Why your basement only leaks during spring melt

A basement that leaks in a July downpour and a basement that leaks in a March thaw are usually two different problems. The seasonal one is more common in Edmonton, it is easier to diagnose, and homeowners tend to ignore it for years because it goes away on its own by May.

It goes away because the water stops. Not because anything got fixed.

What makes melt different from rain

Rain arrives and drains. Melt arrives into ground that cannot take it. The top of our soil stays frozen well after the snow starts going, so meltwater has nowhere to go but sideways across the surface and down the one gap that is always thawed first: the strip of soil right against your heated foundation wall.

That strip is warmer than the rest of the yard all winter. Every spring it becomes a channel that runs straight down the outside of your wall to the footing.

The four causes, in the order we find them

1. Snow piled against the house

Shovelled walkways and driveways have to go somewhere, and the somewhere is usually the flowerbed against the wall. That pile is measured in hundreds of litres and it releases all of it into the worst possible spot over about a week.

2. Negative grading you cannot see under the snow

Edmonton clay settles. A lot that was graded correctly when the house was built often slopes back toward the foundation twenty years later. In summer it is subtle enough to miss. In March it collects the entire yard.

3. Weeping tile that only fails under load

Partially clogged weeping tile handles a normal week fine and gets overwhelmed by melt. That is why the leak is seasonal. Your drainage is not broken, it is undersized for the one week of the year that matters.

4. A crack that opens in the cold

Concrete contracts in the cold. A hairline crack that is closed tight in August can be measurably wider in February, and it closes back up as the wall warms. Homeowners often report a leak that appears and then cannot be found later.

How to tell which one you have

Where the water shows up narrows it fast.

Water at the joint where the floor meets the wall, along a length of wall rather than one spot, points at weeping tile or groundwater. Water running down the face of the wall from a visible line points at a crack. Water near a window points at the well. Water in more than one place along the same wall points at grading above that wall.

Take photos the day it happens. By the time anyone can excavate, the evidence is gone.

What to do before the next melt

Move snow away from the foundation as you shovel. Two metres of clearance is enough to matter.

Extend downspouts so they discharge at least two metres out, and make sure the end is not buried in a snowbank. A downspout draining into a drift beside the wall is worse than no extension at all.

Check the slope in the fall while you can see the ground. You want the soil dropping away from the wall over the first two metres. Fixing it is soil and labour, not construction.

Test your sump pump in February, before you need it. Pour a bucket into the pit and watch it start, empty and shut off.

What the repairs cost

Grading and downspout work is the first thing to do and the cheapest by a wide margin. Crack injection runs $1,200 to $2,000 for a single crack. Interior drainage and a sump runs $120 to $250 per linear foot. Exterior waterproofing runs $300 to $400 per linear foot and is the option that keeps water off the wall entirely rather than managing it once it arrives.

Anyone who quotes excavation before looking at where the water enters is selling, not diagnosing.

What to do next

If you had water this spring, the work to prevent next spring happens in summer and fall while the ground is workable. Waiting until March means waiting another full year.

Send us a photo of where the water appeared and we will tell you which of the four causes it looks like, at no cost.

Related reading: why window wells fill with water and the fall freeze-up checklist.

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