Water that ends up in a basement usually started at a downspout

A wet basement corner is nearly always blamed on the foundation, because that is where the water appears. The water usually started thirty feet above it. A roof sheds an enormous volume during a heavy rain, all of it concentrated into a handful of downspouts, and if that concentrated flow is released at the base of the wall it will find its way in. The foundation is the symptom. Drainage is the cause, and drainage is fixable in an afternoon with a ladder and a shovel.

Fall is the right time because the leaves that will clog everything are coming down now, and because you want the system working before the freeze and thaw cycles start moving water in and out of the soil.

Clear the gutters after most of the leaves are down, not before

Cleaning in early October and again in mid November beats one heroic cleaning at the wrong time. Scoop the debris out rather than flushing it into the downspout, which is how you turn a gutter problem into a blockage you cannot reach. Then run a hose at the far end and watch the whole length.

What you are looking for while the water runs is not just flow. It is standing water, which means the gutter has sagged or was hung level instead of pitched. A gutter needs a slight fall toward the outlet, and a section holding water will eventually pull its own hangers out under the weight. Adding or resetting a hanger is a ten dollar part and ten minutes.

Follow the water once it leaves the downspout

This is the step almost everyone skips. Stand at the bottom of each downspout during or right after a hard rain and watch where the water actually goes. If it pools within a few feet of the wall, or runs back toward the house along a walkway, you have found your basement problem.

The remedies, in rising order of cost and effort:

1. Add an extension so the discharge lands at least four to six feet from the foundation, further on the uphill side of the house.
2. Set a splash block on graded soil so the water is directed away rather than allowed to soak straight down.
3. Bury a solid drain line running to daylight, if the yard falls away from the house somewhere you can get to.

Extensions get kicked off, mowed over and forgotten, which is why the check is seasonal rather than one time. A hinged extension that folds up for mowing survives longer than a straight one that has to be removed and put back.

Check the six feet of ground closest to the wall

Soil settles against a foundation for years after a house is built, and backfilled soil settles most. What began as ground sloping away can become ground sloping back without anyone noticing, because the change happens an inch at a time.

Lay a straight board on the soil running away from the wall and put a level on it. You want a fall of roughly an inch per foot for the first six feet. Where it is flat or negative, add soil rather than mulch, tamp it, and slope it. Mulch alone holds moisture against the wall and does not hold a grade. If there is a bed against the house, the bed should still fall away underneath whatever is planted in it.

Look also at what the water hits when it leaves the graded zone. A patio, driveway or walkway pitched back toward the house will undo everything you just did upstream.

The jobs to hand to someone else

Gutter cleaning on a single story is reasonable homeowner work with a stable ladder and someone holding it. Anything above one story, anything on a steep roof, and anything requiring you to lean is worth paying for, and the market rate for it is low enough that the calculation is not close. Falls from ladders are one of the injury categories the Consumer Product Safety Commission tracks, and the height at which people get hurt is lower than most expect.

Also worth hiring out: reslinging a long gutter run that has pulled away, cutting in a new downspout where the existing ones are overloaded, and any buried drain line, which needs to be pitched correctly and sleeved where it crosses under a drive.

What this prevents, and why it compounds

Water that repeatedly saturates the soil next to a foundation does several things at once. It raises hydrostatic pressure against the wall, it finds and widens existing cracks, it feeds efflorescence and mold on the inside face, and in freezing climates it expands. None of those are dramatic in a single season. All of them are cumulative, and each one makes the next cheaper for the water and more expensive for you.

Reverse it and the compounding runs the other way. A dry perimeter stays dry, the cracks stop growing, and the interior finishes stop being at risk. Two hours of gutter work and a bag of soil is an unglamorous way to protect a basement, and it is the intervention with by far the best return of anything you can do to a house this month.