Keeping The Drains Clear
The highest-value half hour on a Toronto commercial roof is the one spent clearing the drains in November.
Short answer
Clear every drain, strainer, scupper and overflow after leaf fall and before the first freeze, and again in spring. Record what you found. A blocked drain going into a Toronto winter turns snowfall into standing water, then into ice, and the load becomes a structural question rather than a drainage one.
The routine
Every primary drain, with the strainer lifted and the throat checked rather than just the grate looked at.
Every scupper through the parapet, including the far side.
Every overflow drain and overflow scupper, which are the things nobody clears because they are not normally in use.
The roof field, particularly against parapets, curbs and equipment where debris collects and then migrates to the drain in the first storm.
Internal downspout access points and cleanouts where they exist.
And the discharge at ground level, because a blocked bottom backs the whole system up.
Lift the strainer
A drain that looks clear from above frequently has a plug of debris just below the strainer, in the throat. Lifting the strainer and checking the throat is the difference between a drain that looks fine and a drain that works. It takes a minute per drain.
The winter behaviour
Snow melts from the underside against a warm roof and the meltwater reaches the drain.
If the drain is blocked or frozen, that meltwater ponds, then refreezes, and the cycle repeats.
An internal drain in a cold chase or an exterior downspout freezes more readily than the drain itself.
An iced-over scupper is the same problem with no visible warning.
Which is why the overflow provision matters: it is the route out when the primary is frozen, and it has to be clear too.
And why a mid-winter check after a thaw-freeze cycle is worth doing on a building with history.
What to record
A roof plan with every drain, scupper, overflow and downspout route marked. This makes every subsequent visit faster and the next leak much easier to trace.
What was found at each one, dated, with photographs.
Any standing water or ponding area, with its location.
Any damage found to the membrane, the flashing or the equipment supports.
The date of each visit, because an insurer after a loss will ask for the maintenance record.
And a note of anything that needs a repair visit, so it is scheduled rather than remembered.
Common questions
How often should commercial drains be cleared?
After leaf fall before the first freeze, and again in spring.
Why lift the strainer?
Because the plug of debris is usually in the throat below it, not on top.
Do overflows need clearing?
Yes. They are the route out when the primary drain is frozen.