Expansive clay around Palmdale
Vernalis 土，黏土 30%，lep=4.4（中度脹縮）; 年雨量僅 282 mm，久旱會讓黏土大幅收縮.
Vernalis 土，黏土 30%，lep=4.4（中度脹縮）
年雨量僅 282 mm，久旱會讓黏土大幅收縮
Soil sampled near Palmdale runs 30 percent clay with a linear extensibility of 4.4, which is the standard measure of how much that ground changes volume with moisture.
Why this matters for a footing
A footing is designed for a soil that stays roughly the same size. When the ground beneath one part of the house changes volume and the ground beneath another part does not, the house is asked to bridge the difference, and concrete is not good at that.
Palmdale records about 7 days a year where the temperature crosses freezing between night and day, and each of those cycles works existing cracks a little wider.
What you can do without spending much
- Get roof water away from the wall - extensions on downspouts are the cheapest intervention there is
- Keep the soil moisture around the perimeter even rather than swinging wet to bone dry
- Watch tree roots close to the footing, which draw moisture out of one side only
- Mark and date crack ends, then photograph them each season
The median home in Palmdale was built in 1990, which sets what the footing is likely to be and how deep it sits.
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