The Short Answer
Commercial roof drains and scuppers fail mostly from debris, ice, and worn flashing where the membrane meets the drain. Michigan's plumbing and building codes require secondary overflow drains or scuppers wherever a parapet would trap water if the main drains clogged, with overflow discharging where people will see it. Clear drains at least twice a year and after storms, keep strainers in place, and have leaks at drain flashings repaired by a roofer trained on your membrane.
Key Points
- Under the 2021 Michigan Plumbing Code, secondary overflow drains or scuppers are required where parapets would trap water if the primary drains backed up (Section 1108.1).
- Overflow discharge has to be above grade where occupants or maintenance staff would normally see it, so water pouring from an overflow scupper is a warning that primary drains are blocked.
- Each inch of water standing on a roof adds about 5.2 pounds per square foot, which is why codes design roofs for the depth water reaches with primary drains blocked.
- Most drain leaks are at the flashing between the membrane and the drain bowl, a loose clamping ring or a missing strainer, not in the pipe.
- Staff who clear scuppers at the roof edge are within 6 feet of it, where MIOSHA's adopted federal rule requires fall protection.
How a Flat Roof Drains
Interior roof drain
Primary
A cast iron or plastic drain body set in the deck, with a clamping ring that grips the membrane, and a dome or flat strainer on top to keep debris out. It connects to leaders and storm piping inside the building.
Scupper
Primary or overflow
An opening through a parapet or edge, lined with metal and flashed into the membrane. Primary scuppers usually drain into a conductor head and downspout; overflow scuppers sit higher and discharge straight out.
Secondary (overflow) drain
Backup
A separate drain set higher than the primary, often with a raised dam ring, or a separate overflow scupper. It only flows when water rises above the primary system's normal level.
Gutters and downspouts
Edge drainage
Common on smaller low-slope buildings without parapets. In Michigan they take ice and snow loads and often fail at the seams and hangers.
Crickets and tapered insulation
Moving water to the drain
Built-up slope that steers water toward drains and away from walls and curbs. Without it, water sits between drains.
What Michigan's Codes Require
Commercial buildings in Michigan are built under the Michigan Building Code, which LARA's rule R 408.30401 bases on the 2021 International Building Code, and the Michigan Plumbing Code, which rule R 408.30701 bases on the 2021 International Plumbing Code. The building code says roof drainage design and installation must comply with its own Section 1502, its rain load section 1611, and Chapter 11 of the plumbing code.
The core rule is secondary drainage. Section 1108.1 of the plumbing code and Section 1502.2 of the building code require secondary (emergency overflow) roof drains or scuppers where roof drains are required and the roof perimeter extends above the roof so water would be trapped if the primary drains backed up. Where primary and secondary drains come as one assembly, each must have its own inlet and outlet.
Section 1108.2 requires the secondary system to discharge separately from the primary, above grade, "in a location that would normally be observed by the building occupants or maintenance personnel." Section 1108.3 sizes secondary drains on the same rainfall rate as the primary system without counting any flow through the primary, and says overflow scuppers must have an opening at least 4 inches high.
Two more details matter on repairs. Section 1105.1 says roof drains must be installed per the manufacturer's instructions and the inside opening must not be obstructed by the roofing membrane. And Section 1101.7 requires roofs to be designed for the maximum depth of water that could pond on them with all primary drains assumed blocked.
LARA has proposed moving the Michigan Plumbing Code to the 2024 IPC; a public hearing was scheduled for 5 August 2026. Confirm the current edition with your building department before design work.
Why Blocked Drains Are a Structural Problem
Water is heavy. At about 62.4 pounds per cubic foot, each inch of water standing on a roof weighs about 5.2 pounds per square foot. A few inches spread across a large roof bay is many tons of load, and as the deck deflects under it, more water collects in the low spot.
That is why Section 1611.1 of the Michigan Building Code designs roofs for rainwater that accumulates with the primary drainage blocked, plus the water rising above the secondary drain inlet at its design flow, and Section 1611.2 requires susceptible bays to be checked for ponding instability. The secondary system sets the maximum depth. If the overflow is blocked too, or was never installed, nothing limits it.
Michigan winters add snow and ice to the same roof. A clogged drain in November can leave a sheet of ice that holds the next storm's meltwater, and snow drifts against parapets and rooftop units, exactly where scuppers and drains often sit.
Why Drains and Scuppers Fail
- Debris: leaves, seed fluff, gravel, nesting material and wrappers from rooftop service calls pack strainers. A missing strainer lets debris into the leader, where it is much harder to clear.
- Flashing at the drain: the membrane is clamped into the drain bowl. Loose or missing clamping ring bolts, split membrane at the bowl and old sealant let water run down the outside of the drain body into the building.
- High drains: a drain that sits higher than the surrounding roof, because of deck sag or added insulation, leaves a ring of standing water around it.
- Ice: exterior downspouts and conductor heads freeze solid in Michigan winters; scuppers ice over; thaw-and-refreeze cycles back water up against the membrane.
- Scupper corners: the inside corners of a scupper box are hard to flash, and sealant there is maintenance, not a permanent seal.
