Last reviewed October 31, 2026.
The first warm weekend in April, you walk the yard and find the same soft spot by the back corner of the house, right where the downspout ends. The basement wall on that side shows a damp line again. The neighbor mentioned that in heavy rain, water crosses the lawn toward their driveway.
Nudging the downspout a few feet will not settle it. The real question is where your roof water is allowed to go.
What the codes say about roof water
Start with state law. Section 507.1 of the 2025 Property Maintenance Code of New York State says roof drainage shall not be discharged in a manner that creates a public nuisance. Towns and villages fill in the rest.
The Town of North Hempstead’s plumbing article, Section 2-43, exempts houses of two and a half stories or fewer from its own gutter requirement. A 2014 amendment says leaders in residential zones may be drained to the surface, rain barrels, dry wells or a combination of them.
The Village of Muttontown spells out more. Section 144-5 bars roof water from flower beds or planting areas next to a foundation, and says leaders should not sit at a corner of the house, patio, walkway or driveway where there is or might be a drainage problem. Massapequa Park’s runoff rule is on our Massapequa Park permit guide.
Towns that ask for a dry well, and when
Most of these triggers come with new building, not a gutter swap.
- Huntington. The town’s Stormwater Management Program Plan, revised March 2026, says a building permit for a residential expansion is conditioned on drywells that capture the runoff from a 3-inch storm.
- Brookhaven. Section 81-6 requires some additions in the town’s wetlands jurisdiction area to install drywells for a 2-inch rainfall from the entire house, including the addition and paved areas.
- Riverhead. Section 229-13 calls for dry wells of adequate capacity where roof runoff will cause erosion or drainage problems for adjoining properties.
- Babylon. The town’s building permit checklist includes roof drains connected to dry wells, as our Babylon permit guide explains.
- Muttontown. Where a dry well is required, it must hold 2 inches of rainfall at 100 percent runoff.
The Town of Oyster Bay’s site plan rules are summarized on our gutter installation cost guide. For permits by town, see our Long Island roofing permits hub.
Turning a storm depth into gallons
The codes name a rainfall depth, not a tank, so the conversion falls to you. It is plain arithmetic. One thousand square feet of roof under 2 inches of rain is about 167 cubic feet of water, or roughly 1,250 gallons. Under Huntington’s 3 inches the same roof gives about 250 cubic feet, close to 1,870 gallons. “One hundred percent runoff,” Muttontown’s phrase, means every square foot of roof counts, with nothing assumed to soak in on the way.
A few codes reach down into the well itself. Muttontown requires at least a 2-foot-diameter grate or a solid cast-iron cover. Roslyn’s stormwater chapter caps dry well depth at 25 feet and keeps wells at least 10 feet apart, wall to wall. The roof area that feeds each downspout is the same number used to size the gutter, worked through on our gutter sizes guide.
How far from the house and the lot line
Muttontown’s Section 144-4 puts dry wells at least 10 feet clear of property lines and 20 feet clear of building foundations. On a lot too small for that, an engineer can certify in a sealed letter that a shorter distance will not harm the building.
North Hempstead’s Section 70-202.2 points to Nassau County drainage standards, then lets 20-foot distances drop to 10 feet on lots of insufficient size. Going shorter takes a letter from a New York licensed architect or engineer. The Village of Sands Point is stricter on the lot line. Its Section 74-7 keeps site subsurface drainage structures at least 25 feet from any property line.
For an addition or renovation to a Suffolk single-family house, the county health department’s application (form WWM-057, revised August 2017) asks for proposed drywells, storm drains and all drainage structures to be shown on the plan, along with every part of the sanitary system.
Splash blocks, extensions and rain barrels
Not every downspout has to go underground. Muttontown says that when dry wells are not required, leaders with an elbow discharge onto concrete splash blocks. The blocks are designed to carry water away from the foundation and spread it out so the soil does not erode. North Hempstead lists rain barrels as an accepted outlet in residential zones.
How far an extension should carry the water is something local installers publish; our gutter repair page has their figures. Between them, the North Hempstead, Muttontown and Riverhead codes boil down to two limits. Roof water should not damage the foundation. And it should not become the neighbor’s problem.
Keep roof water out of the sewer
The Village of Farmingdale’s Section 454-9 bars anyone from discharging roof runoff into a Nassau County sewer facility. North Hempstead adds the reverse rule: no plumbing fixture may drain into a stormwater drywell. If an old leader dives into a pipe you cannot trace, have a plumber find where it ends before any new drainage goes in. Then match the downspouts to the gutters, which our gutter installation page covers.
