Where To Point Your Downspouts?

Should gutters / downspouts connect to NYC sewer?

Author

Nick Nyhan
April 30, 2024 • Estimated Reading Time: 11 minutes

Photo from the frontlines (is this even legal anymore)?

[❗️ Note: Updated August 2024 to reflect further input from two experts: a private-sector engineer who works with the city and knows the Unified Stormwater Rules well, as well as a senior DEP official.]

In 2023, it rained every 3 days on average according to the NYC DEP. In fact, New York City is now designated a “sub-tropical” climate by NOAA.

With all that rain, the boring old gutter and downspout plays an important role at key moments. So where your gutters and downspouts release the water can have a big impact in helping us manage city flooding.

  • Example: a developer just built a new 4 story condo building near me and said his downspouts had to connect to a catch basin system buried under gravel in the backyard.  He said it was a new requirement.

Now you may have your gutters directly connected to the sewer, as do a lot of us. And it made sense in the past….but now the NYC sewers are quickly over capacity. (More on that below.)

So to help prevent overloading the sewer system, the city and the DEP changed the rules in what is called the Unified Stormwater Rule Update 2022.

It is a dense and kind of technical document seemingly meant more for engineers, plumbers, and architects.

But I read through it with a ”regular guy”point of view looking for rules related to smaller buildings and homeowners. Then I asked some experts about it. Here is my take:

Q: What is the Unified Stormwater Rule meant to do?

A: Redirect, reduce or at least slow down water going into NYC sewers all at once.

A key quote from the DEP website on this rule: “changing requirements for how stormwater is managed on all new and redevelopment sites that discharge to City sewers…..setting new thresholds for compliance and a new retention-first approach for design.”

Note: I highlighted the “new and redevelopment sites” part because that was a key detail for people who are in older smaller buildings. Read on…

Q: As a smaller building owner with downspouts already connected to the city sewers, am I still okay?

A: Yes, still okay and you do NOT need to submit for a DEP review…unless you check certain boxes.

There is no need to submit your downspout connection for DEP approval in existing 1-3 family building, unless:

  • You are doing work that expands your impervious surface by over 200 square feet (see below for more on that)

  • OR your changes make your building larger than 5000 sq feet

  • OR your project proposes a new sewer connection

  • OR your architect and/or DOB requires a “House Connection Proposal”

This interpretation was basically was re-affirmed for me recently by two smart people: one who is an engineer familiar with Unified Stormwater Rules AND two is a DEP official to whom I asked this question.

It is further supported here in the NYC Stormwater Manual page 22.

> “Do these rules apply to a one- or two-family house?

> Response: Yes, IF they require a site or house connection per Chapter 31 or meet the definition of a covered development project under Chapter 19.1. ”

Q: What is the detail on 200 sq feet of impervious surface?

A: If 200 sq feet or under, it seems you are good as is. If over 200 sq feet, you may need DEP review.

> “DOB Chapter 11 1101.2.1: Increases in existing impervious surfaces. Whenever impervious surfaces on the lot ARE increased, such impervious surfaces shall drain into a storm sewer system, or a combined sewer system, or to an approved place of disposal.

> “Exception: An existing one- or two-family dwelling where the area of a proposed horizontal building enlargement plus any proposed increase in impervious surfaces in total is LESS than or equal to 200 square feet (19 sq m). In such cases, the storm water discharge may be accommodated by existing facilities.”

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Q: Can outside surface changes or larger interior renovations trigger this?

A: No.

According to the NYC Stormwater Manual page 21: “Activities that do not disturb soils, such as interior renovations, and surface markings of paved areas, are not considered in the estimation of disturbed areas (requiring stormwater permitting).”

Q: How can we reduce the backups caused by stormwater water hitting our sewers so quickly?

A: While the city is working on sewer upgrades, there are things we can do with our downspouts.

1) Rain Barrel

They can be connected to your downspout with a diverter that fills the barrel first (55 gallons) and when it is full, it re-directs the water to where it went before (like the sewer).

Sounds like a drop in the bucket, but if a lot of NYC people did them, it would help.

That is why the city is giving them away because they can help slow the water down at key moments.

Downspout with Rain Barrel Diverter

Rain barrel holds first 55 gal and then the rest goes to sewer

More on rain barrels:

  • How fast will it fill? It's common for about 1/8" inch of rain to fall each hour during a moderate rainstorm. That means that a 500 square foot roof can fill a properly installed 50-gallon rain barrel in about one hour.

  • Rain barrels are great for gardens, but should only be used for non-potable (non-drinking) purposes. Or you can just empty them out on drier days.

2) Redirect downspout to a better area / system

If you are lucky enough to have a yard area with some natural features and potential absorbency - or even if you have a cement patio - there are ways to use that area.

For those with a yard and a tight budget, consider diverting some of your downspout stormwater out there, away from sewers AND away from your foundation AND your neighbors. (At least 10-15 feet away from any buildings and property lines).

A basic approach if have absorbent areas, shoot that water 10-15 feet away from your foundation and a neighbors building.

But even hard cement patios can be made more absorbent with techniques ranging from adding natural absorbent gardens to porous cement to catchment systems.

We wrote about one homeowner who installed a dry-well system under their patio (see “QuickPool” story here.) They connected downspouts from the roof and diverted a lot of water to these tanks.

Talking to a landscaper, design-build firm or architect can help you assess the specifics of your place, what your stormwater runoff is likely to be in a 1-inch storm, and come up with various options for you.

The point is take some water and slow it down: we need to help the city - and help each other - by diverting some of the growing volume of water away from our old sewer system. The downspout may seem like a small piece, but across the city it channels millions of gallons every storm.

Q: Why should we care if downspouts connect to the sewer system?

A: Because it was not built to handle this much water and when jammed, it floods where we live.

NYC sewers are estimated to handle up to 1.5 inches of rainfall per hour, but in some areas like Gowanus BK it takes less than 0.5 inches of rain to cause raw sewage getting pumped into the canal and harbor.

  • 60% of NYC uses combined sewers where: “a single pipe or a “combined sewer” to carry the flow of wastewater and stormwater to the local wastewater treatment plant.”

  • 40% of NYC uses separate sewers where: “separate pipes carry wastewater and stormwater. The pipes for wastewater connect directly to the wastewater treatment plant for further processing, while the pipes for stormwater connect directly to local waterways.”

  • Source: NYC DEP

Q: Should we just point our gutters and downspouts onto the sidewalk or street?

A: Not if you can do it another way.

Because that can lead to increased pollution and trash being swept up by the water AND it will just end up hitting the city sewers again, adding to the burden and cause more flooding.  “NYC is faced with increasing challenges from managing stormwater runoff from impervious surfaces,” says the NYC Stormwater Manual.

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