- Overflows blocked or mis-set: an overflow scupper stuffed with debris, or an overflow drain set at the same height as the primary, does not provide the backup the code intends.
A Drain Maintenance Routine That Works
- Step 1
Inspect Spring and Fall, and After Storms
Mule-Hide's building owner guidelines call for roof inspections at least twice a year, spring and fall, and after every major storm. In West Michigan, time the fall visit after most leaves are down and before the first hard freeze.
- Step 2
Clear Strainers and Put Them Back
Remove debris from every drain, scupper and gutter, and reinstall strainers and domes. A drain without its strainer is the next clog.
- Step 3
Check the Overflows
Look at every overflow scupper and drain. If you have seen water coming out of one, the primary drains were blocked during that storm.
- Step 4
Look at the Flashing and Clamping Ring
Note splits, open laps or loose bolts at drain bowls and scupper boxes. These are repairs for a roofer trained on your membrane.
- Step 5
Watch for Water 48 Hours After Rain
Mule-Hide's guidelines say good practice is not to let water remain on the roof more than 48 hours after a rain. Photograph any that does.
- Step 6
Keep a Log
Record dates, what was cleared, who accessed the roof and what they did. Manufacturers ask for this, and it helps trace damage later.
Mule-Hide's guidelines also warn against using any asphalt product to repair a single-ply membrane, because it will degrade the membrane. Use only products the membrane manufacturer approves.
Rooftop Safety for Maintenance Staff
Clearing a scupper means working at the roof edge. Michigan's general industry rule on walking-working surfaces (R 408.10202) adopts the federal OSHA standard, 29 CFR 1910 Subpart D, by reference.
That standard sets distances for work on low-slope roofs. Within 6 feet of the edge, each employee must be protected by a guardrail, safety net, travel restraint or personal fall arrest system. From 6 to 15 feet, the same protection applies, though a designated area may be used for work that is both infrequent and temporary. At 15 feet or more, the employer must provide protection or a designated area, or may skip fall protection for infrequent and temporary work, and must enforce a rule keeping workers from going within 15 feet of the edge unprotected.
In practice, many owners keep staff to interior drains well back from the edge and leave scuppers, gutters and edge work to a roofing contractor equipped for it. Skylights are another hazard on flat roofs; keep people away from them.
Repair Options for Drains and Scuppers
Clear and restore strainers
Maintenance
Remove debris, flush the bowl, reinstall or replace missing strainers and domes. If water still backs up, the blockage is in the piping, which is a plumber's job.
Re-flash the drain
Most drain leaks
Remove the clamping ring, cut out deteriorated membrane around the bowl, install new membrane or a target flashing per the membrane manufacturer, and reset the ring with all bolts. The opening must stay clear of membrane, as Section 1105.1 requires.
Lower a high drain
Ponding around the drain
Tapered insulation or a drain sump around the drain so water flows into it rather than around it. Often combined with crickets between drains.
Rebuild a scupper
Leaking scupper box
New metal scupper box and fresh membrane flashing into the parapet, sized to match the original or the design requirements.
Add or correct overflows
Design work
Adding secondary drainage involves sizing, structural and permit questions. Section 1512.1 does not require secondary drains to be added when an existing roof with positive drainage is re-covered or replaced, but a building with ponding or no overflow at all deserves a design review.
Drains and Your Manufacturer Warranty
Commercial membrane warranties put drainage on the owner. A Mule-Hide single-ply system warranty, for example, excludes defects in the building, pre-existing conditions or roof design, including any conditions that prevent positive drainage, and excludes damage from the owner's or occupant's failure to use reasonable care in maintaining the roof. It also says Mule-Hide is not obligated to perform additional services such as roof drains.
The same warranty requires written notice to Mule-Hide within ten days after the owner discovers a leak, and says notice to the contractor is not notice to Mule-Hide. Alterations or repairs on or through the roof without Mule-Hide's prior written authorization can make the warranty cancelable. Read your own warranty's notice and authorization terms before anyone works on a drain.
Stellar is a Mule-Hide contractor for flat and low-slope roofs and a GAF CoatingsPro contractor for silicone coatings, and our commercial maintenance programs are built to keep manufacturer warranties in force with documented periodic inspection.
When a leak is already happening
Triage, protecting tenants and inventory, and documenting for the warranty.
Commercial roof leak action planDrainage Components: What Fails and Who Fixes It
| Component | Common Failure | What to Check | Usually Fixed By |
|---|---|---|---|
| Drain strainer or dome | Missing, broken, packed with debris | Present, secured, clear | Maintenance staff or roofer |
| Drain flashing and clamping ring | Split membrane, loose bolts, open laps | Membrane at the bowl, all bolts tight | Roofer certified on the membrane |
| Leader and storm piping | Blockage below the bowl, cracked pipe | Water backing up with a clear strainer | Plumber |
| Primary scupper and conductor head | Debris, ice, open corners | Clear opening, sound corners | Roofer; sheet metal for the head |
| Overflow scupper or drain | Blocked, set too low, missing | Clear, higher than primary, discharge visible | Roofer, with design review if adding |
| Gutters and downspouts | Ice damage, open seams, loose hangers | Seams, hangers, outlets | Gutter or sheet metal contractor |
Stellar handles the roof side of drains and scuppers: membrane, flashing, scupper boxes, tapered insulation and crickets. Storm piping is a plumber's work, and gutters are another trade.
