Much of the Los Angeles basin sits on clay soil that swells when it gets wet and shrinks when it dries out. After a long dry summer, the first heavy rains can cause noticeable movement. Good drainage is the cheapest foundation protection there is, and fall is the right time to check it.
How clay soil moves a house
Expansive clay can change volume as its moisture content changes. When one side of a house gets much wetter than the other, the soil under that side swells or softens unevenly. The foundation follows, and the result is cracks, sticking doors, and sloping floors. The goal is not dry soil. It is soil that stays at a steady moisture level all around the house.
Rainy season checklist
- Clean the gutters so water flows to the downspouts instead of spilling over the edge next to the foundation.
- Extend the downspouts so water lands several feet away from the house, or ties into an area drain.
- Check the grade. Soil should slope away from the house. Planters and walkways that slope toward the walls send water straight to the foundation.
- Look at the irrigation. Sprinklers that spray the foundation or drip lines right against the wall keep one side of the house wetter than the rest.
- Clear the drains. Area drains and catch basins clog with leaves and soil over the summer.
- Check the crawl space after the first big storm for standing water or damp soil.
- Watch large trees close to the house. Roots can dry out the soil on one side during the summer.
A quick test during the next storm
Walk around the house with an umbrella while it is raining. Watch where the roof water goes and where it puddles. Ten minutes in the rain will tell you more than any inspection on a sunny day.
When drainage is not enough
If the foundation has already moved, drainage improvements stop the cause but will not reverse the damage. Persistent cracking, sloping floors, or water in the crawl space after you have corrected the drainage are signs it is time for a structural evaluation.
Building new? Plan drainage from day one
For new homes, additions, and ADUs, a soils report, proper footing design, and a drainage plan prevent most of these problems before they start. It is far less expensive to build drainage in than to add it later.
Common questions
How far should downspouts discharge from the house?
A common guideline is to discharge water several feet away from the foundation, onto ground that slopes away from the house or into a drain system. Your site conditions may call for more.
Is a French drain the same as a gutter extension?
No. A French drain is a trench with gravel and perforated pipe that collects groundwater and surface water and carries it away. It is typically used where water collects along a wall or a slope.
Can I water less near the foundation to protect it?
Aim for consistent moisture rather than dry soil. Keep sprinklers from spraying the walls and keep watering steady through the year instead of letting the soil swing from soaked to bone dry.
This guide is general information for homeowners. Every house is different, so an on site evaluation is the only way to know what your home needs.