How to keep a Seattle basement dry through the rainy season

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• GuideHow to fix grading, downspouts and window wells to stop a wet basement

  Most wet basements are fixed outside, with a shovel and some downspout pipe. The sequence that works: make the gutters catch the roof water and carry it at least 5 to 6 ft from the wall, regrade so the soil falls 6 in. in the first 10 ft, then give every window well a cover and a drain. On the wet-basement calls we ran, those three jobs stopped the water more often than anything sold for the inside of the wall. Here is how to measure each one, do the work in a weekend, and read the sump pump and the hygrometer afterward to prove it worked.

• GuideBasement waterproofing checklist: gutters, grading, window wells and sealing, in that order

  Before anyone sells you an interior drain system, spend a Saturday on the outside of the house. Most of the wet basements we were called to were roof and lot problems: a downspout dumping at the corner, soil that had settled toward the wall, a window well with no drain. The fixes cost less than the estimate for the drain tile, and the checklist runs in the order water travels: gutters and downspouts first, grading second, window wells third, then cracks and sealers, and only then the interior drain, sump and dehumidifier. Here is the walk-around with the measurements, what each interior fix can and cannot do, and the point at which the pro systems are the right call.

• GuideWhat humidity should a basement be, and how to measure it

  Thirty to fifty percent relative humidity, measured in the middle of the room at chest height, is the target; the EPA's guidance is to keep indoor humidity below 60 percent and ideally between 30 and 50. Basements miss it for a physical reason, not a mysterious one: the same air that reads 50 percent upstairs reads 70 percent in a basement that is ten degrees cooler, and 100 percent on a cold slab. Here is how to measure it so the number means something, what the seasons do to it, and how to tell a basement that needs a dehumidifier from one that is taking on water.

• Best picksThe best dehumidifier for a basement

  For most basements, buy a 50-pint (DOE 2019) portable and run it on a hose to a floor drain; the Midea Cube 50 is our pick because its 4-gallon bucket and app make it the easiest to live with. If the only drain is uphill, buy the Frigidaire FHDP5033Y1 with its built-in pump. If you want a conventional box with a published spec sheet, the Frigidaire FHDD5033Y1; if the basement is small and only musty, the 20-pint Cube.

• GuideHow to test a sump pump, and how often

  Fill the pit with a hose or a bucket until the float lifts, watch the pump start, empty the pit and stop, listen for the check valve to close without water rushing back, and go outside to see water leave the discharge. That is the whole test, and it takes five minutes. Do it monthly and before any forecast storm; Zoeller's own instructions call for a check at least every three months and Wayne's say three to four times a year. The failures that flood basements are quiet ones, a stuck float or a seized impeller, and a pit that fills on a dry day is the only test that finds them before the storm does.

• GuideHow to winterize pipes: the checklist, and when heat cable makes sense

  Burst supply lines from freezing were the most expensive residential water losses we dried, and nearly every one started at a pipe the owner knew was exposed: a hose bib with the hose still on, a run through a crawl space with the vents open, a line in a garage wall. Winterizing is an afternoon in October: hoses off and bibs drained, irrigation blown out, exposed runs sleeved and air leaks sealed, heat cable on the few runs that need it, and a cold-snap routine of open cabinet doors, a dripping faucet and a thermostat that never drops below 55°F. This is the list in the order water freezes, with the manufacturer and CPSC rules for heat cable and what to do if a pipe freezes anyway.