Short answer
In dry PNW summers, expansive clay soils lose moisture and shrink away from footings—soil desiccation. That volume loss removes support, so walls can settle unevenly, rotate, or crack. When fall rains return, water floods the new gaps and raises pressure against the foundation.
Dive deep
The deciding mechanism is soil volumetric change relative to footing support. When moisture drops below plastic limits, soil shrinks and leaves gaps under footings. On site we measure perimeter gaps, track vertical/stair-step cracks that widen in dry months, map tree roots pulling moisture from footing zones, check differential floor elevations, and compare footing depth to the active drying zone.
“Just pack topsoil into the gap” does not restore support under the footing. Fall rains then expand that fill and can drive sharp lateral pressure into the wall. Settlement needs structural underpinning or engineered repair—not surface dirt packing.
When it applies
- Extended dry spells on high-clay sites
- Mature trees drawing deep moisture near the home
- Footings not anchored into stable non-shrink strata
When it does not
- Foundations on dense glacial till, bedrock, or well-engineered gravel beds that do not shrink/swell with moisture
What we do next
If summer drying has opened cracks or settlement, see how we stabilize footings through our Seattle foundation crack repair and foundation repair services.
