Home Drainage in Washington: Gutters, Grading, and Moisture Problems
Water reaches a Washington house by three routes, and none of them is fixed the same way. It comes off the roof, through a gutter and a downspout, arriving fast at a single point. It crosses the ground, carried by a grade that falls the wrong way, a driveway, or a lot that slopes down to your wall. And it rises from the soil, as groundwater or as water held in a heavy clay that never drains.
Sort the route before paying for the remedy, then fix in the order the routes run. The roof outlet is first, because it delivers the fastest water and is the cheapest thing to redirect. The grade is second, and in Washington it is a code matter rather than a preference. The soil is last, because it is the slowest route, the hardest to see, and the only one that has to be observed in the wet season to be observed at all.
This guide maps the three routes, gives the ground-level observations that separate them, and names which page owns each remedy. It does not design a drain, size a pipe, or price any of it, and some of what it routes onward belongs to a licensed professional.
Sort the symptom before the solution
| What you are seeing | Which route it usually belongs to | What you can observe safely |
|---|---|---|
| A damp band, stain or rot at the base of a wall after rain | Roof runoff landing too close, or surface water running along the wall | Where the downspout outlet discharges, and which way the ground falls |
| Water sheeting across a patio or driveway toward the house | Surface water and the grade | The direction of fall, watched during rain |
| Erosion, a rill, or soil washed off below an outlet | Roof runoff arriving faster than the ground can take it | The outlet itself, its splash protection and the ground beneath it |
| A soft patch of lawn or planting bed that stays wet for days | Subsurface water, or a soil that drains slowly | Whether it is still soggy in mid-winter, and whether the soil is hard or loose |
| Water in a crawlspace, a basement or at a slab edge | Any of the three | Which of the observations above matches what you see |
| Water arriving from a neighbour’s ground or a slope above | Surface water coming from off the property | The direction it comes from, observed and photographed during rain |
The last row is the one people skip. Water that enters the property from uphill is not fixed by work on your own downspouts, and the observation that settles it is the same one that settles everything else here: watch it during rain, and write down where it comes from and where it goes.
The observation that costs nothing
Walk the property in the rain — not after it, and not on the first wet day. Snohomish County’s RainScaping guide asks for a few rain-drenched days before its own assessment is made, with more than half an inch of rain, or until water can be seen flowing on the property, on the grounds that a wet season shows what a dry one cannot.
Four things are worth a dated photograph and a note: where each downspout discharges and where that water goes next; where water stands on paving or bare ground, and how long it takes to leave; where the ground beside the foundation is soft, wet, or falling toward the wall; and the low corner of the property, which is where everything else arrives.
The Environmental Protection Agency puts the same check in maintenance terms: inspect the exterior grounds around a building for signs of ponding, which may indicate blockage. Standing water is evidence of something upstream of it, not a fault in the puddle.
Roof runoff: the water that arrives fastest
Roof water is the easiest route to control, because it is collected at a known place before it becomes anything else. That is the gutter’s job, and the system, its cleaning interval and its failure modes are their own subject. What matters here is the far end of it.
Snohomish County’s surface-water program states the problem plainly: water coming out of a downspout is fast-moving and can cause erosion. So every outlet is asked to have a splash block or an equivalent, the roof area draining to any one downspout is capped at 700 square feet, and downspouts are spaced 20 to 50 feet apart.
Where that water lands is the decision. On a hard surface it is on its way to the storm drain, and the storm drain reaches the nearest creek, lake or wetland untreated. The county’s own guidance is that runoff picks up what it touches — oil from the road, yard chemicals, pet waste — and carries it into streams, lakes and Puget Sound, which is why Washington treats yard waste placed near a storm drain as illegal rather than untidy.
Where it lands on the ground instead, the question is distance. The published figures do not agree, and each is written for its own program: Clark County’s downspout-disconnect program asks for at least 6 feet from the foundation, 10 feet from a retaining wall, 5 feet from the property line and 3 feet from a public sidewalk, while Snohomish County asks for a minimum of 10 feet from the foundation into a vegetated area. National guidance sits with the longer figure — the EPA asks for leaders carrying water at least 10 feet from the foundation, or to whatever more stringent local rule applies. Choosing and building that outlet is its own subject in this cluster.
Two further symptoms belong here rather than with the gutter. Water pouring over the front edge during rain while the outlet runs dry is a diagnosis of its own; an outlet that has stopped running while the gutter still discharges is checked in the downspout page; and a buried drain that has stopped accepting water needs the pipe found before it needs anything else. In winter, that same water can freeze where it is asked to move, which is its own question again, and the debris that starts the trouble off the roof belongs to the roof-care guide.
Surface water and the grade
The grade is the second route, and in Washington it is written into the code. The residential code requires provisions for the control and drainage of surface water away from the building, with the grade falling a minimum of 6 inches in the first 10 feet — the requirement Clark County’s building department publishes in its plan-review checklist as section R401.3.
The EPA arrives at the same figure from the design side: specify a 5 percent slope, which is 6 inches per 10 feet, to the finish grade away from the foundation, applied over the 6 to 10 feet nearest the building, and keep a minimum of 8 inches of foundation exposed after final grading. Two consequences follow for a household. A grade that falls toward the house is not a cosmetic fault, because it delivers every drop that lands on it to the place the roof water is also trying to avoid. And a slope that has settled, or been lost under a new bed, a raised border or a pile of bark, can undo something that was correct when it was built.
Ground cover belongs to the same route. Snohomish County’s runoff guidance is that bare soil and slopes are vulnerable to runoff — without vegetation, leaf litter or mulch, those areas erode and produce more of it — and that runoff from slopes directed toward structures can destabilize foundations or create damp crawlspaces and basements.
