Whether or not downpours are getting heavier, one intense storm is enough to expose every weakness in a neglected eavestrough. Here is the water maths, where clogged gutters fail first, and a short before-and-after routine for Southern Ontario storms.
In This Article
The water maths behind a downpour
One millimetre of rain on one square metre of roof is one litre of water. That simple rule shows why storms hit gutters so hard. Take a roof section of 40 m² (about 430 sq ft) draining to a single downspout. If 25 mm of rain falls on it in an hour, it sheds about 1,000 litres, or roughly 17 litres a minute. In a shorter burst, the flow is higher.
This is an illustration, not a local statistic. It does show that one downspout can face a serious flow, and that a trough half-full of debris has far less room to carry it. A clear run passes that water. A blocked one turns it into overflow.
Where neglected gutters fail first
- Overflow at corners and valleys. Water spills over the front lip and lands beside the foundation. Repeated soaking of the same strip of soil is how basement seepage starts.
- Weight on the hangers. A litre of water weighs a kilogram. A trough holding several buckets of wet leaves and standing water pulls on its hangers, and fasteners in soft fascia let go first.
- Backwash behind the trough. When a trough fills faster than it drains, water can run back over the top edge and into the fascia and soffit, where it stays damp.
- Blocked outlets and split downspouts. Debris dams the outlet. Water pools behind it, adds weight, and later freezes in the pipe.
- Erosion below the drip line. Mulch washes out, a trench forms, and splash-back stains the wall and soaks the brick.
How to spot gutter damage shows what each of these looks like after the storm has passed.
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Three storm types, three different stresses
| Storm type | What it stresses | Weak point it finds |
|---|---|---|
| Summer thunderstorm | A short, intense flow that tests capacity | Partial clogs, undersized downspouts, valley overshoot |
| Long autumn rain | Steady volume on troughs full of wet leaves | Blocked outlets and saturated soil beside the house |
| Late-winter thaw with rain | Meltwater and rain on frozen ground | Ice in downspouts and outlets, and ground that cannot absorb water |
Rainfall differs from year to year, so treat these as patterns rather than forecasts. Check the Environment Canada forecast and any warnings before a storm, and again the morning after.
Before the storm: fifteen minutes on the ground
Do not climb a ladder in wind or wet weather. Most of what helps can be done with your feet on the lawn.
- Walk the house and clear leaves and grit from around each downspout outlet and extension.
- Make sure every extension is attached and pointing away from the foundation. The downspout extensions guide explains how far to carry the water.
- Clear window wells and any drain grates near the walls.
- Check that a hose still runs freely through the downspouts you can reach from the bottom.
- Move stored items away from basement walls, in case water does find a way in.
If a clean run still overflows in a hard rain, the trough or the number of downspouts may be too small for that roof. Test with a hose first, because blockage is far more common than undersizing. The eavestrough sizing guide explains when a bigger trough is the answer.
After the storm, and when to call
Wait until the roof edge and the ground are dry, then look before you touch anything. Note overflow marks on the siding, fresh trenches in the soil, drips at joints, runs that now sag, and downspouts that have pulled loose. Photograph anything wrong, with the date. If water in the basement has risen above the outlets, the furnace or the electrical panel, the Electrical Safety Authority says not to enter it, and to call your electrical utility.
Neglected gutters do not fix themselves after a storm. A clean now is cheaper than a repair later, and improving drainage around your home covers the ground side of the problem. D&D Home Services carries $2 million in general liability insurance, and its crew members are Working at Heights certified. Its gutter cleaning starts at $125 for a typical Kitchener-Waterloo home, quoted in writing before work begins.
Key Takeaways
- One millimetre of rain on one square metre of roof is one litre, so a single downspout can face a large flow in a short storm.
- Overflow, heavy wet debris and blocked outlets are where neglected gutters fail first, and each one damages the fascia, soil or foundation.
- Summer thunderstorms, long autumn rains and late-winter thaws stress gutters in different ways.
- Clear outlets and extensions from the ground before a storm, and inspect for overflow marks, sags and loose downspouts afterwards.
Sources & References
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