Most commercial roof bills trace back to a drain that did not work. Water that cannot leave the roof sits on it, loads it and finds the weakest seam. A roof in Coeur d'Alene sheds its snowmelt through the same few openings every thaw, and the city rates local weathering as severe. If one of them is packed, frozen or set too high, the membrane pays for it.
A drain fix is among the cheapest line items on a roof. A ponding fix that ignores the drain is among the most expensive. We price both the way they should be priced: cleaning, resetting and re-sloping as separate options.
The Call: Clean, Reset or Re-Slope
There are three levels of fix, and each has a different bill. Cleaning clears the strainer, the bowl and the line, and it is the right answer when the drain is the right size and in the right place but plugged. Resetting lowers or replaces a drain body or sump that sits above the low point, so water can enter it. Re-sloping adds tapered insulation or a cricket to move water to the drain, and it is the right answer when the roof is flat where it should fall.
We tell the owner which level the roof needs, and we do not sell the expensive one when cleaning will do.
The walk that decides it is short. We look at where the water goes after a rain, at the stains and dirt lines that mark the edge of old ponds, and at whether the membrane has algae or grit rings where water stood. Dirt rings are a map. They show the pond even when the roof is dry, and they show how far it spreads when the drain stays shut. We mark them on the plan and tie each one to the nearest drain. A drain that still backs up after cleaning has a line problem, and we flag it for a plumber rather than guessing.
What It Costs: Water Is Heavy
Standing water is not just a leak risk. A foot of water weighs more than 60 pounds per square foot, so a pond on top of a snow load can eat a large part of the margin built into the structure. That weight is why ponding correction is a structural line item as well as a waterproofing one. A pond of two inches over a bay is a load that has no business being there, and in January it can freeze into a plate of ice that blocks the drain for good.
The costs split cleanly. Cleaning is an hourly or per-drain price. A reset is a per-drain price plus flashing and membrane work around it. Adding an overflow scupper is a per-opening price with flashing, liner and sometimes a downspout. Re-sloping with tapered insulation is a per-area price and sits with the rest of the insulation and cover board scope. A GC pricing a reroof can carry the drain work as a bid alternate, since drains are cheapest to correct when the roof is already open.
What the Code Sheet Says: Overflow Is Not Optional
The snow number shapes the drain plan more than any other line on the city sheet. If a primary drain clogs, an overflow must pass the water before the roof becomes a basin. Idaho enforces the 2018 International Building Code statewide, and secondary drainage is part of how that code treats low-slope roofs with parapets.
A drift pocket behind a parapet is a block of weight sitting beside the drain, and it is heaviest when the snow is saturated. We count every drain and scupper, measure the area each serves and compare the result to the building plan. A roof with one drain doing the work of three is a ponding bid waiting to happen.
Where It Fails First: Sumps, Screens and Scupper Edges
Failures start small. A screen gets packed with grit blown up from the lot. A sump silts up and the bowl no longer pulls water. A scupper edge cracks, and meltwater runs behind the liner. A downspout freezes at the base, and the whole line backs up to the opening. In Coeur d'Alene's freeze and thaw cycles, a drain that is half open in the morning can be closed by evening.
We check the strainer, the clamping ring, the membrane flashing at the bowl, the sump depth and the pipe below. For scuppers we check the liner, the opening size and the downspout. A scupper that spills onto a walk or an entry gets a downspout or a splash block, because ice on a sidewalk is a liability. Our preventive maintenance visits clear drains in fall and check them in spring, and the ponding water repair scope picks up where cleaning leaves off.
Alternates: Heat Trace, Crickets and Overflows
Several upgrades fit as alternates. Heat trace at a sump or scupper keeps the opening from icing in a cold snap. A cricket behind a rooftop unit or at a curb sends water around the obstruction. An overflow scupper above the primary drain gives the roof a safety path. A larger scupper opening keeps a skin of ice from sealing it. Each is a separate line with a price, so the owner decides what stays.
Snow behavior drives the choice. A roof near the lake or in Post Falls, where snow averages about 59 inches a year, needs the extra capacity sooner than one in a drier place such as Spokane Valley, which gets just over 16 inches of annual precipitation. In the Silver Valley, where Wallace averages about 76 inches and Mullan over 100, we assume the heavier load and plan drains accordingly. A downtown Coeur d'Alene building with a parapet roof and interior drains has different needs from a tilt-up at Riverbend Commerce Park with scuppers through the wall.
Closeout: A Drain Log the Owner Keeps
At closeout the owner gets a drain log. Each drain and scupper is numbered on a roof plan, with a before and after photo, the date, what was done and what was found. Over time the log shows which drains clog fastest, which freeze first and where an overflow would help.
That log is useful for a GC taking over a building, a lender asking about condition and an insurer reviewing a claim. It also makes the next decision easy: if one drain has needed cleaning at every visit, it needs a bigger fix. The log is the argument for the bid alternate, with the evidence attached.
Commercial Roofing Questions
How often should drains be cleaned?
Twice at minimum, once ahead of the first snow and once after the last thaw. Roofs near trees or lots may need a third pass.
Is ponding always a problem?
Water that stands for more than a couple of days after rain or melt is. It loads the roof and shortens membrane life. We find the cause and price the fix.
Do I need an overflow scupper?
On a roof with parapets, yes. If the primary drain clogs, an overflow passes the water before it floods the roof.
Can heat trace prevent frozen drains?
It helps at a sump or scupper that ices up. It does not replace cleaning and does not fix a drain that is set too high.
What if the drain still backs up after cleaning?
The pipe below has a blockage or a bend. We flag it for a plumber and document the test.