Where a slope, a wall or a lot line leaves less room than the rule wants, the fall cannot simply be made steeper. That situation needs a designer and the jurisdiction’s own requirement, and it is not work this page will describe.
Subsurface water: what the soil does after the rain stops
The third route is the slow one, and the one a dry-season inspection cannot find.
Washington’s wet season sets the observation window. Snohomish County’s site-evaluation guide states that groundwater is usually closest to the surface from December through April, and asks owners to dig a 12-inch-deep hole where they are considering an infiltration solution, note whether the soil is soft or hard, and, if water is present in the hole, measure from the ground surface down to the water. That measurement is the seasonal groundwater level, and the guide’s warning about it is the useful part: during the dry times of the year you may not observe this characteristic of the soils at all.
Whether that water can leave is a soil question. The Rain Garden Handbook for Western Washington, published by the Snohomish Conservation District with state funding and carried as a state publication, sets the test: dig a test hole to the intended depth, fill it with water, and record how far the level falls per hour. Clay feels sticky and smooth and drains slowly; sand feels gritty and drains quickly. Where groundwater rises to within a foot of the surface in winter, the handbook states that an infiltration feature will not drain or function properly at all.
Below ground, the building carries its own provisions. The residential code requires drains around foundations that retain earth and enclose habitable or usable space below grade — section R405.1, as the same county checklist states it — and the EPA describes what such a system does: a coating on the below-grade wall that keeps out the water saturating the surrounding fill, free-draining gravel or a drainage mat held against the wall, and a footing drain at the bottom carrying rainwater and groundwater away from the footing and the slab. The same guidance asks for the interior floor of a basement or crawlspace to sit above the local water table, which is the reason a wet-season diagnosis matters to a decision made in a dry month.
Where the ground beside the foundation is not being drained at that level, the work is not a household repair. Water appearing inside is the last symptom to arrive and the first to escalate, because it can be a roof, a wall, a grade, a drain or the ground itself. The useful order is to find the source outside before spending anything on the inside.
What an infiltrating solution depends on
The common answer — let it soak in — has requirements before it has a size. Under Washington’s stormwater rules, a rain garden must have a minimum horizontal surface area below its overflow that is at least 5 percent of the area draining to it, which for a 1,000-square-foot roof is 50 square feet of feature before any ponding depth is counted. Three things come before that number: a drainage-rate test in the right season, a groundwater observation, and the setbacks.
The handbook puts a feature at least 10 feet from a building foundation, to keep water out of basements and crawl spaces, and at least 5 feet from utilities; 100 feet from a drinking-water well; and 50 feet uphill or 10 feet downhill of a septic system, with the local health department’s requirement controlling. Snohomish County’s guide adds the same well and septic distances, and the instruction to look up a septic system’s as-built record before digging or stockpiling anywhere near it. Neither document grants a general permission to infiltrate: both tie the answer to the soil under the specific feature and to the local program’s rules.
Washington’s two climates change the timing, not the order
The state does not have one drainage season. WSU Extension puts Puget Sound at about 40 inches of rain a year with less than an inch in some summer months, Spokane and Pullman at about 20 inches with a dry June, July and August, and the arid south-central part of the state at about 9 inches.
West of the Cascades, the wet season delivers months of low-intensity rain to soils that are saturated through the winter, which is why the two county programs read here are written for that climate, and why the diagnosis is made in the middle of the wet season. East of the mountains, some of the same water arrives against frozen ground with snow load behind it and leaves as melt, and the EPA’s own design checklist asks the designer to state the assumed maximum rainfall or snowmelt rather than only one figure. The order in which the three routes are checked does not change across the state; only the season in which the third one can be seen does. The seasonal plan the checks belong to is its own guide.
Before you dig anywhere
Nothing here should be dug before the ground has been located, and in Washington that is a legal duty rather than advice. The state’s underground utilities chapter requires an excavator, before commencing any excavation, to mark the boundary of the excavation area with white lining or white pins and then give notice to all facility operators through the one-number locator service, with a work-to-begin date not less than two full business days ahead. The rain garden handbook reduces the whole thing to one line: call 811 before you dig.
Two documents are worth having in hand first: the local health department’s as-built record for a septic system, and any drainage plan the jurisdiction holds for the property, which is also where the rule about what may be discharged lives.
Where the work stops
Everything this guide asks a reader to do is observation and a phone call: watch the rain, measure the fall, note the outlets, look up the records, and call the locate service before any digging.
The physical remedies are not in this page’s scope, and several situations leave the household’s own judgement entirely — a slope or retaining wall that has moved, movement near a steep slope, a foundation showing cracking or settlement, water arriving inside the building, or anything within a septic system’s reserve area. The rain garden handbook’s own advice for a feature within 50 feet of a slope steeper than 10 percent is to consult a geotechnical engineer, and the same instinct applies to anything that looks like ground movement rather than water.
Two further questions are local-government questions rather than construction ones. What may be discharged to a storm drain, a ditch or the ground is set by the authority that owns the receiving water, which is why Clark and Snohomish counties answer it differently; wash water from pressure washing or house washing is a category of its own, with its own disposal rules. Water that has already arrived inside is a diagnosis before it is a repair.
Next step
Walk the property once in the next rain and once on a dry day, and write four things down with dates and photographs: where each downspout discharges, where water stands on paved or bare ground, where the ground beside the foundation is soft or falling inward, and the low corner of the lot. Those four notes decide which route you are dealing with, and they are the evidence a professional conversation will ask for. Then work upstream — the roof outlet first, the grade second, the soil last.