Valley soils and seasonal movement
Modesto sits in the San Joaquin Valley, and soil conditions vary across the area. Some soils contain clay that swells when wet and shrinks when dry; others are sandier and drain quickly. Seasonal moisture changes are a common driver of foundation movement: soils wet up in winter, when most of the year's rain falls and tule fog keeps the ground damp, and dry out through long, hot summers.
The signs of seasonal movement include doors that stick in one season and not another, cracks that open and close, and floors that seem slightly out of level at certain times of year. Keeping soil moisture around the foundation more even reduces that movement.
Irrigation and foundations
Modesto homes often have extensive lawn and landscape irrigation. Sprinklers that spray foundation walls, broken lines near the house, and planting beds that are soaked repeatedly can saturate soil at the foundation. On the other hand, letting soil next to the foundation dry out completely in summer and then soaking it causes swelling and shrinking. Aim irrigation away from the house, fix leaks promptly and keep moisture moderate and consistent.
Modesto's drinking water comes from a mix of treated Tuolumne River water and city groundwater wells. A plumbing leak under a slab or near a footing, from either the supply or the drain line, can wash out soil or cause it to swell. If you notice a rising water bill, warm spots on the floor or damp areas near the foundation, have the plumbing tested.
Slab and raised foundations
Many Modesto homes sit on slabs; older homes often have raised foundations with crawlspaces. In crawlspaces, look for standing water, damp soil, wood decay, sagging girders and posts that have shifted. In slab homes, cracked tile, sloping floors and drywall cracks above doors are common signs.
Trees
Large trees near the house can draw moisture from soil near foundations during summer. Before removing a large tree near the house, ask a foundation professional about the potential effect on soil moisture.
Drainage basics
Clean gutters, downspouts extended well away from the house, and soil graded to slope away from the foundation are inexpensive protections that prevent many problems.
Before you hire
Ask Modesto foundation contractors what's causing the movement, whether they measured floor elevations, which repair method they recommend and why, whether the plumbing should be tested first, and whether an engineer and permit are involved. Look up the contractor's California license with the CSLB.
Tracking cracks
Mark the ends of a crack with a pencil and the date, photograph it beside a ruler, and check monthly. A year of records shows whether movement is seasonal or ongoing, and gives a contractor or engineer something concrete to work with.
Additions and garage conversions
Additions and converted garages are common in Modesto, and they're often built on footings that differ from the original house. Where old and new meet, cracks can open if the two parts move differently. An inspection should look at the whole structure, including where additions connect.