontage on a paved county road, 8.2 acres of 100-year floodplain along a creek, and 3.1 acres of regulated wetland. The plan shows a 5.0-acre park, a 2,500-ft-long cul-de-sac street, and 6 lots entirely within the floodplain. The county drain commissioner requires on-site detention for the 2-year storm. The township's review must consider the Michigan Land Division Act and local ordinance. The developer wants to keep 42 lots and asks whether the floodplain can be counted as lot area and whether the cul-de-sac length is acceptable.
1. Calculate the net developable area and determine whether 42 lots can meet the 15,000 sq ft minimum. State assumptions.
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Gross equals 38.5 ac, or 1,677,060 sq ft. Floodplain is 8.2 ac, wetland is 3.1 ac, and the park is 5.0 ac. Assume a 66-ft county road right-of-way: 1,200 times 66 equals 79,200 sq ft, or 1.82 ac. Assume a 60-ft internal street: 2,500 times 60 equals 150,000 sq ft, or 3.44 ac. Total streets equal 5.26 ac. Net upland after removing floodplain, wetland, park, and streets equals 38.5 minus 8.2 minus 3.1 minus 5.0 minus 5.26, or 16.94 ac. Forty-two lots at 15,000 sq ft equal 630,000 sq ft, or 14.46 ac, leaving 2.48 ac. On paper, 42 lots fit if floodplain and wetland can be counted inside lot areas and if all lots have buildable upland. But 6 lots are entirely in floodplain and are not buildable; removing them leaves 36 lots, or 12.42 ac, leaving 4.52 ac. The plan must also meet lot width, setbacks, and buildable-area rules. Conclusion: 42 lots is not supportable as drawn; 36 lots is more realistic, and even that requires a buildable-area analysis.
2. Identify the major plat-review issues beyond lot area.
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Issues include: (1) six floodplain lots-local ordinance may prohibit residential construction or require the lowest floor above the flood protection elevation; (2) wetlands-EGLE permit and buffer, and no disturbance without approval; (3) the 2,500-ft cul-de-sac likely exceeds the local maximum and may fail emergency-access requirements; (4) detention-the drain commissioner requires on-site storage for the 2-year storm, and the plan does not show a detention area; (5) the park-5.0 ac is 13% of gross, which may exceed the required dedication; confirm whether the township wants cash in lieu or a different location; (6) county road access permit and sight distance; (7) Land Division Act procedures-tentative preliminary plat, utility plans, and approvals; (8) lot width and setbacks, especially on cul-de-sac bulbs.
3. Recommend a redesign that the developer can take to the township.
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Reduce to about 36 lots and use the floodplain and wetland as common open space, not as building lots. Shorten the cul-de-sac to the local maximum or provide a loop or emergency access; place detention in the open-space area and show the 2-year storm routing. Keep the park at the required dedication or negotiate cash in lieu. Show buildable envelopes outside floodplain, wetland, and buffers. Provide a preliminary stormwater plan, utility plan, and traffic and emergency-access justification. Confirm the Land Division Act and local ordinance standards before filing. The developer should not argue that floodplain 'counts' as lot area; it may count mathematically but not as buildable area, and the six floodplain lots will not pass review.