Crawlspace Water After the Patio Regrade

Cause ranking, and why the order is not negotiable:

1. Water is being delivered to the house on purpose. A 4% slope over 25 ft moves about 12 inches of fall in the wrong direction, straight at the foundation. No amount of dry well or fertilizer fixes that; it must be reversed first.
2. Roof water is concentrated at the wall. 1,100 sq ft of roof on splash blocks 8 inches out is a designed infiltration pit against the foundation.
3. The surface layer is the wrong material. Gray clay with slickensides is excavation spoil, not topsoil: it is dense, dispersive, shrinks and swells, and at 0.1 in/hr it accepts almost nothing.
4. Only then do you get to plants and fertility. Fertilizing turf on a site that ponds is money into a symptom.

Grading standard to build to: the ground surface must fall a minimum of 6 inches within the first 10 feet away from the foundation, with positive fall continuing away from the structure. On this lot that means a rebuilt swale along the rear wall, daylighted to an approved discharge, not a flat lawn. Also:

• Extend downspouts to discharge at least 5 ft from the foundation, onto splash blocks or into tightline, graded to fall away.
• Keep the finish grade at least 6 inches below any siding or sheathing.
• Check the crawlspace itself: vapor barrier lapped and sealed, no debris, and confirm whether the source is surface water or a rising water table.

Document the existing grade with elevations before you touch it - the report becomes your defense if the homeowner later blames your work for a pre-existing condition.

Volume: 1,100 sq ft × 0.623 gal/sq ft per inch of rain = 685 gallons = 91.6 cu ft of water for a 1-inch storm.

In 1½-inch-minus drain rock at roughly 40% void space: 91.6 ÷ 0.40 = 229 cu ft of rock. A 4 ft diameter × 4 ft deep dry well holds about 50 cu ft, so you would need 4–5 of them just for a 1-inch storm, and they would still have to drain out between storms.

Will it drain? Essentially no. At 0.1 in/hr, a pit with, say, 50 sq ft of effective infiltrative surface accepts about 5 cu ft per hour - roughly 37 gallons. Discharging 685 gallons into it means the pit stays full for many days, backs up the roof drain, and saturates the same clay that is already failing. A dry well is a good tool in sandy soil and a bad tool in slickensided clay.

What to install instead:

• Tightline the downspouts to a graded swale or to the municipal storm system if the jurisdiction allows the connection, or to a daylight discharge point on the lot where the water can leave the site.
• If no daylight exists, use a surface swale plus a shallow vegetated conveyance with 2% fall to a low point away from the house, and consider a sump and pump only as a last resort.
• If the client insists on infiltration, get a real percolation test at the proposed location and design to it - do not guess.

Point to make to a client: infiltration is a soil property, not a product. The contractor's job is to test before selling the device.

Remove and rebuild, don't amend in place. The 5 inches of spoil clay comes out, not into the soil.

Specification:

1. Strip and remove the clay layer to subgrade; do not rototill it into anything. Do not work the subgrade wet - smearing clay at field capacity creates a plow pan that takes years to undo.
2. Scarify the subgrade to 2 inches and relieve any compaction from the patio equipment (this is likely the real reason the low corner ponds).
3. Place imported topsoil 6–8 inches deep: sandy loam with 5–8% organic matter, pH 6.0–7.0, screened, tested. At 6 inches over 1,000 sq ft = 500 cu ft = 18.5 cu yd loose.
4. Compost incorporation if using native soil as a base instead: 2–3 cu yd per 1,000 sq ft tilled into the top 6–8 inches.
5. Finish grade to the swale and the 6-inches-in-10-feet fall, then roll lightly, not compact hard. Target bulk density under about 1.4 g/cc at the surface.
6. Turf: install sod or seed a tall fescue/perennial ryegrass blend appropriate to western Oregon; tall fescue tolerates the wet-winter/dry-summer pattern better than fine fescue in a lawn that must be walked on.
7. Fertility: the soil test (pH 6.1, 2.1% OM) does not call for lime or a rescue fertilizer program. Apply a starter at seeding/sod time and one fall application; fix drainage and organic matter first, then retest in a year.

Warranty language: exclude ponding caused by the swale being blocked or by the client regrading; hand over the finished grade elevations.