Managing Water Before It Becomes a Foundation Problem
Nearly every foundation problem in the Puget Sound region has water somewhere in its history. Saturated soil pushes harder against basement walls. Water moving through fill accelerates settlement. Sustained moisture decays crawl space framing. Runoff undermines flatwork and washes out the support beneath slabs.
Drainage work addresses the cause rather than the symptom, which makes it some of the best value in this trade. It is also the least glamorous, which is why it gets skipped in favour of something more visible, and why we raise it on nearly every Seattle foundation repair project we scope.
Puget Sound rain is the relevant condition. It is not intense, it is relentless, weeks of steady rain that raises water tables, saturates soil profiles, and finds every path that was not planned for.
What We Look At First
Downspouts and where they actually discharge. A roof sheds a lot of water. A downspout emptying at the base of a wall delivers all of it into the soil pressing against your foundation. This is the most common finding and the cheapest to fix.
Grading in the first several feet. Ground should fall away from the building. Decades of landscaping, mulch top-ups, and settled backfill frequently reverse that, creating a shallow basin against the wall.
Existing drains. Many Seattle homes have a footing drain. A meaningful proportion of those drains no longer work, having silted shut, been crushed, or lost their outlet. Whether an existing drain can be restored is worth establishing before assuming replacement.
Uphill contribution. On a sloped lot, water arriving from above can dwarf what falls on the property itself. That changes where the system should go.
The discharge. Where is water supposed to end up? Surprisingly often, the honest answer for an existing system is “into the ground about four feet from the wall,” which is no answer at all.
Footing Drains and Interceptor Drains
A footing drain runs alongside the footing at the base of the foundation wall, collecting water that has reached the building envelope and routing it away. It is the conventional perimeter system and it belongs on most excavated waterproofing scopes.
An interceptor drain sits uphill of the structure, cutting across the slope to catch water before it arrives. On the hillside lots that characterise West Seattle, Queen Anne, Magnolia, Edmonds, and Issaquah, an interceptor frequently accomplishes more per dollar than anything installed at the building.
The two are not alternatives so much as different positions in the same strategy. The footing versus interceptor drains guide sets out which conditions favour each.
Details That Determine Whether a Drain Lasts
Washed aggregate. The drainage envelope has to stay open. Aggregate with fines in it starts partially blocked.
Geotextile filter fabric. Wrapping the envelope keeps soil fines from migrating in and silting the system. Omitting the fabric is the single most common reason a twenty-year-old footing drain no longer functions, and it is also the cheapest thing on the material list.
Pipe orientation and fall. Perforations positioned correctly and a consistent gradient toward the outlet. A flat run holds water rather than moving it.
A real outlet. Daylighting to a lower part of the site where fall allows, or a tightline to an approved discharge point. Where a connection to the municipal system is being considered, Seattle Public Utilities (SPU) governs that permitting and it is a separate step from the drain design itself. Where neither a daylight outlet nor a municipal connection is available, a basin and pump, which we cover under sump pump systems.
How This Connects to the Other Work
Drainage overlaps with several other scopes and it should be planned alongside them rather than bought separately.
With basement waterproofing: exterior drainage reduces the water arriving; interior collection handles what still gets in. Which combination applies depends on the entry pathway.
With crawl space moisture control: bulk water has to be controlled before a liner goes down, and drainage is how that happens.
With basement wall repair: hydrostatic pressure is a load on the wall. Reducing it through drainage means the reinforcement is not fighting a permanent headwind.
With retaining wall repair: most retaining wall failures have blocked drainage behind them somewhere in the story.
What Drainage Does Not Do
It does not stabilise a moving slope. Reducing pore water pressure within a slope is genuinely relevant to slope behaviour and often forms part of a geotechnical recommendation, but a drain is not a slope repair and we will not sell it as one. Where the question is whether a hillside is moving, that belongs with a geotechnical engineer.
It also does not fix a structural problem that already exists. If a wall has bowed or a footing has settled, better drainage stops the driver from continuing; it does not undo the movement. Those repairs are separate scopes with separate line items.
Seasonal maintenance keeps the whole assembly working, and our foundation and drainage maintenance guide covers the checks worth doing before each wet season.
