Ice dams, downspouts and Detroit's drainage charge

Michigan State's extension service describes it plainly: ice dams form when attic heat warms the roof and melts the snow, the meltwater runs down under the snow and refreezes at the eaves — the coldest part of the roof — and the ice that builds up there dams the water behind it until it backs up under the shingles and into the attic, the ceilings, the walls and the insulation (the extension article).

Its answer is one sentence: the underlying problem leading to the formation of ice dams is undesirable attic heat, and either too little insulation or too little ventilation in the attic is generally the cause. It adds that attic insulation should not extend over the soffit or eave area, because that keeps the eaves warm and blocks the soffit vents that let cold air in, and that there should be enough inlet vents in the soffit as well as outlet vents at or near the peak.

The article does not use the word “gutter” once. New gutters and guards will not stop an ice dam. The service's own temporary measures are raking the snow off the eaves or heat tape to melt the ice, and it warns those may not prevent a dam higher up if the attic is too warm.

The city requires a permit before work starts to recover or replace a roof, and the requirements it publishes for that work are the ones aimed at this problem.

• Ice and water shield at the eaves, from the edge to a point at least 24 inches inside the exterior wall line. That requirement exists because of ice dams.
• Attic ventilation of 1/150 of the space ventilated, maintained.
• Any rotted wood removed and replaced.
• Two inspections — one at the tear-off and one at the end. The city says to call the buildings division at 313-224-3202 24 hours in advance and no later than 3 p.m. to schedule one.

All of it from the city's roof replacement and recovery requirements (PDF). This is the honest reason a gutter conversation sometimes turns into a roof conversation, and it is also the reason to be suspicious of anybody who answers “ice dams” with “guards.”

Detroit bills drainage separately from water, and the amount is based on hard surface: your drainage fee is based on the actual amount of hard surfaces on your property that send rainfall and snow melt into the sewer system (DWSD). The roof is one of those surfaces. The published rate is $768.75 per impervious acre per month from July 1, 2026 (the rate card (PDF)), and the city's own sample residential bill — five units of water, a family of three, a 5/8-inch meter and 0.05 impervious acres — puts the drainage line at $30.51 a month (the city's cost breakdown (PDF)). Properties with less than 0.02 impervious acres are not billed at all.

Then the part that belongs to gutters: residential properties receive an automatic 25% green credit on their bill based on the assumption they have redirected their downspouts to run onto their lawn instead of directly into the sewer (DWSD). It is automatic for residential accounts; non-residential accounts have to apply.

So the credit is already on the bill of a house whose downspouts still run into the sewer. That is what makes this a gutter question rather than a billing one.

If the hard surface on your bill looks wrong, DWSD's own instruction is to fill out the drainage charge adjustment application or call a customer care representative at 313-267-8000, and to check the parcel first in its impervious surface viewer: go to the viewer, enter your address, view your parcel information (DWSD). That number is the city's, for a billing question — not ours, and not for a gutter.

The city's drainage guide states it this way: Detroit residents are required by state law to disconnect downspouts leading to the combined sewer system, therefore residential properties that do not have disconnected downspouts may lose all or a portion of the automatic credit in the future (the guide (PDF)). That sentence is the city's; the guide itself cites no law.

The instruments behind it are two, and they do different things. Michigan law requires the state to make downspout disconnection a condition of Detroit's combined sewer discharge permit, which is a duty on the regulator and on the city (the statute). The rule that applies directly to a homeowner is the city's own sewer ordinance, which since 1979 has barred connecting roof downspouts, foundation drains or other surface runoff to a building sewer that reaches the public sanitary sewer (the ordinance).

On permits the city is unambiguous, and it is good news: a permit is not required to perform downspout disconnections for residential customers. Non-residential customers are told to contact the buildings department at 313-224-2733 for current requirements, and any other city, state or federal permitting still applies (the guide (PDF)).

The city's guide is specific, and the specifics are what a contractor should be quoting to.