Drains Backing Up or Leaking?
Our commercial inspection is free. We check every drain, scupper and overflow, document what we find with photos, and put repair options and a maintenance plan in writing. Mihles Pena holds Haag Commercial certification.
Related Guides
Ponding Water on Flat Roofs
The 48-hour rule, causes and repair options.
Learn MoreCommercial Roof Inspection Schedule
Twice a year, after storms, and what the report should include.
Learn MoreCommercial Roof Leak Action Plan
What property managers should do when water comes in.
Learn MoreFlat Roof Repair
How we repair membrane, seams, drains and flashing.
Learn MoreQuestions We Hear
Are overflow scuppers required on a flat roof in Michigan?
Where roof drains are required and parapets or other perimeter construction would trap water if the primary drains backed up, yes. The 2021 Michigan Plumbing Code (Section 1108.1) and Michigan Building Code (Section 1502.2) require secondary overflow drains or scuppers. Replacing or re-covering an existing roof with positive drainage does not by itself trigger adding them (Section 1512.1).
Why is water coming out of my overflow scupper?
Because water on the roof rose above the primary drains' level, which usually means the primary drains or their piping are partly blocked. The code requires overflow discharge where occupants or maintenance staff will see it for exactly this reason. Have the primary drains and strainers checked soon, before the next heavy rain.
How often should commercial roof drains be cleaned?
At least at the spring and fall inspections and after major storms, which matches Mule-Hide's owner guidelines. Buildings under heavy tree cover, near cottonwoods or with frequent rooftop service traffic may need more frequent checks. In West Michigan, time the fall cleaning after the leaves are down.
Who fixes a leaking roof drain, a roofer or a plumber?
If water is getting in around the drain where the membrane meets the drain bowl, that is roofing work: re-flashing and resetting the clamping ring. If the drain is clear at the top but water still backs up, or the pipe below is cracked or leaking, that is a plumber's job. A careful inspection tells you which.
Can I add a drain to fix ponding on my flat roof?
Sometimes, but adding a drain means new storm piping inside the building, structural considerations and usually a permit. Many ponding problems are solved instead with tapered insulation, crickets or a drain sump that moves water to the existing drains. A roofer and, where needed, an engineer or plumber should look at it together.
What This Page Cites
- 2021 Michigan Plumbing Code, Chapter 11 Storm Drainage, Sections 1101.7, 1105.1, 1106.1 and 1108.1 to 1108.3, International Code Council (https://codes.iccsafe.org/content/MIPC2021P1/chapter-11-storm-drainage), accessed October 2026
- Mich Admin Code R 408.30701, Applicable code (Michigan Plumbing Code adopts the 2021 IPC), Legal Information Institute, Cornell Law School (https://www.law.cornell.edu/regulations/michigan/Mich-Admin-Code-R-408-30701), accessed October 2026
- 2021 Michigan Building Code, Chapter 15 Roof Assemblies and Rooftop Structures, Sections 1502.1 to 1502.3 and 1512.1, International Code Council (https://codes.iccsafe.org/content/MIBC2021P1/chapter-15-roof-assemblies-and-rooftop-structures), accessed October 2026
- 2021 Michigan Building Code, Chapter 16 Structural Design, Sections 1611.1 and 1611.2, International Code Council (https://codes.iccsafe.org/content/MIBC2021P1/chapter-16-structural-design), accessed October 2026
- Mich Admin Code R 408.30401, Applicable code (Michigan Building Code adopts the 2021 IBC), Legal Information Institute, Cornell Law School (https://www.law.cornell.edu/regulations/michigan/Mich-Admin-Code-R-408-30401), accessed October 2026
- Currently Open Rules (Construction Code Part 7, Plumbing Code; proposed 2024 IPC adoption), Michigan Department of Licensing and Regulatory Affairs, Bureau of Construction Codes (https://www.michigan.gov/en/lara/bureau-list/bcc/rules-acts/rules/currently-open), accessed October 2026
- Premium Single-Ply NDL System Warranty (Ver. 4.0) and Building Owner's Roof Care and Maintenance Guidelines (ver. 7), Mule-Hide Products Co., as filed with the City of Steamboat Springs (https://cityview.steamboatsprings.net/Portal/Permit/GetFile/35379), accessed October 2026
- Mich Admin Code R 408.10202, Adoption of federal standard (29 CFR 1910 Subpart D), Legal Information Institute, Cornell Law School (https://www.law.cornell.edu/regulations/michigan/Mich-Admin-Code-R-408-10202), accessed October 2026
- 29 CFR 1910.28(b)(13), Work on low-slope roofs, Electronic Code of Federal Regulations (https://www.ecfr.gov/current/title-29/subtitle-B/chapter-XVII/part-1910/subpart-D/section-1910.28), accessed October 2026