• Onto well established grass or other plantings that soak water in. Not onto a driveway or a walkway, and not onto bare, compacted or poorly vegetated soil.
• At least five feet from the structure. The guide also recommends a five-foot downspout extension.
• At least fifteen feet of flow path from the end of the downspout to the property line or the next hard surface.
• On ground falling less than one foot over twenty.
• Never so that it floods, ices, or runs onto the street or a neighbor's property. The caption under the guide's own “NO!” diagram is about stormwater running down the driveway to the street: the discharge can also cause an icing hazard.

From the city's drainage program guide (PDF), pages 1 and 2.

Three feet or five? The city's own documents disagree. The drainage guide says discharge five feet from the structure. The city's basement backup protection program scopes the same work as “disconnect downspouts and install extensions at least three feet from foundation” (the program), and the state's rehabilitation standard says downspout outlets will be a minimum of three feet from the foundation (the standard (PDF)). A contractor should be working to the longer one.

The city publishes the steps: measure about nine inches above where the downspout enters the storm drain and cut there with a hacksaw; work out whether the pipe left in the ground is bell-shaped or straight; a bell gets a chicken-wire cup, crumpled newspaper and concrete finished flush with the top of the bell, and a straight pipe gets capped — in most cases, a rubber cap secured by a hose clamp may be used; then the downspout goes into an elbow, secured with a screw or a rivet, with a five-foot extension recommended to carry stormwater away from foundations, sidewalks and driveways, and a splash pad optional (the guide (PDF)).

That is the city's description, not an instruction from us, and not a job we pass on: the downspout work we refer is an extension or reattaching one. The part people get wrong is the pipe left in the ground: an open, uncapped sewer connection beside the foundation is worse than the downspout was. The city's own closing caution is the other one — it is critical to ensure that the disconnected downspout does not cause a hazard or nuisance to neighboring properties.

Above ground, an extension is $5 – $20; buried, the same downspout is $150 – $350 for a run capped at ten feet, including the trench, a catch basin, drainpipe and a bubbler (national ranges).

The weather service recorded widespread three to five inches of rain across Metro Detroit that weekend, locally six to eight, with major flooding in Wayne and Washtenaw (the weather service's event page). Its own three-day gauge totals are the reason to distrust any single “Detroit” rainfall number: 8.19 inches at Grosse Pointe Park and 8.00 at a gauge south of the city, against 4.30 at Detroit City Airport and 1.75 at Detroit Metro — a spread of more than four times inside one county.

An independent review commissioned afterwards put the heaviest areas above six inches, some above eight in 24 hours, and calculated a rainfall return period of 200 years to over 1,000 years. It records that the city received thousands of reported water-in-basement complaints and publishes no count (the executive summary (PDF)). Across Michigan, federal individual assistance for that two-day disaster was approved for 56,531 households, totaling about $197 million (the federal open data record) — a state figure, not a Detroit basement count.

When the city then spent flood money on Detroit houses, it started with Victoria Park and Aviation Sub, the neighborhoods hit hardest, and 382 backwater valves went in during phase 1. Item two on that program's scope of work was disconnecting downspouts and installing extensions at least three feet from the foundation (the program).

Applications for phases 1 and 2 are closed, and the city says they will reopen only if additional funding is received. The city's standing advice on the same page is that property owners should disconnect downspouts from the sewer system and, where necessary, install a backwater valve or a sump pump.

The city's flooding handbook names it: one of the most common causes of water pooling up against a home is failure to maintain functioning gutters and downspouts. If those roof drainage systems fail, or freeze-up in the winter, they can cause all water from the roof to drain right beside the house and seep along the foundation wall and possibly into the basement (the handbook (PDF)).

Its own homeowner list puts it three ways: clean gutters regularly, because clogs let rainwater seep down the wall and into the foundation; disconnect downspouts from the sewer and redirect the runoff onto the lawn; and regrade dirt and mulch so the ground slopes away from the house.

That is a maintenance list, not a sales pitch, and most of it is free. When the gutters themselves are past maintenance, what a replacement costs is on the cost page, and one gutter contractor who serves Detroit can come and measure.